diff --git a/app/(auth)/login/page.tsx b/app/(auth)/login/page.tsx
index 7da3b810..586614f7 100644
--- a/app/(auth)/login/page.tsx
+++ b/app/(auth)/login/page.tsx
@@ -8,6 +8,7 @@ import { Label } from '@/components/ui/label'
 import { Card, CardContent, CardDescription, CardHeader, CardTitle } from '@/components/ui/card'
 import { useToast } from '@/components/ui/use-toast'
 import { Loader2, Mail, Sparkles } from 'lucide-react'
+import { getErrorMessage } from '@/lib/errors/get-error-message'
 
 export default function LoginPage() {
   const [email, setEmail] = useState('')
@@ -30,8 +31,8 @@ export default function LoginPage() {
 
       if (error) {
         toast({
-          title: 'Fel',
-          description: error.message,
+          title: 'Inloggning misslyckades',
+          description: getErrorMessage(error, { context: 'auth' }),
           variant: 'destructive',
         })
         return
@@ -42,10 +43,10 @@ export default function LoginPage() {
         title: 'E-post skickad!',
         description: 'Kolla din inkorg för att logga in.',
       })
-    } catch {
+    } catch (error) {
       toast({
-        title: 'Fel',
-        description: 'Något gick fel. Försök igen.',
+        title: 'Inloggning misslyckades',
+        description: getErrorMessage(error, { context: 'auth' }),
         variant: 'destructive',
       })
     } finally {
diff --git a/app/(dashboard)/customers/[id]/page.tsx b/app/(dashboard)/customers/[id]/page.tsx
index 0d37c4fc..74afecfc 100644
--- a/app/(dashboard)/customers/[id]/page.tsx
+++ b/app/(dashboard)/customers/[id]/page.tsx
@@ -10,6 +10,7 @@ import { Badge } from '@/components/ui/badge'
 import { Dialog, DialogContent, DialogHeader, DialogTitle } from '@/components/ui/dialog'
 import { useToast } from '@/components/ui/use-toast'
 import CustomerForm from '@/components/customers/CustomerForm'
+import { DestructiveConfirmDialog, useDestructiveConfirm } from '@/components/ui/destructive-confirm-dialog'
 import {
   ArrowLeft,
   Building,
@@ -66,6 +67,7 @@ export default function CustomerDetailPage({
   const [isLoading, setIsLoading] = useState(true)
   const [isEditOpen, setIsEditOpen] = useState(false)
   const [isUpdating, setIsUpdating] = useState(false)
+  const { dialogProps: confirmDialogProps, confirm: confirmAction } = useDestructiveConfirm()
 
   useEffect(() => {
     fetchCustomer()
@@ -124,7 +126,13 @@ export default function CustomerDetailPage({
 
   async function handleDelete() {
     if (!customer) return
-    if (!confirm(`Ta bort "${customer.name}"? Detta kan inte angras.`)) return
+    const ok = await confirmAction({
+      title: `Ta bort ${customer.name}`,
+      description: 'Kunden och tillhörande data tas bort permanent. Denna åtgärd kan inte ångras.',
+      confirmLabel: 'Ta bort',
+      variant: 'destructive',
+    })
+    if (!ok) return
 
     try {
       const response = await fetch(`/api/customers/${id}`, {
@@ -352,6 +360,8 @@ export default function CustomerDetailPage({
         </CardContent>
       </Card>
 
+      <DestructiveConfirmDialog {...confirmDialogProps} />
+
       {/* Edit dialog */}
       <Dialog open={isEditOpen} onOpenChange={setIsEditOpen}>
         <DialogContent className="max-w-2xl max-h-[90vh] overflow-y-auto">
diff --git a/app/(dashboard)/invoices/new/page.tsx b/app/(dashboard)/invoices/new/page.tsx
index f1d45320..ee07c535 100644
--- a/app/(dashboard)/invoices/new/page.tsx
+++ b/app/(dashboard)/invoices/new/page.tsx
@@ -21,6 +21,8 @@ import { Dialog, DialogContent, DialogHeader, DialogTitle, DialogDescription, Di
 import { Loader2, Plus, Trash2, ArrowLeft, Send, Eye } from 'lucide-react'
 import { ConfirmationDialog } from '@/components/ui/confirmation-dialog'
 import { InvoiceReviewContent } from '@/components/invoices/InvoiceReviewContent'
+import { getErrorMessage } from '@/lib/errors/get-error-message'
+import { useUnsavedChanges } from '@/lib/hooks/use-unsaved-changes'
 import type { Customer, Currency, CreateInvoiceInput, InvoiceDocumentType } from '@/types'
 
 const itemSchema = z.object({
@@ -73,7 +75,7 @@ export default function NewInvoicePage() {
     handleSubmit,
     watch,
     setValue,
-    formState: { errors },
+    formState: { errors, isDirty },
   } = useForm<FormData>({
     resolver: zodResolver(schema),
     defaultValues: {
@@ -86,6 +88,8 @@ export default function NewInvoicePage() {
     },
   })
 
+  useUnsavedChanges(isDirty)
+
   // Set date defaults on client only to avoid hydration mismatch
   useEffect(() => {
     setValue('invoice_date', format(new Date(), 'yyyy-MM-dd'))
@@ -209,7 +213,7 @@ export default function NewInvoicePage() {
       const result = await response.json()
 
       if (!response.ok) {
-        throw new Error(result.error || 'Kunde inte skapa faktura')
+        throw new Error(getErrorMessage(result, { context: 'invoice', statusCode: response.status }))
       }
 
       const docLabel = watchDocumentType === 'proforma' ? 'Proformafaktura' : watchDocumentType === 'delivery_note' ? 'Följesedel' : 'Faktura'
@@ -229,8 +233,8 @@ export default function NewInvoicePage() {
       }
     } catch (error) {
       toast({
-        title: 'Fel',
-        description: error instanceof Error ? error.message : 'Något gick fel',
+        title: 'Kunde inte skapa faktura',
+        description: getErrorMessage(error, { context: 'invoice' }),
         variant: 'destructive',
       })
     } finally {
@@ -249,7 +253,7 @@ export default function NewInvoicePage() {
 
       if (!response.ok) {
         const result = await response.json()
-        throw new Error(result.error || 'Kunde inte skicka faktura')
+        throw new Error(getErrorMessage(result, { context: 'invoice', statusCode: response.status }))
       }
 
       toast({
@@ -258,8 +262,8 @@ export default function NewInvoicePage() {
       })
     } catch (error) {
       toast({
-        title: 'Fel vid skickning',
-        description: error instanceof Error ? error.message : 'Något gick fel',
+        title: 'Kunde inte skicka faktura',
+        description: getErrorMessage(error, { context: 'invoice' }),
         variant: 'destructive',
       })
     } finally {
@@ -292,7 +296,7 @@ export default function NewInvoicePage() {
 
       if (!response.ok) {
         const result = await response.json()
-        throw new Error(result.error || 'Kunde inte generera förhandsgranskning')
+        throw new Error(getErrorMessage(result, { context: 'invoice', statusCode: response.status }))
       }
 
       const blob = await response.blob()
@@ -300,8 +304,8 @@ export default function NewInvoicePage() {
       window.open(url, '_blank')
     } catch (error) {
       toast({
-        title: 'Fel',
-        description: error instanceof Error ? error.message : 'Kunde inte generera PDF',
+        title: 'Kunde inte generera PDF',
+        description: getErrorMessage(error, { context: 'invoice' }),
         variant: 'destructive',
       })
     } finally {
diff --git a/app/(dashboard)/page.tsx b/app/(dashboard)/page.tsx
index bac0fa1a..51fa3067 100644
--- a/app/(dashboard)/page.tsx
+++ b/app/(dashboard)/page.tsx
@@ -170,6 +170,37 @@ export default async function DashboardPage() {
     .lt('amount', 0)
     .is('receipt_id', null)
 
