diff --git a/app/(dashboard)/import/page.tsx b/app/(dashboard)/import/page.tsx
index b707be73..851835ce 100644
--- a/app/(dashboard)/import/page.tsx
+++ b/app/(dashboard)/import/page.tsx
@@ -322,6 +322,7 @@ function SIEImportWizard() {
   const [step, setStep] = useState<ImportWizardStep>('upload')
   const [isLoading, setIsLoading] = useState(false)
   const [error, setError] = useState<string | null>(null)
+  const [errorType, setErrorType] = useState<'duplicate' | 'duplicate_period' | 'validation' | 'parse' | undefined>()
 
   const [file, setFile] = useState<File | null>(null)
   const [, setParsed] = useState<ParsedSIEFile | null>(null)
@@ -345,6 +346,7 @@ function SIEImportWizard() {
   const handleFileSelect = useCallback(async (selectedFile: File) => {
     setFile(selectedFile)
     setError(null)
+    setErrorType(undefined)
     setIsLoading(true)
 
     try {
@@ -360,10 +362,13 @@ function SIEImportWizard() {
 
       if (!res.ok) {
         if (data.error === 'duplicate' || data.error === 'duplicate_period') {
+          setErrorType(data.error)
           setError(data.message)
         } else if (data.error === 'validation') {
+          setErrorType('validation')
           setError(`${data.message}: ${data.errors?.join(', ') || 'Unknown validation error'}`)
         } else {
+          setErrorType('parse')
           setError(data.error || 'Failed to parse file')
         }
         return
@@ -450,30 +455,38 @@ function SIEImportWizard() {
 
       toast({ title: 'Konton skapade', description: `${data.created} nya konton har lagts till i din kontoplan` })
 
-      if (file) {
-        const formData = new FormData()
-        formData.append('file', file)
-
-        const parseRes = await fetch('/api/import/sie/parse', { method: 'POST', body: formData })
-        const parseData = await parseRes.json()
-
-        if (parseRes.ok) {
-          setMappings(parseData.mappings)
-          setPreview(parseData.preview)
-
-          const accountsRes = await fetch('/api/bookkeeping/accounts')
-          if (accountsRes.ok) {
-            const accountsData = await accountsRes.json()
-            setBasAccounts(accountsData.data || [])
-          }
+      // Optimistically update mappings: mark created accounts as self-mapped
+      const createdSet = new Set(missingAccounts.map(a => a.number))
+      setMappings(prev => prev.map(m =>
+        !m.targetAccount && createdSet.has(m.sourceAccount)
+          ? { ...m, targetAccount: m.sourceAccount, targetName: m.sourceName, confidence: 1.0 }
+          : m
+      ))
+      setPreview(prev => {
+        if (!prev) return prev
+        const newMapped = prev.mappingStatus.mapped + createdSet.size
+        return {
+          ...prev,
+          mappingStatus: {
+            ...prev.mappingStatus,
+            mapped: newMapped,
+            unmapped: Math.max(0, prev.mappingStatus.unmapped - createdSet.size),
+          },
         }
+      })
+
+      // Also refresh BAS accounts list
+      const accountsRes = await fetch('/api/bookkeeping/accounts')
+      if (accountsRes.ok) {
+        const accountsData = await accountsRes.json()
+        setBasAccounts(accountsData.data || [])
       }
     } catch (err) {
       toast({ title: 'Kunde inte skapa konton', description: err instanceof Error ? err.message : 'Försök igen.', variant: 'destructive' })
     } finally {
       setIsCreatingAccounts(false)
     }
-  }, [missingAccounts, file, toast])
+  }, [missingAccounts, toast])
 
   const handleExecuteImport = useCallback(async (options: ImportExecuteOptions) => {
     if (!file) { setError('No file selected'); return }
@@ -491,6 +504,10 @@ function SIEImportWizard() {
       const data = await res.json()
 
       if (!res.ok) {
+        if (data.error === 'duplicate') {
+          setError(data.message || 'Denna fil har redan importerats')
+          return
+        }
         if (data.result) { setImportResult(data.result) } else { setError(data.error || 'Import failed'); return }
       } else {
         setImportResult(data.result)
@@ -513,7 +530,7 @@ function SIEImportWizard() {
 
   const handleNewImport = () => {
     setStep('upload'); setFile(null); setParsed(null); setMappings([])
-    setPreview(null); setIssues([]); setImportResult(null); setError(null)
+    setPreview(null); setIssues([]); setImportResult(null); setError(null); setErrorType(undefined)
     setSieAccounts([]); setIsCreatingAccounts(false)
   }
 
