diff --git a/app/Console/Commands/ResetDemoAccountCommand.php b/app/Console/Commands/ResetDemoAccountCommand.php
index 324e9e8f..8506575d 100644
--- a/app/Console/Commands/ResetDemoAccountCommand.php
+++ b/app/Console/Commands/ResetDemoAccountCommand.php
@@ -468,8 +468,6 @@ class ResetDemoAccountCommand extends Command
                         $currentDate->addDay();
                     }
                     break;
-                case BudgetPeriodType::Custom:
-                    break;
             }
 
             $iteration++;
diff --git a/app/Enums/BudgetPeriodType.php b/app/Enums/BudgetPeriodType.php
index d4c3f08e..1765d0de 100644
--- a/app/Enums/BudgetPeriodType.php
+++ b/app/Enums/BudgetPeriodType.php
@@ -7,7 +7,6 @@ enum BudgetPeriodType: string
     case Monthly = 'monthly';
     case Weekly = 'weekly';
     case Biweekly = 'biweekly';
-    case Custom = 'custom';
 
     public function label(): string
     {
@@ -15,7 +14,6 @@ enum BudgetPeriodType: string
             self::Monthly => 'Monthly',
             self::Weekly => 'Weekly',
             self::Biweekly => 'Bi-weekly',
-            self::Custom => 'Custom',
         };
     }
 }
diff --git a/app/Http/Controllers/BudgetController.php b/app/Http/Controllers/BudgetController.php
index c64e2564..c87f3de7 100644
--- a/app/Http/Controllers/BudgetController.php
+++ b/app/Http/Controllers/BudgetController.php
@@ -119,7 +119,6 @@ class BudgetController extends Controller
             $budget = $request->user()->budgets()->create([
                 'name' => $request->name,
                 'period_type' => $request->period_type,
-                'period_duration' => $request->period_duration,
                 'period_start_day' => $request->period_start_day,
                 'category_id' => $request->category_id,
                 'label_id' => $request->label_id,
@@ -145,7 +144,6 @@ class BudgetController extends Controller
             $budget->update($request->only([
                 'name',
                 'period_type',
-                'period_duration',
                 'period_start_day',
                 'category_id',
                 'label_id',
diff --git a/app/Http/Requests/StoreBudgetRequest.php b/app/Http/Requests/StoreBudgetRequest.php
index f44a0997..9fdd3bb8 100644
--- a/app/Http/Requests/StoreBudgetRequest.php
+++ b/app/Http/Requests/StoreBudgetRequest.php
@@ -21,7 +21,6 @@ class StoreBudgetRequest extends FormRequest
         return [
             'name' => ['required', 'string', 'max:255'],
             'period_type' => ['required', Rule::enum(BudgetPeriodType::class)],
-            'period_duration' => ['nullable', 'integer', 'min:1', 'max:365'],
             'period_start_day' => ['nullable', 'integer', 'min:0', 'max:31'],
             'category_id' => ['nullable', Rule::exists('categories', 'id')->where('user_id', $userId)],
             'label_id' => ['nullable', Rule::exists('labels', 'id')->where('user_id', $userId)],
diff --git a/app/Http/Requests/UpdateBudgetRequest.php b/app/Http/Requests/UpdateBudgetRequest.php
index e06420d8..7cd5dca7 100644
--- a/app/Http/Requests/UpdateBudgetRequest.php
+++ b/app/Http/Requests/UpdateBudgetRequest.php
@@ -21,7 +21,6 @@ class UpdateBudgetRequest extends FormRequest
         return [
             'name' => ['sometimes', 'string', 'max:255'],
             'period_type' => ['sometimes', Rule::enum(BudgetPeriodType::class)],
-            'period_duration' => ['nullable', 'integer', 'min:1', 'max:365'],
             'period_start_day' => ['nullable', 'integer', 'min:0', 'max:31'],
             'category_id' => ['nullable', Rule::exists('categories', 'id')->where('user_id', $userId)],
             'label_id' => ['nullable', Rule::exists('labels', 'id')->where('user_id', $userId)],
diff --git a/app/Models/Budget.php b/app/Models/Budget.php
index 1ca7505c..9d87dde5 100644
--- a/app/Models/Budget.php
+++ b/app/Models/Budget.php
@@ -23,7 +23,6 @@ class Budget extends Model
         'user_id',
         'name',
         'period_type',
-        'period_duration',
         'period_start_day',
         'category_id',
         'label_id',
@@ -35,7 +34,6 @@ class Budget extends Model
         return [
             'period_type' => BudgetPeriodType::class,
             'rollover_type' => RolloverType::class,
-            'period_duration' => 'integer',
             'period_start_day' => 'integer',
         ];
     }
diff --git a/app/Services/BudgetPeriodService.php b/app/Services/BudgetPeriodService.php
index 50681d7e..76628776 100644
--- a/app/Services/BudgetPeriodService.php
+++ b/app/Services/BudgetPeriodService.php
@@ -80,17 +80,6 @@ class BudgetPeriodService
                 $endDate = $startDate->copy()->addWeeks(2)->subDay();
                 break;
 