+  // Count journal entries missing underlag (documents)
+  // Source types that require supporting documents
+  const needsDocSourceTypes = [
+    'manual',
+    'bank_transaction',
+    'supplier_invoice_registered',
+    'supplier_invoice_paid',
+    'supplier_invoice_cash_payment',
+    'import',
+  ]
+
+  const { count: postedEntriesCount } = await supabase
+    .from('journal_entries')
+    .select('*', { count: 'exact', head: true })
+    .eq('user_id', user.id)
+    .eq('status', 'posted')
+    .in('source_type', needsDocSourceTypes)
+
+  const { data: entriesWithDocs } = await supabase
+    .from('document_attachments')
+    .select('journal_entry_id')
+    .eq('user_id', user.id)
+    .eq('is_current_version', true)
+    .not('journal_entry_id', 'is', null)
+
+  const uniqueEntriesWithDocs = new Set(
+    (entriesWithDocs || []).map((d) => d.journal_entry_id)
+  ).size
+
+  const missingUnderlagCount = Math.max(0, (postedEntriesCount || 0) - uniqueEntriesWithDocs)
+
   // Calculate receipt streak
   const { data: recentReceiptActivity } = await supabase
     .from('receipts')
@@ -219,6 +250,7 @@ export default async function DashboardPage() {
         bankBalance,
         deadlines: (deadlines || []) as Deadline[],
         receiptQueue,
+        missingUnderlagCount,
       }}
       onboardingProgress={onboardingProgress}
     />
diff --git a/app/(dashboard)/supplier-invoices/[id]/page.tsx b/app/(dashboard)/supplier-invoices/[id]/page.tsx
index d5575cb0..49f16556 100644
--- a/app/(dashboard)/supplier-invoices/[id]/page.tsx
+++ b/app/(dashboard)/supplier-invoices/[id]/page.tsx
@@ -12,6 +12,7 @@ import { useToast } from '@/components/ui/use-toast'
 import { ArrowLeft, CheckCircle, CreditCard, FileText, Trash2 } from 'lucide-react'
 import Link from 'next/link'
 import { AccountNumber } from '@/components/ui/account-number'
+import { DestructiveConfirmDialog, useDestructiveConfirm } from '@/components/ui/destructive-confirm-dialog'
 import type { SupplierInvoice, SupplierInvoiceItem, SupplierInvoicePayment } from '@/types'
 
 function formatAmount(amount: number): string {
@@ -47,6 +48,7 @@ export default function SupplierInvoiceDetailPage() {
   const [isPayDialogOpen, setIsPayDialogOpen] = useState(false)
   const [payAmount, setPayAmount] = useState('')
   const [isProcessing, setIsProcessing] = useState(false)
+  const { dialogProps: confirmDialogProps, confirm: confirmAction } = useDestructiveConfirm()
 
   useEffect(() => {
     fetchInvoice()
@@ -100,7 +102,13 @@ export default function SupplierInvoiceDetailPage() {
   }
 
   async function handleCredit() {
-    if (!confirm('Vill du registrera en kreditfaktura för denna faktura?')) return
+    const ok = await confirmAction({
+      title: 'Registrera kreditfaktura',
+      description: 'En kreditfaktura skapas som reverserar den ursprungliga fakturan. Denna åtgärd kan inte ångras.',
+      confirmLabel: 'Registrera kreditfaktura',
+      variant: 'warning',
+    })
+    if (!ok) return
     setIsProcessing(true)
     const res = await fetch(`/api/supplier-invoices/${params.id}/credit`, { method: 'POST' })
     const result = await res.json()
@@ -114,7 +122,13 @@ export default function SupplierInvoiceDetailPage() {
   }
 
   async function handleDelete() {
-    if (!confirm('Vill du ta bort denna faktura?')) return
+    const ok = await confirmAction({
+      title: 'Ta bort faktura',
+      description: 'Fakturan och tillhörande data tas bort permanent. Denna åtgärd kan inte ångras.',
+      confirmLabel: 'Ta bort',
+      variant: 'destructive',
+    })
+    if (!ok) return
     const res = await fetch(`/api/supplier-invoices/${params.id}`, { method: 'DELETE' })
     const result = await res.json()
     if (!res.ok) {
@@ -410,6 +424,8 @@ export default function SupplierInvoiceDetailPage() {
         </Card>
       )}
 
+      <DestructiveConfirmDialog {...confirmDialogProps} />
+
       {/* Pay Dialog */}
       <Dialog open={isPayDialogOpen} onOpenChange={setIsPayDialogOpen}>
         <DialogContent>
diff --git a/app/(dashboard)/supplier-invoices/new/page.tsx b/app/(dashboard)/supplier-invoices/new/page.tsx
index aa86afa5..12316736 100644
--- a/app/(dashboard)/supplier-invoices/new/page.tsx
+++ b/app/(dashboard)/supplier-invoices/new/page.tsx
@@ -16,6 +16,8 @@ import { ConfirmationDialog } from '@/components/ui/confirmation-dialog'
 import { SupplierInvoiceReviewContent } from '@/components/suppliers/SupplierInvoiceReviewContent'
 import AccountCombobox from '@/components/bookkeeping/AccountCombobox'
 import { getAccountDescription } from '@/lib/bookkeeping/account-descriptions'
+import { getErrorMessage } from '@/lib/errors/get-error-message'
+import { useUnsavedChanges } from '@/lib/hooks/use-unsaved-changes'
 import type { Supplier, BASAccount, VatTreatment } from '@/types'
 
 interface LineItem {
@@ -67,7 +69,7 @@ export default function NewSupplierInvoicePage() {
   const [showReview, setShowReview] = useState(false)
   const [pendingData, setPendingData] = useState<FormData | null>(null)
 
-  const { register, control, handleSubmit, watch, setValue } = useForm<FormData>({
+  const { register, control, handleSubmit, watch, setValue, formState: { isDirty } } = useForm<FormData>({
     defaultValues: {
       supplier_id: '',
       supplier_invoice_number: '',
@@ -90,6 +92,8 @@ export default function NewSupplierInvoicePage() {
     },
   })
 
+  useUnsavedChanges(isDirty)
+
   const { fields, append, remove } = useFieldArray({ control, name: 'items' })
   const watchedItems = watch('items')
   const watchedSupplierId = watch('supplier_id')
@@ -208,7 +212,7 @@ export default function NewSupplierInvoicePage() {
     const result = await res.json()
 
     if (!res.ok) {
-      toast({ title: 'Fel', description: result.error || 'Kunde inte registrera faktura', variant: 'destructive' })
+      toast({ title: 'Kunde inte registrera faktura', description: getErrorMessage(result, { context: 'supplier_invoice', statusCode: res.status }), variant: 'destructive' })
     } else {
       toast({ title: 'Faktura registrerad', description: `Ankomstnummer: ${result.data.arrival_number}` })
       setShowReview(false)
diff --git a/app/(dashboard)/suppliers/[id]/page.tsx b/app/(dashboard)/suppliers/[id]/page.tsx
index 72a12d0b..d28774d9 100644
--- a/app/(dashboard)/suppliers/[id]/page.tsx
+++ b/app/(dashboard)/suppliers/[id]/page.tsx
@@ -10,6 +10,7 @@ import { useToast } from '@/components/ui/use-toast'
 import { ArrowLeft, Edit, Trash2, FileText } from 'lucide-react'
 import SupplierForm from '@/components/suppliers/SupplierForm'
 import Link from 'next/link'
+import { DestructiveConfirmDialog, useDestructiveConfirm } from '@/components/ui/destructive-confirm-dialog'
 import type { Supplier, SupplierType, CreateSupplierInput, SupplierInvoice } from '@/types'
 
 const supplierTypeLabels: Record<SupplierType, string> = {
@@ -31,6 +32,7 @@ export default function SupplierDetailPage() {
   const [isLoading, setIsLoading] = useState(true)
   const [isEditOpen, setIsEditOpen] = useState(false)
   const [isSaving, setIsSaving] = useState(false)
+  const { dialogProps: confirmDialogProps, confirm: confirmAction } = useDestructiveConfirm()
 
   useEffect(() => {
     fetchSupplier()
@@ -76,7 +78,13 @@ export default function SupplierDetailPage() {
   }
 
   async function handleDelete() {
-    if (!confirm('Är du säker på att du vill ta bort denna leverantör?')) return
+    const ok = await confirmAction({
+      title: 'Ta bort leverantör',
+      description: `"${supplier?.name}" och tillhörande data tas bort permanent. Denna åtgärd kan inte ångras.`,
+      confirmLabel: 'Ta bort',
+      variant: 'destructive',
+    })
+    if (!ok) return
 
     const res = await fetch(`/api/suppliers/${params.id}`, { method: 'DELETE' })
     const result = await res.json()
@@ -267,6 +275,8 @@ export default function SupplierDetailPage() {
         </CardContent>
       </Card>
 