@@ -540,7 +557,7 @@ function SIEImportWizard() {
         </CardContent>
       </Card>
 
-      {step === 'upload' && <SIEUploadStep onFileSelect={handleFileSelect} isLoading={isLoading} error={error} />}
+      {step === 'upload' && <SIEUploadStep onFileSelect={handleFileSelect} isLoading={isLoading} error={error} errorType={errorType} />}
       {step === 'preview' && preview && (
         <SIEPreviewStep preview={preview} issues={issues} missingAccounts={missingAccounts}
           onCreateAccounts={handleCreateAccounts} isCreatingAccounts={isCreatingAccounts}
diff --git a/app/api/import/sie/execute/route.ts b/app/api/import/sie/execute/route.ts
index 9d9b7f74..2967f1ff 100644
--- a/app/api/import/sie/execute/route.ts
+++ b/app/api/import/sie/execute/route.ts
@@ -4,7 +4,7 @@ import { NextResponse } from 'next/server'
 import { requireCompanyId } from '@/lib/company/context'
 import { parseSIEFile, detectEncoding, decodeBuffer } from '@/lib/import/sie-parser'
 import { suggestMappings } from '@/lib/import/account-mapper'
-import { executeSIEImport } from '@/lib/import/sie-import'
+import { executeSIEImport, checkDuplicateImport } from '@/lib/import/sie-import'
 import { BAS_REFERENCE } from '@/lib/bookkeeping/bas-data'
 import { getBASReference } from '@/lib/bookkeeping/bas-reference'
 import type { AccountMapping, SIEAccountMappingRecord } from '@/lib/import/types'
@@ -56,6 +56,15 @@ export async function POST(request: Request) {
     // Parse the SIE file
     const parsed = parseSIEFile(content)
 
+    // Check for duplicate import before doing any work
+    const duplicate = await checkDuplicateImport(supabase, companyId, content)
+    if (duplicate) {
+      return NextResponse.json({
+        error: 'duplicate',
+        message: `Denna fil har redan importerats ${duplicate.imported_at ? new Date(duplicate.imported_at).toLocaleDateString('sv-SE') : ''}`.trim(),
+      }, { status: 409 })
+    }
+
     // Get mappings - either from request or generate new ones
     let mappings: AccountMapping[]
 
diff --git a/components/import/SIEUploadStep.tsx b/components/import/SIEUploadStep.tsx
index 20db96e5..82c61bfe 100644
--- a/components/import/SIEUploadStep.tsx
+++ b/components/import/SIEUploadStep.tsx
@@ -16,9 +16,10 @@ interface SIEUploadStepProps {
   onFileSelect: (file: File) => void
   isLoading: boolean
   error: string | null
+  errorType?: 'duplicate' | 'duplicate_period' | 'validation' | 'parse'
 }
 