-            case BudgetPeriodType::Custom:
-                $duration = $budget->period_duration ?? 30;
-                $startDate->day($budget->period_start_day ?? 1);
-                if ($startDate > $referenceDate) {
-                    $startDate->subDays($duration);
-                }
-                $endDate = $startDate->copy()->addDays($duration)->subDay();
-                break;
-
-            default:
-                $endDate = $startDate->copy()->addMonth()->subDay();
         }
 
         return [$startDate, $endDate];
diff --git a/database/factories/BudgetFactory.php b/database/factories/BudgetFactory.php
index 4611ce51..51552e19 100644
--- a/database/factories/BudgetFactory.php
+++ b/database/factories/BudgetFactory.php
@@ -23,7 +23,6 @@ class BudgetFactory extends Factory
             'user_id' => User::factory(),
             'name' => fake()->words(2, true).' Budget',
             'period_type' => fake()->randomElement(BudgetPeriodType::cases()),
-            'period_duration' => null,
             'period_start_day' => 1,
         ];
     }
@@ -43,13 +42,4 @@ class BudgetFactory extends Factory
             'period_start_day' => fake()->numberBetween(0, 6),
         ]);
     }
-
-    public function custom(): static
-    {
-        return $this->state(fn (array $attributes) => [
-            'period_type' => BudgetPeriodType::Custom,
-            'period_duration' => fake()->numberBetween(7, 90),
-            'period_start_day' => fake()->numberBetween(1, 28),
-        ]);
-    }
 }
diff --git a/database/migrations/2026_05_05_132023_convert_custom_budgets_to_monthly.php b/database/migrations/2026_05_05_132023_convert_custom_budgets_to_monthly.php
new file mode 100644
index 00000000..10335388
--- /dev/null
+++ b/database/migrations/2026_05_05_132023_convert_custom_budgets_to_monthly.php
@@ -0,0 +1,23 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Support\Facades\DB;
+
+return new class extends Migration
+{
+    public function up(): void
+    {
+        DB::table('budgets')
+            ->where('period_type', 'custom')
+            ->update([
+                'period_type' => 'monthly',
+                'period_duration' => null,
+                'period_start_day' => 1,
+            ]);
+    }
+
+    public function down(): void
+    {
+        // Irreversible: original period_type/duration cannot be recovered.
+    }
+};
diff --git a/resources/js/components/budgets/create-budget-dialog.tsx b/resources/js/components/budgets/create-budget-dialog.tsx
index e30c2929..546c561b 100644
--- a/resources/js/components/budgets/create-budget-dialog.tsx
+++ b/resources/js/components/budgets/create-budget-dialog.tsx
@@ -52,7 +52,6 @@ export function CreateBudgetDialog({
     const [open, setOpen] = useState(false);
     const [name, setName] = useState('');
     const [periodType, setPeriodType] = useState<BudgetPeriodType>('monthly');
-    const [periodDuration, setPeriodDuration] = useState<number | null>(null);
     const [periodStartDay, setPeriodStartDay] = useState<number>(1);
     const [selectedCategoryId, setSelectedCategoryId] = useState<string>('');
     const [selectedLabelId, setSelectedLabelId] = useState<string>('');
@@ -89,7 +88,6 @@ export function CreateBudgetDialog({
             {
                 name,
                 period_type: periodType,
-                period_duration: periodDuration,
                 period_start_day: periodStartDay,
                 category_id: selectedCategoryId || null,
                 label_id: selectedLabelId || null,
@@ -101,7 +99,6 @@ export function CreateBudgetDialog({
                     setOpen(false);
                     setName('');
                     setPeriodType('monthly');
-                    setPeriodDuration(null);
                     setPeriodStartDay(1);
                     setSelectedCategoryId('');
                     setSelectedLabelId('');
@@ -184,29 +181,6 @@ export function CreateBudgetDialog({
                             </Select>
                         </div>
 
