diff --git a/app/Services/BudgetPeriodService.php b/app/Services/BudgetPeriodService.php
index 38c283fb..7e105c43 100644
--- a/app/Services/BudgetPeriodService.php
+++ b/app/Services/BudgetPeriodService.php
@@ -17,20 +17,30 @@ class BudgetPeriodService
 
         [$periodStart, $periodEnd] = $this->calculatePeriodDates($budget, $startDate);
 
+        $periodStart = $periodStart->startOfDay();
+        $periodEnd = $periodEnd->startOfDay();
+
         // If no allocated amount provided, use the last period's amount or 0
         if ($allocatedAmount === null) {
             $lastPeriod = $budget->periods()->orderBy('end_date', 'desc')->first();
             $allocatedAmount = $lastPeriod !== null ? $lastPeriod->allocated_amount : 0;
         }
 
-        return BudgetPeriod::create([
-            'budget_id' => $budget->id,
-            'start_date' => $periodStart,
-            'end_date' => $periodEnd,
-            'allocated_amount' => $allocatedAmount,
-            'carried_over_amount' => 0,
-            'processing_historical' => $processHistorical,
-        ]);
+        // Idempotent on the (budget_id, start_date) unique key: the scheduled
+        // command can recompute the same next start date across overlapping or
+        // repeated runs, so return the existing period instead of colliding.
+        return BudgetPeriod::firstOrCreate(
+            [
+                'budget_id' => $budget->id,
+                'start_date' => $periodStart,
+            ],
+            [
+                'end_date' => $periodEnd,
+                'allocated_amount' => $allocatedAmount,
+                'carried_over_amount' => 0,
+                'processing_historical' => $processHistorical,
+            ],
+        );
     }
 
     public function generatePreviousPeriod(Budget $budget, BudgetPeriod $period, ?int $allocatedAmount = null, bool $processHistorical = false): BudgetPeriod
diff --git a/tests/Feature/BudgetPeriodServiceTest.php b/tests/Feature/BudgetPeriodServiceTest.php
index 7435507f..39bec78b 100644
--- a/tests/Feature/BudgetPeriodServiceTest.php
+++ b/tests/Feature/BudgetPeriodServiceTest.php
@@ -96,6 +96,30 @@ test('generatePeriod uses period_start_day snap when no prior periods exist', fu
     expect($period->end_date->toDateString())->toBe('2026-05-31');
 });
 
+test('generatePeriod is idempotent when a period already exists for the start date', function () {
+    Carbon::setTestNow(Carbon::parse('2026-06-15 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,
+    ]);
+
+    $existing = BudgetPeriod::factory()->create([
+        'budget_id' => $budget->id,
+        'start_date' => '2026-06-01',
+        'end_date' => '2026-06-30',
+        'allocated_amount' => 44500,
+    ]);
+
+    $period = app(BudgetPeriodService::class)->generatePeriod($budget, 100, Carbon::parse('2026-06-15'));
+
+    expect($period->id)->toBe($existing->id);
+    expect($period->allocated_amount)->toBe(44500);
+    expect(BudgetPeriod::where('budget_id', $budget->id)->count())->toBe(1);
+});
+
 test('generatePeriod creates current calendar year when yearly budget has no prior periods', function () {
     Carbon::setTestNow(Carbon::parse('2026-05-15 09:00:00'));