-export default function SIEUploadStep({ onFileSelect, isLoading, error }: SIEUploadStepProps) {
+export default function SIEUploadStep({ onFileSelect, isLoading, error, errorType }: SIEUploadStepProps) {
   const [isDragging, setIsDragging] = useState(false)
   const [selectedFile, setSelectedFile] = useState<File | null>(null)
   const [loadingPhase, setLoadingPhase] = useState(0)
@@ -161,7 +162,11 @@ export default function SIEUploadStep({ onFileSelect, isLoading, error }: SIEUpl
             <div className="mt-4 p-4 bg-destructive/10 border border-destructive/20 rounded-lg flex gap-3">
               <AlertCircle className="h-5 w-5 text-destructive flex-shrink-0 mt-0.5" />
               <div>
-                <p className="font-medium text-destructive">Kunde inte läsa filen</p>
+                <p className="font-medium text-destructive">
+                  {errorType === 'duplicate' || errorType === 'duplicate_period'
+                    ? 'Filen har redan importerats'
+                    : 'Kunde inte läsa filen'}
+                </p>
                 <p className="text-sm text-muted-foreground">{error}</p>
               </div>
             </div>
diff --git a/lib/import/sie-import.ts b/lib/import/sie-import.ts
index 2120a598..db7ac3f4 100644
--- a/lib/import/sie-import.ts
+++ b/lib/import/sie-import.ts
@@ -1250,20 +1250,72 @@ export async function executeSIEImport(
     const accountMap = mappingsToMap(mappings)
 
     // Ensure all mapped target accounts exist in chart_of_accounts.
-    // The mapping contains every account referenced in the SIE file; accounts
-    // that were not seeded during onboarding need to be created here so that
-    // journal entry lines can link to them via account_id.
-    const seenTargets = new Set<string>()
-    for (const mapping of mappings) {
-      if (mapping.targetAccount && !seenTargets.has(mapping.targetAccount)) {
-        seenTargets.add(mapping.targetAccount)
-        await ensureAccountExists(
-          supabase,
-          companyId,
-          userId,
-          mapping.targetAccount,
-          mapping.targetName
-        )
+    // Uses a single batch query + batch insert instead of per-account round trips.
+    const targetAccounts = [...new Set(
+      mappings.filter(m => m.targetAccount).map(m => m.targetAccount!)
+    )]
+
+    if (targetAccounts.length > 0) {
+      const { data: existing } = await supabase
+        .from('chart_of_accounts')
+        .select('account_number')
+        .eq('company_id', companyId)
+        .in('account_number', targetAccounts)
+
+      const existingSet = new Set((existing || []).map(a => a.account_number))
+      const missing = targetAccounts.filter(num => !existingSet.has(num))
+
+      if (missing.length > 0) {
+        const targetNameMap = new Map<string, string>()
+        for (const m of mappings) {
+          if (m.targetAccount) targetNameMap.set(m.targetAccount, m.targetName || m.sourceName)
+        }
+
+        const inserts = missing.map(num => {
+          const basRef = getBASReference(num)
+          if (basRef) {
+            return {
+              user_id: userId,
+              company_id: companyId,
+              account_number: num,
+              account_name: basRef.account_name,
+              account_class: basRef.account_class,
+              account_group: basRef.account_group,
+              account_type: basRef.account_type,
+              normal_balance: basRef.normal_balance,
+              sru_code: basRef.sru_code ?? computeSRUCode(num),
+              k2_excluded: basRef.k2_excluded,
+              plan_type: 'full_bas' as const,
+              is_active: true,
+              is_system_account: false,
+            }
+          }
+          const classNum = parseInt(num.charAt(0), 10)
+          const group = num.substring(0, 2)
+          const accountType = classNum === 1 ? 'asset'
+            : classNum === 2 ? (group === '21' ? 'untaxed_reserves' : (group === '20' ? 'equity' : 'liability'))
+            : classNum === 3 ? 'revenue' : 'expense'
+          return {
+            user_id: userId,
+            company_id: companyId,
+            account_number: num,
+            account_name: targetNameMap.get(num) || `Konto ${num}`,
+            account_class: classNum,
+            account_group: group,
+            account_type: accountType,
+            normal_balance: classNum <= 1 || classNum >= 4 ? 'debit' : 'credit',
+            sru_code: computeSRUCode(num),
+            plan_type: 'full_bas' as const,
+            is_active: true,
+            is_system_account: false,
+          }
+        })
+
+        const { error: insertError } = await supabase.from('chart_of_accounts').insert(inserts)
+        if (insertError && !insertError.message.includes('duplicate')) {
+          result.errors.push(`Failed to create accounts: ${insertError.message}`)
+          return result
+        }
       }
     }