-                        {periodType === 'custom' && (
-                            <div className="space-y-2">
-                                <UILabel htmlFor="period-duration">
-                                    {__('Period Duration (days)')}
-                                </UILabel>
-                                <Input
-                                    id="period-duration"
-                                    type="number"
-                                    min="1"
-                                    max="365"
-                                    value={periodDuration ?? ''}
-                                    onChange={(e) =>
-                                        setPeriodDuration(
-                                            e.target.value
-                                                ? parseInt(e.target.value)
-                                                : null,
-                                        )
-                                    }
-                                    required={periodType === 'custom'}
-                                />
-                            </div>
-                        )}
-
                         <div className="space-y-2">
                             <UILabel htmlFor="period-start-day">
                                 {periodType === 'monthly'
diff --git a/resources/js/components/budgets/edit-budget-dialog.tsx b/resources/js/components/budgets/edit-budget-dialog.tsx
index 5855d481..053eafa1 100644
--- a/resources/js/components/budgets/edit-budget-dialog.tsx
+++ b/resources/js/components/budgets/edit-budget-dialog.tsx
@@ -50,9 +50,6 @@ export function EditBudgetDialog({
     const [periodType, setPeriodType] = useState<BudgetPeriodType>(
         budget.period_type as BudgetPeriodType,
     );
-    const [periodDuration, setPeriodDuration] = useState<number | null>(
-        budget.period_duration,
-    );
     const [periodStartDay, setPeriodStartDay] = useState<number>(
         budget.period_start_day || 1,
     );
@@ -68,7 +65,6 @@ export function EditBudgetDialog({
         if (open && budget) {
             setName(budget.name);
             setPeriodType(budget.period_type as BudgetPeriodType);
-            setPeriodDuration(budget.period_duration);
             setPeriodStartDay(budget.period_start_day || 1);
             setAllocatedAmount(currentPeriod.allocated_amount);
             setRolloverType(budget.rollover_type as RolloverType);
@@ -84,7 +80,6 @@ export function EditBudgetDialog({
             {
                 name,
                 period_type: periodType,
-                period_duration: periodDuration,
                 period_start_day: periodStartDay,
                 allocated_amount: allocatedAmount,
                 rollover_type: rolloverType,
@@ -150,31 +145,6 @@ export function EditBudgetDialog({
                             </div>
                         </div>
 
-                        {periodType === 'custom' && (
-                            <div className="space-y-2">
-                                <Label htmlFor="period-duration">
-                                    {__('Period Duration (days)')}
-                                </Label>
-                                <Input
-                                    disabled
-                                    id="period-duration"
-                                    type="number"
-                                    min="1"
-                                    max="365"
-                                    className="mt-1"
-                                    value={periodDuration ?? ''}
-                                    onChange={(e) =>
-                                        setPeriodDuration(
-                                            e.target.value
-                                                ? parseInt(e.target.value)
-                                                : null,
-                                        )
-                                    }
-                                    required={periodType === 'custom'}
-                                />
-                            </div>
-                        )}
-
                         <div className="space-y-2">
                             <Label htmlFor="period-start-day">
                                 {periodType === 'monthly'
diff --git a/resources/js/types/budget.ts b/resources/js/types/budget.ts
index 1eb82a0d..71cc335a 100644
--- a/resources/js/types/budget.ts
+++ b/resources/js/types/budget.ts
@@ -4,12 +4,7 @@ import { Label } from './label';
 import { Transaction } from './transaction';
 import { UUID } from './uuid';
 