+      <DestructiveConfirmDialog {...confirmDialogProps} />
+
       {/* Edit Dialog */}
       <Dialog open={isEditOpen} onOpenChange={setIsEditOpen}>
         <DialogContent className="max-w-2xl max-h-[90vh] overflow-y-auto">
diff --git a/app/(onboarding)/onboarding/page.tsx b/app/(onboarding)/onboarding/page.tsx
index 39d7dfa5..a1a64115 100644
--- a/app/(onboarding)/onboarding/page.tsx
+++ b/app/(onboarding)/onboarding/page.tsx
@@ -6,6 +6,7 @@ import { createClient } from '@/lib/supabase/client'
 import { Progress } from '@/components/ui/progress'
 import { useToast } from '@/components/ui/use-toast'
 import { Loader2 } from 'lucide-react'
+import { validatePeriodDuration } from '@/lib/bookkeeping/validate-period-duration'
 import type { CompanySettings, EntityType, MomsPeriod } from '@/types'
 
 import Step1EntityType from '@/components/onboarding/Step1EntityType'
@@ -26,6 +27,14 @@ const STEP_TITLES = [
   'Tillägg',
 ]
 
+function translatePeriodError(msg: string): string {
+  if (msg.includes('end must be after')) return 'Slutdatumet måste vara efter startdatumet.'
+  if (msg.includes('start must be the 1st')) return 'Startdatumet måste vara den 1:a i en månad.'
+  if (msg.includes('end must be the last day')) return 'Slutdatumet måste vara sista dagen i en månad.'
+  if (msg.includes('exceeds maximum 18 months')) return 'Räkenskapsåret får inte överstiga 18 månader (BFL 3 kap.).'
+  return 'Ogiltigt räkenskapsår. Kontrollera datumen och försök igen.'
+}
+
 export default function OnboardingPage() {
   return (
     <Suspense fallback={<div className="flex items-center justify-center h-64"><Loader2 className="h-8 w-8 animate-spin text-primary" /></div>}>
@@ -210,26 +219,33 @@ function OnboardingPageContent() {
                 : `Räkenskapsår ${currentYear}/${currentYear + 1}`
             }
 
-            // Validate period duration (max 18 months)
-            const startDate = new Date(startStr)
-            const endDate = new Date(endStr)
-            const months = (endDate.getFullYear() - startDate.getFullYear()) * 12 +
-              (endDate.getMonth() - startDate.getMonth()) + 1
-            if (months > 18) {
-              console.error(`Period duration ${months} months exceeds 18-month maximum`)
-            } else {
-              await supabase.from('fiscal_periods').upsert({
-                user_id: user.id,
-                name: periodName,
-                period_start: startStr,
-                period_end: endStr,
-              }, {
-                onConflict: 'user_id,period_start,period_end',
+            // Validate period duration
+            const validationError = validatePeriodDuration(startStr, endStr)
+            if (validationError) {
+              toast({
+                title: 'Ogiltigt räkenskapsår',
+                description: translatePeriodError(validationError),
+                variant: 'destructive',
               })
+              setCurrentStep(3)
+              return
             }
+
+            await supabase.from('fiscal_periods').upsert({
+              user_id: user.id,
+              name: periodName,
+              period_start: startStr,
+              period_end: endStr,
+            }, {
+              onConflict: 'user_id,period_start,period_end',
+            })
           }
         } catch (err) {
-          console.error('Failed to create fiscal period:', err)
+          toast({
+            title: 'Kunde inte skapa räkenskapsår',
+            description: 'Ett fel uppstod när räkenskapsåret skulle skapas. Försök igen.',
+            variant: 'destructive',
+          })
         }
       }
 
diff --git a/app/api/extensions/push-notifications/cron/route.ts b/app/api/extensions/push-notifications/cron/route.ts
index 12cc79ce..c4b8087c 100644
--- a/app/api/extensions/push-notifications/cron/route.ts
+++ b/app/api/extensions/push-notifications/cron/route.ts
@@ -4,6 +4,7 @@ import { loadExtensions } from '@/lib/extensions/loader'
 import {
   sendTaxDeadlineNotifications,
   sendInvoiceNotifications,
+  sendMissingUnderlagNotifications,
 } from '@/extensions/general/push-notifications/notification-scheduler'
 
 /**
@@ -40,13 +41,14 @@ export async function GET(request: Request) {
 
   try {
     // Send all notification types in parallel
-    const [taxResult, invoiceResult] = await Promise.all([
+    const [taxResult, invoiceResult, underlagResult] = await Promise.all([
       sendTaxDeadlineNotifications(supabase),
       sendInvoiceNotifications(supabase),
+      sendMissingUnderlagNotifications(supabase),
     ])
 
-    const totalSent = taxResult.sent + invoiceResult.sent
-    const totalSkipped = taxResult.skipped + invoiceResult.skipped
+    const totalSent = taxResult.sent + invoiceResult.sent + underlagResult.sent
+    const totalSkipped = taxResult.skipped + invoiceResult.skipped + underlagResult.skipped
 
     console.log(
       `Push notification cron completed: ${totalSent} sent, ${totalSkipped} skipped`
@@ -57,6 +59,9 @@ export async function GET(request: Request) {
     console.log(
       `  Invoice: ${invoiceResult.sent} sent, ${invoiceResult.skipped} skipped`
     )
+    console.log(
+      `  Missing underlag: ${underlagResult.sent} sent, ${underlagResult.skipped} skipped`
+    )
 
     return NextResponse.json({
       success: true,
@@ -65,6 +70,7 @@ export async function GET(request: Request) {
       details: {
         taxDeadlines: taxResult,
         invoices: invoiceResult,
+        missingUnderlag: underlagResult,
       },
     })
   } catch (error) {
diff --git a/app/api/invoices/[id]/send/route.ts b/app/api/invoices/[id]/send/route.ts
index 1ae8249d..bf647d1b 100644
--- a/app/api/invoices/[id]/send/route.ts
+++ b/app/api/invoices/[id]/send/route.ts
@@ -11,6 +11,7 @@ import {
   generateInvoiceEmailSubject
 } from '@/lib/email/invoice-templates'
 import { createInvoiceJournalEntry } from '@/lib/bookkeeping/invoice-entries'
+import { uploadDocument } from '@/lib/core/documents/document-service'
 import type { Invoice, InvoiceItem, Customer, CompanySettings } from '@/types'
 
 ensureInitialized()
@@ -166,6 +167,7 @@ export async function POST(
 
     // Only create journal entries for real invoices (not proformas or delivery notes)
     const isRealInvoice = !invoice.document_type || invoice.document_type === 'invoice'
+    let createdJournalEntryId: string | undefined
     if (isRealInvoice && ((company as Record<string, unknown>).accounting_method === 'accrual' || !(company as Record<string, unknown>).accounting_method)) {
       try {
         const journalEntry = await createInvoiceJournalEntry(
@@ -174,6 +176,7 @@ export async function POST(
           (company as CompanySettings).entity_type
         )
         if (journalEntry) {
+          createdJournalEntryId = journalEntry.id
           await supabase
             .from('invoices')
             .update({ journal_entry_id: journalEntry.id })
@@ -185,6 +188,24 @@ export async function POST(
       }
     }
 
+    // Auto-store invoice PDF as underlag and link to journal entry
+    if (isRealInvoice) {
+      try {
+        const pdfArrayBuffer = new Uint8Array(pdfBuffer).buffer as ArrayBuffer
+        await uploadDocument(user.id, {
+          name: filename,
+          buffer: pdfArrayBuffer,
+          type: 'application/pdf',
+        }, {
+          upload_source: 'system',
+          journal_entry_id: createdJournalEntryId,
+        })
+      } catch (err) {
+        console.error('Failed to store invoice PDF as underlag:', err)
+        // Non-blocking — don't fail the send
+      }
+    }
+
     await eventBus.emit({
       type: 'invoice.sent',
       payload: { invoice: invoice as Invoice, userId: user.id },
diff --git a/app/page.tsx b/app/page.tsx
index 9143e22a..80b5e80d 100644
--- a/app/page.tsx
+++ b/app/page.tsx
@@ -136,6 +136,36 @@ export default async function RootPage() {
     .lt('amount', 0)
     .is('receipt_id', null)
 
