diff --git a/app/Http/Controllers/Api/DeliveryController.php b/app/Http/Controllers/Api/DeliveryController.php
index dd454c3..11acee7 100644
--- a/app/Http/Controllers/Api/DeliveryController.php
+++ b/app/Http/Controllers/Api/DeliveryController.php
@@ -6,6 +6,7 @@
 use App\Models\Delivery;
 use Illuminate\Http\JsonResponse;
 use Illuminate\Http\Request;
+use Illuminate\Support\Carbon;
 use Illuminate\Support\Facades\Validator;
 use Illuminate\Validation\Rule;
 
@@ -52,13 +53,15 @@ public function index(Request $request): JsonResponse
             $query->where('event_id', $request->input('event_id'));
         }
 
-        // Filter by date range
+        // Filter by date range. Comparing against a plain timestamp range
+        // (rather than wrapping created_at in whereDate()) keeps the query
+        // sargable so it can use the index on created_at.
         if ($request->has('from_date')) {
-            $query->whereDate('created_at', '>=', $request->input('from_date'));
+            $query->where('created_at', '>=', Carbon::parse($request->input('from_date'))->startOfDay());
         }
 
         if ($request->has('to_date')) {
-            $query->whereDate('created_at', '<=', $request->input('to_date'));
+            $query->where('created_at', '<', Carbon::parse($request->input('to_date'))->addDay()->startOfDay());
         }
 
         $deliveries = $query->orderBy('created_at', 'desc')
diff --git a/app/Http/Controllers/DashboardController.php b/app/Http/Controllers/DashboardController.php
index 05c8277..5f1f3fc 100644
--- a/app/Http/Controllers/DashboardController.php
+++ b/app/Http/Controllers/DashboardController.php
@@ -5,6 +5,7 @@
 use App\Models\Delivery;
 use App\Models\Event;
 use Illuminate\Http\Request;
+use Illuminate\Support\Carbon;
 use Inertia\Inertia;
 use Inertia\Response;
 
@@ -133,12 +134,15 @@ public function deliveries(Request $request): Response
             $query->whereHas('event', fn ($q) => $q->where('name', 'like', '%'.$request->event_name.'%'));
         }
 
+        // Comparing against a plain timestamp range (rather than wrapping
+        // created_at in whereDate()) keeps the query sargable so it can use
+        // the index on created_at.
         if ($request->has('from_date') && $request->from_date) {
-            $query->whereDate('created_at', '>=', $request->from_date);
+            $query->where('created_at', '>=', Carbon::parse($request->from_date)->startOfDay());
         }
 
         if ($request->has('to_date') && $request->to_date) {
-            $query->whereDate('created_at', '<=', $request->to_date);
+            $query->where('created_at', '<', Carbon::parse($request->to_date)->addDay()->startOfDay());
         }
 
         $statusCounts = (clone $query)
diff --git a/database/migrations/2026_09_21_000000_add_created_at_index_to_deliveries_table.php b/database/migrations/2026_09_21_000000_add_created_at_index_to_deliveries_table.php
new file mode 100644
index 0000000..ba6913e
--- /dev/null
+++ b/database/migrations/2026_09_21_000000_add_created_at_index_to_deliveries_table.php
@@ -0,0 +1,27 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class () extends Migration {
+    /**
+     * Run the migrations.
+     */
+    public function up(): void
+    {
+        Schema::table('deliveries', function (Blueprint $table) {
+            $table->index('created_at');
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::table('deliveries', function (Blueprint $table) {
+            $table->dropIndex(['created_at']);
+        });
+    }
+};
diff --git a/tests/Feature/DeliveryDateRangeFilterBoundaryTest.php b/tests/Feature/DeliveryDateRangeFilterBoundaryTest.php
new file mode 100644
index 0000000..df8883c
--- /dev/null
+++ b/tests/Feature/DeliveryDateRangeFilterBoundaryTest.php
@@ -0,0 +1,93 @@
+<?php
+
+namespace Tests\Feature;
+
+use App\Models\Delivery;
+use App\Models\Endpoint;
+use App\Models\Event;
+use App\Models\User;
+use Illuminate\Foundation\Testing\RefreshDatabase;
+use Illuminate\Support\Facades\Schema;
+use Tests\TestCase;
+
+class DeliveryDateRangeFilterBoundaryTest extends TestCase
+{
+    use RefreshDatabase;
+
+    public function test_deliveries_table_has_an_index_on_created_at(): void
+    {
+        $indexedColumns = collect(Schema::getIndexes('deliveries'))
+            ->pluck('columns')
+            ->flatten()
+            ->all();
+
+        $this->assertContains('created_at', $indexedColumns);
+    }
+
+    public function test_api_date_range_filter_includes_the_full_first_and_last_day(): void
+    {
+        $user = User::factory()->withPersonalTeam()->create();
+        $endpoint = Endpoint::factory()->for($user)->create();
+        $event = Event::factory()->for($user)->create();
+
+        $startOfFirstDay = Delivery::factory()->for($event)->for($endpoint)->create([
+            'created_at' => '2026-06-01 00:00:00',
+        ]);
+        $endOfLastDay = Delivery::factory()->for($event)->for($endpoint)->create([
+            'created_at' => '2026-06-30 23:59:59',
+        ]);
+        $beforeRange = Delivery::factory()->for($event)->for($endpoint)->create([
+            'created_at' => '2026-05-31 23:59:59',
+        ]);
+        $afterRange = Delivery::factory()->for($event)->for($endpoint)->create([
+            'created_at' => '2026-07-01 00:00:00',
+        ]);
+
+        $response = $this->actingAs($user)->getJson(
+            '/api/v1/deliveries?from_date=2026-06-01&to_date=2026-06-30'
+        );
+
+        $response->assertOk();
+        $ids = collect($response->json('data'))->pluck('id');
+
+        $this->assertTrue($ids->contains($startOfFirstDay->id));
+        $this->assertTrue($ids->contains($endOfLastDay->id));
+        $this->assertFalse($ids->contains($beforeRange->id));
+        $this->assertFalse($ids->contains($afterRange->id));
+    }
+
+    public function test_dashboard_date_range_filter_includes_the_full_first_and_last_day(): void
+    {
+        $user = User::factory()->withPersonalTeam()->create();
+        $endpoint = Endpoint::factory()->for($user)->create();
+        $event = Event::factory()->for($user)->create();
+
+        $startOfFirstDay = Delivery::factory()->for($event)->for($endpoint)->create([
+            'created_at' => '2026-06-01 00:00:00',
+        ]);
+        $endOfLastDay = Delivery::factory()->for($event)->for($endpoint)->create([
+            'created_at' => '2026-06-30 23:59:59',
+        ]);
+        $beforeRange = Delivery::factory()->for($event)->for($endpoint)->create([
+            'created_at' => '2026-05-31 23:59:59',
+        ]);
+        $afterRange = Delivery::factory()->for($event)->for($endpoint)->create([
+            'created_at' => '2026-07-01 00:00:00',
+        ]);
+
+        $response = $this->actingAs($user)->get(route('deliveries', [
+            'from_date' => '2026-06-01',
+            'to_date' => '2026-06-30',
+        ]));
+
+        $response->assertOk();
+        $response->assertInertia(
+            fn ($page) => $page
+                ->component('Deliveries/Index')
+                ->has('deliveries.data', 2)
+                // Ordered by latest() first, so the end-of-range delivery sorts before the start-of-range one.
+                ->where('deliveries.data.0.id', $endOfLastDay->id)
+                ->where('deliveries.data.1.id', $startOfFirstDay->id)
+        );
+    }
+}