-export const BUDGET_PERIOD_TYPES = [
-    'monthly',
-    'weekly',
-    'biweekly',
-    'custom',
-] as const;
+export const BUDGET_PERIOD_TYPES = ['monthly', 'weekly', 'biweekly'] as const;
 
 export type BudgetPeriodType = (typeof BUDGET_PERIOD_TYPES)[number];
 
@@ -22,7 +17,6 @@ export interface Budget {
     user_id: UUID;
     name: string;
     period_type: BudgetPeriodType;
-    period_duration: number | null;
     period_start_day: number | null;
     category_id: UUID | null;
     label_id: UUID | null;
@@ -70,7 +64,6 @@ export function getBudgetPeriodTypeLabel(type: BudgetPeriodType): string {
         monthly: __('Monthly'),
         weekly: __('Weekly'),
         biweekly: __('Bi-weekly'),
-        custom: __('Custom'),
     };
     return labels[type];
 }
diff --git a/tests/Feature/BudgetPeriodServiceTest.php b/tests/Feature/BudgetPeriodServiceTest.php
new file mode 100644
index 00000000..361f8d69
--- /dev/null
+++ b/tests/Feature/BudgetPeriodServiceTest.php
@@ -0,0 +1,74 @@
+<?php
+
+use App\Enums\BudgetPeriodType;
+use App\Models\Budget;
+use App\Models\BudgetPeriod;
+use App\Models\User;
+use App\Services\BudgetPeriodService;
+use Carbon\Carbon;
+
+afterEach(function () {
+    Carbon::setTestNow();
+});
+
+test('generatePeriod advances monthly periods to next month', function () {
+    Carbon::setTestNow(Carbon::parse('2026-06-02 09:00:00'));
+
+    $user = User::factory()->create(['onboarded_at' => now()]);
+    $budget = Budget::factory()->create([
+        'user_id' => $user->id,
+        'period_type' => BudgetPeriodType::Monthly,
+        'period_start_day' => 1,
+    ]);
+
+    BudgetPeriod::factory()->create([
+        'budget_id' => $budget->id,
+        'start_date' => '2026-05-01',
+        'end_date' => '2026-05-31',
+        'allocated_amount' => 10000,
+    ]);
+
+    $next = app(BudgetPeriodService::class)->generatePeriod($budget);
+
+    expect($next->start_date->toDateString())->toBe('2026-06-01');
+    expect($next->end_date->toDateString())->toBe('2026-06-30');
+});
+
+test('generatePeriod advances weekly periods to next week', function () {
+    Carbon::setTestNow(Carbon::parse('2026-05-12 09:00:00'));
+
+    $user = User::factory()->create(['onboarded_at' => now()]);
+    $budget = Budget::factory()->create([
+        'user_id' => $user->id,
+        'period_type' => BudgetPeriodType::Weekly,
+        'period_start_day' => 1,
+    ]);
+
+    BudgetPeriod::factory()->create([
+        'budget_id' => $budget->id,
+        'start_date' => '2026-05-04',
+        'end_date' => '2026-05-10',
+        'allocated_amount' => 10000,
+    ]);
+
+    $next = app(BudgetPeriodService::class)->generatePeriod($budget);
+
+    expect($next->start_date->toDateString())->toBe('2026-05-11');
+    expect($next->end_date->toDateString())->toBe('2026-05-17');
+});
+
+test('generatePeriod uses period_start_day snap when no prior periods exist', function () {
+    Carbon::setTestNow(Carbon::parse('2026-05-15 09:00:00'));
+
+    $user = User::factory()->create(['onboarded_at' => now()]);
+    $budget = Budget::factory()->create([
+        'user_id' => $user->id,
+        'period_type' => BudgetPeriodType::Monthly,
+        'period_start_day' => 1,
+    ]);
+
+    $period = app(BudgetPeriodService::class)->generatePeriod($budget);
+
+    expect($period->start_date->toDateString())->toBe('2026-05-01');
+    expect($period->end_date->toDateString())->toBe('2026-05-31');
+});