+  // Count journal entries missing underlag (documents)
+  const needsDocSourceTypes = [
+    'manual',
+    'bank_transaction',
+    'supplier_invoice_registered',
+    'supplier_invoice_paid',
+    'supplier_invoice_cash_payment',
+    'import',
+  ]
+
+  const { count: postedEntriesCount } = await supabase
+    .from('journal_entries')
+    .select('*', { count: 'exact', head: true })
+    .eq('user_id', user.id)
+    .eq('status', 'posted')
+    .in('source_type', needsDocSourceTypes)
+
+  const { data: entriesWithDocs } = await supabase
+    .from('document_attachments')
+    .select('journal_entry_id')
+    .eq('user_id', user.id)
+    .eq('is_current_version', true)
+    .not('journal_entry_id', 'is', null)
+
+  const uniqueEntriesWithDocs = new Set(
+    (entriesWithDocs || []).map((d) => d.journal_entry_id)
+  ).size
+
+  const missingUnderlagCount = Math.max(0, (postedEntriesCount || 0) - uniqueEntriesWithDocs)
+
   // Calculate receipt streak
   const { data: recentReceiptActivity } = await supabase
     .from('receipts')
@@ -188,6 +218,7 @@ export default async function RootPage() {
               bankBalance,
               deadlines: (deadlines || []) as Deadline[],
               receiptQueue,
+              missingUnderlagCount,
             }}
           />
         </div>
diff --git a/components/bookkeeping/JournalEntryForm.tsx b/components/bookkeeping/JournalEntryForm.tsx
index 1384ad0c..ede79797 100644
--- a/components/bookkeeping/JournalEntryForm.tsx
+++ b/components/bookkeeping/JournalEntryForm.tsx
@@ -6,11 +6,13 @@ import { Button } from '@/components/ui/button'
 import { Input } from '@/components/ui/input'
 import { Label } from '@/components/ui/label'
 import { useToast } from '@/components/ui/use-toast'
-import { Plus, Trash2 } from 'lucide-react'
+import { Plus, Trash2, AlertTriangle } from 'lucide-react'
 import { ConfirmationDialog } from '@/components/ui/confirmation-dialog'
 import { JournalEntryReviewContent } from '@/components/bookkeeping/JournalEntryReviewContent'
 import DocumentUploadZone from '@/components/bookkeeping/DocumentUploadZone'
 import AccountCombobox from '@/components/bookkeeping/AccountCombobox'
+import { getErrorMessage } from '@/lib/errors/get-error-message'
+import { useUnsavedChanges } from '@/lib/hooks/use-unsaved-changes'
 import type { UploadedFile } from '@/components/bookkeeping/DocumentUploadZone'
 import type { CreateJournalEntryLineInput, FiscalPeriod, BASAccount, JournalEntrySourceType } from '@/types'
 
@@ -56,11 +58,17 @@ export default function JournalEntryForm({
   )
   const [isSubmitting, setIsSubmitting] = useState(false)
   const [showReview, setShowReview] = useState(false)
+  const [showNoDocWarning, setShowNoDocWarning] = useState(false)
   const [uploadedFiles, setUploadedFiles] = useState<UploadedFile[]>([])
   const [accounts, setAccounts] = useState<BASAccount[]>([])
 
   const isUploading = uploadedFiles.some((f) => f.status === 'uploading')
 
+  const hasContent = description !== '' ||
+    lines.some(l => l.account_number !== '' || l.debit_amount !== '' || l.credit_amount !== '') ||
+    uploadedFiles.length > 0
+  useUnsavedChanges(hasContent)
+
   useEffect(() => {
     fetchPeriods()
     fetchAccounts()
@@ -118,6 +126,11 @@ export default function JournalEntryForm({
 
   const handleReview = () => {
     if (!selectedPeriod || !description || !isBalanced) return
+    const hasDocuments = uploadedFiles.some((f) => f.status === 'uploaded')
+    if (!embedded && !hasDocuments) {
+      setShowNoDocWarning(true)
+      return
+    }
     setShowReview(true)
   }
 
@@ -152,8 +165,8 @@ export default function JournalEntryForm({
 
     if (result.error) {
       toast({
-        title: 'Fel',
-        description: result.error,
+        title: 'Kunde inte skapa verifikation',
+        description: getErrorMessage(result, { context: 'journal_entry', statusCode: res.status }),
         variant: 'destructive',
       })
     } else {
@@ -161,6 +174,7 @@ export default function JournalEntryForm({
       const journalEntryId = result.data?.id ?? result.journal_entry_id
       if (journalEntryId && uploadedFiles.length > 0) {
         const filesToLink = uploadedFiles.filter((f) => f.status === 'uploaded' && f.id)
+        let linkFailCount = 0
         for (const file of filesToLink) {
           try {
             await fetch(`/api/documents/${file.id}/link`, {
@@ -170,8 +184,16 @@ export default function JournalEntryForm({
             })
           } catch (linkErr) {
             console.error('[JournalEntryForm] Failed to link document:', linkErr)
+            linkFailCount++
           }
         }
+        if (linkFailCount > 0) {
+          toast({
+            title: 'Underlag kunde inte bifogas',
+            description: `${linkFailCount} fil(er) kunde inte lankas till verifikationen. Forsok igen via bokforingssidan.`,
+            variant: 'destructive',
+          })
+        }
       }
 
       toast({
@@ -379,6 +401,31 @@ export default function JournalEntryForm({
           attachmentCount={uploadedFiles.filter((f) => f.status === 'uploaded').length}
         />
       </ConfirmationDialog>
+
+      {/* Warning dialog when no documents attached */}
+      <ConfirmationDialog
+        open={showNoDocWarning}
+        onOpenChange={setShowNoDocWarning}
+        onConfirm={() => {
+          setShowNoDocWarning(false)
+          setShowReview(true)
+        }}
+        isSubmitting={false}
+        title="Underlag saknas"
+        warningText="Ingen verifikation har bifogats. Enligt bokforingslagen (BFL) kravs underlag for varje bokforingspost."
+        confirmLabel="Fortsatt anda"
+      >
+        <div className="flex items-start gap-3 rounded-lg border border-amber-200 dark:border-amber-800 bg-amber-50 dark:bg-amber-950/30 p-4">
+          <AlertTriangle className="h-5 w-5 text-amber-600 dark:text-amber-400 mt-0.5 shrink-0" />
+          <div className="text-sm text-amber-800 dark:text-amber-300">
+            <p className="font-medium mb-1">Inget underlag bifogat</p>
+            <p>
+              Enligt bokforingslagen (BFL 5 kap. 6-7 §§) ska varje bokforingspost ha en verifikation som
+              underlag. Du kan bifoga underlag nu eller fortsatta utan.
+            </p>
+          </div>
+        </div>
+      </ConfirmationDialog>
     </div>
   )
 
diff --git a/components/dashboard/DashboardContent.tsx b/components/dashboard/DashboardContent.tsx
index 97a1362d..5d591832 100644
--- a/components/dashboard/DashboardContent.tsx
+++ b/components/dashboard/DashboardContent.tsx
@@ -28,6 +28,7 @@ import {
   CheckCircle2,
   ClipboardList,
   MessageCircle,
+  FileWarning,
 } from 'lucide-react'
 import type { CompanySettings, EntityType, Deadline, ReceiptQueueSummary, OnboardingProgress } from '@/types'
 
@@ -47,6 +48,7 @@ interface DashboardContentProps {
     bankBalance: number | null
     deadlines: Deadline[]
     receiptQueue: ReceiptQueueSummary | null
+    missingUnderlagCount: number
   }
   onboardingProgress?: OnboardingProgress
 }
@@ -176,6 +178,29 @@ export default function DashboardContent({ firstName, settings, summary, onboard
     )
   }
 
+  if (summary.missingUnderlagCount > 0) {
+    alertItems.push(
+      <Link key="missing-underlag" href="/bookkeeping?missingUnderlag=true" className="group">
+        <Card className="h-full border-l-2 border-l-warning hover:bg-muted/20 transition-colors">
+          <CardContent className="p-4">
+            <div className="flex items-center justify-between">
+              <div className="flex items-center gap-3">
+                <FileWarning className="h-4 w-4 text-warning-foreground flex-shrink-0" />
+                <div>
+                  <p className="font-medium text-sm">Saknade underlag</p>
+                  <p className="text-xs text-muted-foreground mt-0.5">
+                    {summary.missingUnderlagCount} verifikationer utan underlag
+                  </p>
+                </div>
+              </div>
+              <ArrowRight className="h-3.5 w-3.5 text-muted-foreground/50 group-hover:text-muted-foreground group-hover:translate-x-0.5 transition-all" />
+            </div>
+          </CardContent>
+        </Card>
+      </Link>
+    )
+  }
+
   const MAX_VISIBLE_ALERTS = 3
   const visibleAlerts = showAllAlerts ? alertItems : alertItems.slice(0, MAX_VISIBLE_ALERTS)
   const hasMoreAlerts = alertItems.length > MAX_VISIBLE_ALERTS
@@ -228,6 +253,9 @@ export default function DashboardContent({ firstName, settings, summary, onboard
         if (summary.receiptQueue && summary.receiptQueue.pending_review_count > 0) {
           todoItems.push({ label: 'kvitton att granska', href: '/receipts', count: summary.receiptQueue.pending_review_count, variant: 'default' })
         }
+        if (summary.missingUnderlagCount > 0) {
+          todoItems.push({ label: 'saknade underlag', href: '/bookkeeping?missingUnderlag=true', count: summary.missingUnderlagCount, variant: 'warning' })
+        }
 
         if (todoItems.length === 0) return null
 
diff --git a/components/onboarding/Step3TaxRegistration.tsx b/components/onboarding/Step3TaxRegistration.tsx
index e1882faf..733733a0 100644
--- a/components/onboarding/Step3TaxRegistration.tsx
+++ b/components/onboarding/Step3TaxRegistration.tsx
@@ -11,8 +11,9 @@ import { Label } from '@/components/ui/label'
 import { Checkbox } from '@/components/ui/checkbox'
 import { Select, SelectContent, SelectItem, SelectTrigger, SelectValue } from '@/components/ui/select'
 import { InfoTooltip } from '@/components/ui/info-tooltip'
-import { Loader2, ArrowRight, ArrowLeft, Check } from 'lucide-react'
+import { Loader2, ArrowRight, ArrowLeft, Check, CalendarDays, Info } from 'lucide-react'
 import { cn } from '@/lib/utils'
+import { monthsBetween } from '@/lib/bookkeeping/validate-period-duration'
 import type { MomsPeriod, EntityType } from '@/types'
 
 const schema = z.object({
@@ -58,6 +59,14 @@ const monthNames = [
   'Juli', 'Augusti', 'September', 'Oktober', 'November', 'December',
 ]
 
+function formatSwedishDate(dateStr: string): string {
+  const d = new Date(dateStr)
+  const day = d.getDate()
+  const month = monthNames[d.getMonth()].toLowerCase()
+  const year = d.getFullYear()
+  return `${day} ${month} ${year}`
+}
+
 /**
  * Get the last day of a given month (1-indexed).
  */
@@ -163,6 +172,7 @@ export default function Step3TaxRegistration({
   const firstYearStart = watch('first_year_start')
   const firstYearEnd = watch('first_year_end')
   const fiscalYearEndMonth = watch('fiscal_year_end_month')
+  const accountingMethod = watch('accounting_method')
 
   // State for AB first-year end month selector
   const [abEndMonth, setAbEndMonth] = useState<number>(
@@ -424,6 +434,21 @@ export default function Step3TaxRegistration({
                       Ingen giltig slutperiod hittades. Kontrollera startdatumet.
                     </p>
                   )}
+
+                  {firstYearStart && firstYearEnd && (
+                    <div className="rounded-lg border border-primary/20 bg-primary/5 p-4 space-y-1">
+                      <div className="flex items-center gap-2 text-sm font-medium">
+                        <CalendarDays className="h-4 w-4 text-primary" />
+                        Ditt första räkenskapsår
+                      </div>
+                      <p className="text-sm text-muted-foreground">
+                        {formatSwedishDate(firstYearStart)} &ndash; {formatSwedishDate(firstYearEnd)}
+                      </p>
+                      <p className="text-xs text-muted-foreground">
+                        {monthsBetween(firstYearStart, firstYearEnd)} månader
+                      </p>
+                    </div>
+                  )}
                 </div>
               )}
 
@@ -464,6 +489,21 @@ export default function Step3TaxRegistration({
                       <p className="text-sm text-muted-foreground">
                         De flesta har kalenderår (december). Brutet räkenskapsår slutar annan månad.
                       </p>
+
+                      {fiscalYearEndMonth && (
+                        <div className="mt-3 rounded-lg border border-primary/20 bg-primary/5 p-4 space-y-1">
+                          <div className="flex items-center gap-2 text-sm font-medium">
+                            <CalendarDays className="h-4 w-4 text-primary" />
+                            Ditt räkenskapsår
+                          </div>
+                          <p className="text-sm text-muted-foreground">
+                            {fiscalYearEndMonth === 12
+                              ? `1 januari \u2013 31 december (kalenderår)`
+                              : `1 ${monthNames[fiscalYearEndMonth].toLowerCase()} \u2013 ${lastDayOfMonth(2025, fiscalYearEndMonth)} ${monthNames[fiscalYearEndMonth - 1].toLowerCase()}`}
+                          </p>
+                          <p className="text-xs text-muted-foreground">12 månader</p>
+                        </div>
+                      )}
                     </div>
                   )}
                 </div>
@@ -594,11 +634,22 @@ export default function Step3TaxRegistration({
                     </Select>
                   )}
                 />
-                <p className="text-xs text-muted-foreground">
-                  {entityType === 'aktiebolag'
-                    ? 'Aktiebolag med omsättning över 3 MSEK måste använda faktureringsmetoden.'
-                    : 'Som enskild firma med omsättning under 3 MSEK kan du välja kontantmetoden.'}
-                </p>
+                <div className="rounded-lg border bg-muted/50 p-4 space-y-2">
+                  <div className="flex items-center gap-2 text-sm font-medium">
+                    <Info className="h-4 w-4 text-muted-foreground" />
+                    {accountingMethod === 'accrual' ? 'Faktureringsmetoden' : 'Kontantmetoden'}
+                  </div>
+                  <p className="text-sm text-muted-foreground">
+                    {accountingMethod === 'accrual'
+                      ? 'Intäkter och kostnader bokförs när fakturan skickas eller tas emot, oavsett när betalningen sker. Detta ger en mer rättvisande bild av verksamhetens ekonomi.'
+                      : 'Intäkter och kostnader bokförs först när betalningen faktiskt sker. Enklare att hantera men ger en mindre exakt bild av verksamhetens ekonomi vid varje given tidpunkt.'}
+                  </p>
+                  {entityType === 'aktiebolag' && (
+                    <p className="text-xs text-amber-700 bg-amber-50 rounded px-2 py-1">
+                      Aktiebolag med omsättning över 3 MSEK per år måste använda faktureringsmetoden.
+                    </p>
+                  )}
+                </div>
               </div>
             </div>
 
diff --git a/components/settings/CalendarFeedSettings.tsx b/components/settings/CalendarFeedSettings.tsx
index 200f80b4..eae0696e 100644
--- a/components/settings/CalendarFeedSettings.tsx
+++ b/components/settings/CalendarFeedSettings.tsx
@@ -9,6 +9,7 @@ import { Input } from '@/components/ui/input'
 import { useToast } from '@/components/ui/use-toast'
 import { Badge } from '@/components/ui/badge'
 import { Calendar, Copy, RefreshCw, Loader2, ExternalLink, Check } from 'lucide-react'
+import { DestructiveConfirmDialog, useDestructiveConfirm } from '@/components/ui/destructive-confirm-dialog'
 import type { CalendarFeed } from '@/types'
 
 interface CalendarFeedWithUrls extends CalendarFeed {
@@ -24,6 +25,7 @@ export function CalendarFeedSettings() {
   const [isRegenerating, setIsRegenerating] = useState(false)
   const [feed, setFeed] = useState<CalendarFeedWithUrls | null>(null)
   const [copied, setCopied] = useState(false)
+  const { dialogProps: confirmDialogProps, confirm: confirmAction } = useDestructiveConfirm()
 
   useEffect(() => {
     fetchFeed()
@@ -99,9 +101,13 @@ export function CalendarFeedSettings() {
   }
 
   const regenerateToken = async () => {
-    if (!confirm('Är du säker? Den gamla länken kommer sluta fungera.')) {
-      return
-    }
+    const ok = await confirmAction({
+      title: 'Skapa ny kalender-länk',
+      description: 'Den gamla länken slutar fungera omedelbart. Du behöver uppdatera länken i alla kalenderappar som använder den.',
+      confirmLabel: 'Skapa ny länk',
+      variant: 'warning',
+    })
+    if (!ok) return
 
     setIsRegenerating(true)
 
@@ -334,6 +340,8 @@ export function CalendarFeedSettings() {
 
         </CardContent>
       </Card>
+
+      <DestructiveConfirmDialog {...confirmDialogProps} />
     </div>
   )
 }
diff --git a/components/transactions/TransactionBookingDialog.tsx b/components/transactions/TransactionBookingDialog.tsx
index a47c1357..92cdc724 100644
--- a/components/transactions/TransactionBookingDialog.tsx
+++ b/components/transactions/TransactionBookingDialog.tsx
@@ -1,9 +1,15 @@
 'use client'
 
+import { useState } from 'react'
 import { Dialog, DialogContent, DialogHeader, DialogTitle, DialogDescription } from '@/components/ui/dialog'
+import { Button } from '@/components/ui/button'
+import { Label } from '@/components/ui/label'
+import { useToast } from '@/components/ui/use-toast'
 import { formatCurrency, formatDate } from '@/lib/utils'
-import { ArrowUpRight, ArrowDownRight } from 'lucide-react'
+import { ArrowUpRight, ArrowDownRight, ChevronDown, ChevronUp, Paperclip } from 'lucide-react'
 import JournalEntryForm from '@/components/bookkeeping/JournalEntryForm'
+import DocumentUploadZone from '@/components/bookkeeping/DocumentUploadZone'
+import type { UploadedFile } from '@/components/bookkeeping/DocumentUploadZone'
 import type { FormLine } from '@/components/bookkeeping/JournalEntryForm'
 import type { TransactionWithInvoice } from './transaction-types'
 
@@ -38,17 +44,58 @@ export default function TransactionBookingDialog({
   transaction,
   onBooked,
 }: TransactionBookingDialogProps) {
+  const { toast } = useToast()
+  const [uploadedFiles, setUploadedFiles] = useState<UploadedFile[]>([])
+  const [showUploadZone, setShowUploadZone] = useState(false)
+
   if (!transaction) return null
 
   const isIncome = transaction.amount > 0
 
+  const handleBooked = async (transactionId: string, journalEntryId: string) => {
+    // Link any uploaded documents to the new journal entry
+    const filesToLink = uploadedFiles.filter((f) => f.status === 'uploaded' && f.id)
+    if (filesToLink.length > 0) {
+      let linkFailCount = 0
+      for (const file of filesToLink) {
+        try {
+          await fetch(`/api/documents/${file.id}/link`, {
+            method: 'POST',
+            headers: { 'Content-Type': 'application/json' },
+            body: JSON.stringify({ journal_entry_id: journalEntryId }),
+          })
+        } catch (linkErr) {
+          console.error('[TransactionBookingDialog] Failed to link document:', linkErr)
+          linkFailCount++
+        }
+      }
+      if (linkFailCount > 0) {
+        toast({
+          title: 'Underlag kunde inte bifogas',
+          description: `${linkFailCount} fil(er) kunde inte lankas till verifikationen. Forsok igen via bokforingssidan.`,
+          variant: 'destructive',
+        })
+      }
+    }
+
+    setUploadedFiles([])
+    setShowUploadZone(false)
+    onBooked(transactionId, journalEntryId)
+  }
+
   return (
-    <Dialog open={open} onOpenChange={onOpenChange}>
+    <Dialog open={open} onOpenChange={(o) => {
+      if (!o) {
+        setUploadedFiles([])
+        setShowUploadZone(false)
+      }
+      onOpenChange(o)
+    }}>
       <DialogContent className="max-w-2xl max-h-[90vh] overflow-y-auto">
         <DialogHeader>
-          <DialogTitle>Bokför transaktion</DialogTitle>
+          <DialogTitle>Bokfor transaktion</DialogTitle>
           <DialogDescription>
-            Skapa en verifikation för transaktionen
+            Skapa en verifikation for transaktionen
           </DialogDescription>
         </DialogHeader>
 
@@ -77,6 +124,39 @@ export default function TransactionBookingDialog({
           </p>
         </div>
 
+        {/* Document upload section */}
+        <div className="rounded-lg border">
+          <button
+            type="button"
+            onClick={() => setShowUploadZone(!showUploadZone)}
+            className="flex items-center justify-between w-full px-3 py-2.5 text-sm hover:bg-muted/50 transition-colors"
+          >
+            <div className="flex items-center gap-2">
+              <Paperclip className="h-4 w-4 text-muted-foreground" />
+              <span className="font-medium">Underlag (valfritt)</span>
+              {uploadedFiles.filter((f) => f.status === 'uploaded').length > 0 && (
+                <span className="text-xs text-muted-foreground">
+                  {uploadedFiles.filter((f) => f.status === 'uploaded').length} bifogade
+                </span>
+              )}
+            </div>
+            {showUploadZone ? (
+              <ChevronUp className="h-4 w-4 text-muted-foreground" />
+            ) : (
+              <ChevronDown className="h-4 w-4 text-muted-foreground" />
+            )}
+          </button>
+          {showUploadZone && (
+            <div className="px-3 pb-3">
+              <DocumentUploadZone
+                files={uploadedFiles}
+                onFilesChange={setUploadedFiles}
+                compact
+              />
+            </div>
+          )}
+        </div>
+
         <JournalEntryForm
           key={transaction.id}
           embedded
@@ -86,7 +166,7 @@ export default function TransactionBookingDialog({
           submitUrl={`/api/transactions/${transaction.id}/book`}
           sourceType="bank_transaction"
           sourceId={transaction.id}
-          onEntryCreated={(entryId) => onBooked(transaction.id, entryId)}
+          onEntryCreated={(entryId) => handleBooked(transaction.id, entryId)}
         />
       </DialogContent>
     </Dialog>
diff --git a/components/ui/destructive-confirm-dialog.tsx b/components/ui/destructive-confirm-dialog.tsx
new file mode 100644
index 00000000..136d0803
--- /dev/null
+++ b/components/ui/destructive-confirm-dialog.tsx
@@ -0,0 +1,179 @@
+'use client'
+
+import { useState, useCallback, useRef } from 'react'
+import {
+  Dialog,
+  DialogContent,
+  DialogHeader,
+  DialogTitle,
+  DialogDescription,
+  DialogFooter,
+} from '@/components/ui/dialog'
+import { Button } from '@/components/ui/button'
+import { AlertTriangle, Loader2 } from 'lucide-react'
+import { cn } from '@/lib/utils'
+
+interface DestructiveConfirmDialogProps {
+  open: boolean
+  onOpenChange: (open: boolean) => void
+  title: string
+  description: string
+  confirmLabel?: string
+  cancelLabel?: string
+  variant?: 'destructive' | 'warning'
+  onConfirm: () => void | Promise<void>
+}
+
+export function DestructiveConfirmDialog({
+  open,
+  onOpenChange,
+  title,
+  description,
+  confirmLabel = 'Bekräfta',
+  cancelLabel = 'Avbryt',
+  variant = 'destructive',
+  onConfirm,
+}: DestructiveConfirmDialogProps) {
+  const [isLoading, setIsLoading] = useState(false)
+
+  const handleConfirm = async () => {
+    setIsLoading(true)
+    try {
+      await onConfirm()
+    } finally {
+      setIsLoading(false)
+      onOpenChange(false)
+    }
+  }
+
+  return (
+    <Dialog
+      open={open}
+      onOpenChange={(v) => {
+        if (isLoading) return
+        onOpenChange(v)
+      }}
+    >
+      <DialogContent className="sm:max-w-md">
+        <DialogHeader>
+          <div className="flex items-start gap-4">
+            <div
+              className={cn(
+                'flex-shrink-0 flex items-center justify-center h-10 w-10 rounded-full',
+                variant === 'destructive'
+                  ? 'bg-red-100 text-red-600'
+                  : 'bg-amber-100 text-amber-600'
+              )}
+            >
+              <AlertTriangle className="h-5 w-5" />
+            </div>
+            <div className="space-y-1">
+              <DialogTitle>{title}</DialogTitle>
+              <DialogDescription>{description}</DialogDescription>
+            </div>
+          </div>
+        </DialogHeader>
+        <DialogFooter className="gap-2 sm:gap-0">
+          <Button
+            variant="outline"
+            onClick={() => onOpenChange(false)}
+            disabled={isLoading}
+          >
+            {cancelLabel}
+          </Button>
+          <Button
+            variant={variant === 'destructive' ? 'destructive' : 'default'}
+            onClick={handleConfirm}
+            disabled={isLoading}
+            className={
+              variant === 'warning'
+                ? 'bg-amber-600 hover:bg-amber-700 text-white'
+                : undefined
+            }
+          >
+            {isLoading ? (
+              <Loader2 className="mr-2 h-4 w-4 animate-spin" />
+            ) : null}
+            {confirmLabel}
+          </Button>
+        </DialogFooter>
+      </DialogContent>
+    </Dialog>
+  )
+}
+
+interface ConfirmOptions {
+  title: string
+  description: string
+  confirmLabel?: string
+  cancelLabel?: string
+  variant?: 'destructive' | 'warning'
+}
+
+interface UseDestructiveConfirmReturn {
+  dialogProps: DestructiveConfirmDialogProps
+  confirm: (options: ConfirmOptions) => Promise<boolean>
+}
+
+/**
+ * Hook that returns a `confirm()` function as a drop-in replacement for `window.confirm()`.
+ * Returns `Promise<boolean>` — true if user confirms, false if they cancel.
+ *
+ * Usage:
+ * ```
+ * const { dialogProps, confirm } = useDestructiveConfirm()
+ *
+ * async function handleDelete() {
+ *   const ok = await confirm({ title: '...', description: '...' })
+ *   if (!ok) return
+ *   // proceed with deletion
+ * }
+ *
+ * return <><DestructiveConfirmDialog {...dialogProps} /></>
+ * ```
+ */
+export function useDestructiveConfirm(): UseDestructiveConfirmReturn {
+  const [open, setOpen] = useState(false)
+  const [options, setOptions] = useState<ConfirmOptions>({
+    title: '',
+    description: '',
+  })
+  const resolveRef = useRef<((value: boolean) => void) | null>(null)
+
+  const confirm = useCallback((opts: ConfirmOptions): Promise<boolean> => {
+    setOptions(opts)
+    setOpen(true)
+    return new Promise<boolean>((resolve) => {
+      resolveRef.current = resolve
+    })
+  }, [])
+
+  const handleOpenChange = useCallback((v: boolean) => {
+    setOpen(v)
+    if (!v && resolveRef.current) {
+      resolveRef.current(false)
+      resolveRef.current = null
+    }
+  }, [])
+
+  const handleConfirm = useCallback(() => {
+    if (resolveRef.current) {
+      resolveRef.current(true)
+      resolveRef.current = null
+    }
+  }, [])
+
+  return {
+    dialogProps: {
+      open,
+      onOpenChange: handleOpenChange,
+      title: options.title,
+      description: options.description,
+      confirmLabel: options.confirmLabel,
+      cancelLabel: options.cancelLabel,
+      variant: options.variant,
+      onConfirm: handleConfirm,
+    },
+    confirm,
+  }
+}
diff --git a/extensions/general/push-notifications/index.ts b/extensions/general/push-notifications/index.ts
index 7fbd0d98..58d2c938 100644
--- a/extensions/general/push-notifications/index.ts
+++ b/extensions/general/push-notifications/index.ts
@@ -30,6 +30,7 @@ export interface PushNotificationSettings {
   invoiceSentEnabled: boolean
   receiptExtractedEnabled: boolean
   receiptMatchedEnabled: boolean
+  missingUnderlagEnabled: boolean
 }
 
 const DEFAULT_SETTINGS: PushNotificationSettings = {
@@ -38,6 +39,7 @@ const DEFAULT_SETTINGS: PushNotificationSettings = {
   invoiceSentEnabled: false,
   receiptExtractedEnabled: true,
   receiptMatchedEnabled: true,
+  missingUnderlagEnabled: true,
 }
 
 /** Get settings via ExtensionContext (preferred in event handlers) */
@@ -54,7 +56,7 @@ export async function getSettings(userId: string): Promise<PushNotificationSetti
   const { data } = await supabase
     .from('notification_settings')
     .select(
-      'period_locked_enabled, period_year_closed_enabled, invoice_sent_enabled, receipt_extracted_enabled, receipt_matched_enabled'
+      'period_locked_enabled, period_year_closed_enabled, invoice_sent_enabled, receipt_extracted_enabled, receipt_matched_enabled, missing_underlag_enabled'
     )
     .eq('user_id', userId)
     .single()
@@ -66,6 +68,7 @@ export async function getSettings(userId: string): Promise<PushNotificationSetti
     invoiceSentEnabled: data.invoice_sent_enabled ?? DEFAULT_SETTINGS.invoiceSentEnabled,
     receiptExtractedEnabled: data.receipt_extracted_enabled ?? DEFAULT_SETTINGS.receiptExtractedEnabled,
     receiptMatchedEnabled: data.receipt_matched_enabled ?? DEFAULT_SETTINGS.receiptMatchedEnabled,
+    missingUnderlagEnabled: data.missing_underlag_enabled ?? DEFAULT_SETTINGS.missingUnderlagEnabled,
   }
 }
 
@@ -89,6 +92,7 @@ export async function saveSettings(
         invoice_sent_enabled: merged.invoiceSentEnabled,
         receipt_extracted_enabled: merged.receiptExtractedEnabled,
         receipt_matched_enabled: merged.receiptMatchedEnabled,
+        missing_underlag_enabled: merged.missingUnderlagEnabled,
       },
       { onConflict: 'user_id' }
     )
diff --git a/extensions/general/push-notifications/notification-scheduler.ts b/extensions/general/push-notifications/notification-scheduler.ts
index 94cdb0ca..e4ba5bc6 100644
--- a/extensions/general/push-notifications/notification-scheduler.ts
+++ b/extensions/general/push-notifications/notification-scheduler.ts
@@ -16,6 +16,7 @@ import {
   createTaxDeadlinePayload,
   createInvoiceOverduePayload,
   createInvoiceDuePayload,
+  createMissingUnderlagPayload,
 } from './payload-builders'
 
 /**
@@ -208,3 +209,92 @@ export async function sendInvoiceNotifications(
 
   return { sent, skipped }
 }
+
+/**
+ * Source types that require supporting documents (underlag).
+ */
+const NEEDS_ATTACHMENT_SOURCE_TYPES = [
+  'manual',
+  'bank_transaction',
+  'supplier_invoice_registered',
+  'supplier_invoice_paid',
+  'supplier_invoice_cash_payment',
+  'import',
+]
+
+/**
+ * Send missing underlag notifications.
+ * Checks all users for posted journal entries without attached documents.
+ * Deduplicates via the 'missing-underlag-weekly' tag on the notification payload.
+ */
+export async function sendMissingUnderlagNotifications(
+  supabase: SupabaseClient
+): Promise<{ sent: number; skipped: number }> {
+  let sent = 0
+  let skipped = 0
+
+  // Get all users who have posted entries with source types that need docs
+  const { data: entries } = await supabase
+    .from('journal_entries')
+    .select('id, user_id')
+    .eq('status', 'posted')
+    .in('source_type', NEEDS_ATTACHMENT_SOURCE_TYPES)
+
+  if (!entries || entries.length === 0) {
+    return { sent: 0, skipped: 0 }
+  }
+
+  // Get all document_attachments linked to journal entries
+  const { data: attachments } = await supabase
+    .from('document_attachments')
+    .select('journal_entry_id')
+    .eq('is_current_version', true)
+    .not('journal_entry_id', 'is', null)
+
+  const entriesWithDocs = new Set(
+    (attachments || []).map((a) => a.journal_entry_id)
+  )
+
+  // Group missing counts by user
+  const userMissingCounts = new Map<string, number>()
+  for (const entry of entries) {
+    if (!entriesWithDocs.has(entry.id)) {
+      userMissingCounts.set(
+        entry.user_id,
+        (userMissingCounts.get(entry.user_id) || 0) + 1
+      )
+    }
+  }
+
+  for (const [userId, count] of userMissingCounts) {
+    // Check user setting
+    const { data: settings } = await supabase
+      .from('notification_settings')
+      .select('missing_underlag_enabled')
+      .eq('user_id', userId)
+      .single()
+
+    if (settings && settings.missing_underlag_enabled === false) {
+      skipped++
+      continue
+    }
+
+    const payload = createMissingUnderlagPayload(count)
+
+    const result = await sendNotificationToUser(
+      supabase,
+      userId,
+      payload,
+      'missing_underlag',
+      'weekly-check'
+    )
+
+    if (result.sent) {
+      sent++
+    } else {
+      skipped++
+    }
+  }
+
+  return { sent, skipped }
+}
diff --git a/extensions/general/push-notifications/payload-builders.ts b/extensions/general/push-notifications/payload-builders.ts
index 36ca5359..a697ec3b 100644
--- a/extensions/general/push-notifications/payload-builders.ts
+++ b/extensions/general/push-notifications/payload-builders.ts
@@ -114,6 +114,24 @@ export function createReceiptMatchedPayload(
   }
 }
 
+// ============================================================
+// Missing underlag payload
+// ============================================================
+
+export function createMissingUnderlagPayload(count: number): NotificationPayload {
+  return {
+    title: 'Saknade underlag',
+    body: `${count} verifikation(er) saknar underlag. Bifoga for att uppfylla bokforingslagen.`,
+    icon: '/icons/icon-192.png',
+    badge: '/icons/badge-72.png',
+    tag: 'missing-underlag-weekly',
+    data: {
+      url: '/bookkeeping?missingUnderlag=true',
+      type: 'missing_underlag',
+    },
+  }
+}
+
 // ============================================================
 // Cron-based payloads (moved from lib/push/web-push.ts)
 // ============================================================
diff --git a/lib/errors/get-error-message.ts b/lib/errors/get-error-message.ts
new file mode 100644
index 00000000..2909d67e
--- /dev/null
+++ b/lib/errors/get-error-message.ts
@@ -0,0 +1,200 @@
+/**
+ * Maps raw errors to user-friendly Swedish messages.
+ *
+ * Priority chain:
+ * 1. Zod validation field errors
+ * 2. Postgres error code map
+ * 3. HTTP status code map
+ * 4. Context-specific fallback
+ * 5. Generic fallback
+ */
+
+type ErrorContext =
+  | 'invoice'
+  | 'supplier_invoice'
+  | 'customer'
+  | 'supplier'
+  | 'transaction'
+  | 'journal_entry'
+  | 'settings'
+  | 'auth'
+
+interface GetErrorMessageOptions {
+  context?: ErrorContext
+  statusCode?: number
+}
+
+// Postgres error codes -> Swedish messages
+const POSTGRES_ERROR_MAP: Record<string, string> = {
+  '23505': 'En post med samma uppgifter finns redan.',
+  '23503': 'Posten kan inte ändras eftersom den refereras av annan data.',
+  '23502': 'Ett obligatoriskt fält saknas.',
+  '42501': 'Du har inte behörighet att utföra denna åtgärd.',
+  '42P01': 'Resursen kunde inte hittas.',
+  '23514': 'Värdet uppfyller inte de tillåtna kraven.',
+  '40001': 'En annan ändring pågick samtidigt. Försök igen.',
+  '40P01': 'En konflikt uppstod. Försök igen.',
+  '22P02': 'Ogiltigt värde angavs.',
+  '22003': 'Värdet är utanför tillåtet intervall.',
+}
+
+// HTTP status codes -> Swedish messages
+const HTTP_STATUS_MAP: Record<number, string> = {
+  400: 'Förfrågan innehåller ogiltiga uppgifter.',
+  401: 'Din session har gått ut. Logga in igen.',
+  403: 'Du har inte behörighet att utföra denna åtgärd.',
+  404: 'Resursen kunde inte hittas.',
+  409: 'En konflikt uppstod. Ladda om sidan och försök igen.',
+  422: 'Uppgifterna kunde inte bearbetas. Kontrollera fälten och försök igen.',
+  429: 'För många förfrågningar. Vänta en stund och försök igen.',
+  500: 'Ett oväntat serverfel uppstod. Försök igen senare.',
+  502: 'Servern är tillfälligt otillgänglig. Försök igen om en stund.',
+  503: 'Tjänsten är tillfälligt otillgänglig. Försök igen om en stund.',
+}
+
+// Context-specific fallbacks
+const CONTEXT_FALLBACKS: Record<ErrorContext, string> = {
+  invoice: 'Kunde inte hantera fakturan. Försök igen.',
+  supplier_invoice: 'Kunde inte hantera leverantörsfakturan. Försök igen.',
+  customer: 'Kunde inte hantera kunden. Försök igen.',
+  supplier: 'Kunde inte hantera leverantören. Försök igen.',
+  transaction: 'Kunde inte hantera transaktionen. Försök igen.',
+  journal_entry: 'Kunde inte hantera verifikationen. Försök igen.',
+  settings: 'Kunde inte spara inställningarna. Försök igen.',
+  auth: 'Ett fel uppstod vid inloggningen. Försök igen.',
+}
+
+const GENERIC_FALLBACK = 'Något gick fel. Försök igen.'
+
+/**
+ * Simple heuristic to detect already-translated Swedish messages.
+ * If the message contains common Swedish words/patterns, pass it through.
+ */
+function isSwedishUserMessage(message: string): boolean {
+  const swedishPatterns = [
+    /kunde inte/i,
+    /försök igen/i,
+    /ogiltigt?/i,
+    /saknas/i,
+    /måste/i,
+    /redan finns/i,
+    /gick fel/i,
+    /behörighet/i,
+    /session/i,
+    /förfrågan/i,
+    /obligatorisk/i,
+  ]
+  return swedishPatterns.some((p) => p.test(message))
+}
+
+/**
+ * Extract a user-friendly message from a Zod validation error shape.
+ * Returns null if the error is not a Zod error.
+ */
+function tryParseZodErrors(error: unknown): string | null {
+  if (typeof error !== 'object' || error === null) return null
+
+  const obj = error as Record<string, unknown>
+
+  // Check for Zod-style field errors: { fieldName: ["message"] } or { issues: [...] }
+  if (Array.isArray(obj.issues)) {
+    const issues = obj.issues as Array<{ message?: string; path?: string[] }>
+    const messages = issues
+      .slice(0, 3)
+      .map((issue) => {
+        const field = issue.path?.join('.') || ''
+        const msg = issue.message || 'ogiltigt värde'
+        return field ? `${field}: ${msg}` : msg
+      })
+    if (messages.length > 0) return messages.join('. ')
+  }
+
+  // Check for { errors: { field: ["msg"] } } shape from validateBody
+  if (typeof obj.errors === 'object' && obj.errors !== null) {
+    const fieldErrors = obj.errors as Record<string, string[]>
+    const messages: string[] = []
+    for (const [field, msgs] of Object.entries(fieldErrors)) {
+      if (Array.isArray(msgs) && msgs.length > 0) {
+        messages.push(`${field}: ${msgs[0]}`)
+      }
+      if (messages.length >= 3) break
+    }
+    if (messages.length > 0) return messages.join('. ')
+  }
+
+  return null
+}
+
+/**
+ * Get a user-friendly Swedish error message from a raw error.
+ *
+ * @param error - The raw error. Can be an API response body (object), Error instance, string, or unknown.
+ * @param options - Optional context and HTTP status code.
+ */
+export function getErrorMessage(
+  error: unknown,
+  options: GetErrorMessageOptions = {}
+): string {
+  const { context, statusCode } = options
+
+  // 1. If it's a string, check if it's already Swedish
+  if (typeof error === 'string' && error.trim()) {
+    if (isSwedishUserMessage(error)) return error
+  }
+
+  // 2. If it's an object, try various parsing strategies
+  if (typeof error === 'object' && error !== null) {
+    const obj = error as Record<string, unknown>
+
+    // Try Zod validation errors
+    const zodMessage = tryParseZodErrors(obj)
+    if (zodMessage) return zodMessage
+
+    // Try Postgres error code
+    if (typeof obj.code === 'string' && POSTGRES_ERROR_MAP[obj.code]) {
+      return POSTGRES_ERROR_MAP[obj.code]
+    }
+
+    // Try error.message if it's already a good Swedish message
+    if (typeof obj.error === 'string' && obj.error.trim()) {
+      if (isSwedishUserMessage(obj.error)) return obj.error
+    }
+
+    if (typeof obj.message === 'string' && obj.message.trim()) {
+      if (isSwedishUserMessage(obj.message)) return obj.message
+    }
+  }
+
+  // 3. Error instance
+  if (error instanceof Error && error.message.trim()) {
+    if (isSwedishUserMessage(error.message)) return error.message
+  }
+
+  // 4. HTTP status code map
+  if (statusCode && HTTP_STATUS_MAP[statusCode]) {
+    return HTTP_STATUS_MAP[statusCode]
+  }
+
+  // 5. Context-specific fallback
+  if (context && CONTEXT_FALLBACKS[context]) {
+    return CONTEXT_FALLBACKS[context]
+  }
+
+  // 6. Generic fallback
+  return GENERIC_FALLBACK
+}
+
+/**
+ * Helper that parses a Response body and returns a user-friendly error message.
+ */
+export async function getResponseErrorMessage(
+  response: Response,
+  context?: ErrorContext
+): Promise<string> {
+  try {
+    const body = await response.json()
+    return getErrorMessage(body, { context, statusCode: response.status })
+  } catch {
+    return getErrorMessage(null, { context, statusCode: response.status })
+  }
+}
diff --git a/lib/hooks/use-unsaved-changes.ts b/lib/hooks/use-unsaved-changes.ts
new file mode 100644
index 00000000..176dcbd9
--- /dev/null
+++ b/lib/hooks/use-unsaved-changes.ts
@@ -0,0 +1,22 @@
+'use client'
+
+import { useEffect } from 'react'
+
+/**
+ * Attaches a `beforeunload` event listener when the form has unsaved changes.
+ * This guards against browser close, tab close, and page refresh.
+ *
+ * Does NOT guard in-app Next.js navigation (App Router has no supported mechanism).
+ */
+export function useUnsavedChanges(isDirty: boolean) {
+  useEffect(() => {
+    if (!isDirty) return
+
+    const handler = (e: BeforeUnloadEvent) => {
+      e.preventDefault()
+    }
+
+    window.addEventListener('beforeunload', handler)
+    return () => window.removeEventListener('beforeunload', handler)
+  }, [isDirty])
+}
diff --git a/types/index.ts b/types/index.ts
index 1b02e726..0aed19e5 100644
--- a/types/index.ts
+++ b/types/index.ts
@@ -1220,6 +1220,7 @@ export type NotificationType =
   | 'receipt_extracted'
   | 'receipt_matched'
   | 'invoice_sent'
+  | 'missing_underlag'
 
 // Notification log entry
 export interface NotificationLog {