diff --git a/app/Http/Controllers/Api/V1/TimeEntryController.php b/app/Http/Controllers/Api/V1/TimeEntryController.php
index 62fee3fd..308c8577 100644
--- a/app/Http/Controllers/Api/V1/TimeEntryController.php
+++ b/app/Http/Controllers/Api/V1/TimeEntryController.php
@@ -13,9 +13,12 @@ use App\Http\Requests\V1\TimeEntry\TimeEntryUpdateMultipleRequest;
 use App\Http\Requests\V1\TimeEntry\TimeEntryUpdateRequest;
 use App\Http\Resources\V1\TimeEntry\TimeEntryCollection;
 use App\Http\Resources\V1\TimeEntry\TimeEntryResource;
+use App\Jobs\RecalculateSpentTimeForProject;
+use App\Jobs\RecalculateSpentTimeForTask;
 use App\Models\Member;
 use App\Models\Organization;
 use App\Models\Project;
+use App\Models\Task;
 use App\Models\TimeEntry;
 use App\Service\TimeEntryAggregationService;
 use App\Service\TimeEntryFilter;
@@ -215,7 +218,16 @@ class TimeEntryController extends Controller
             throw new TimeEntryStillRunningApiException;
         }
 
-        $client = $request->input('project_id') !== null ? Project::findOrFail((string) $request->input('project_id'))->client : null;
+        $project = $request->input('project_id') !== null ? Project::findOrFail((string) $request->input('project_id')) : null;
+        $client = $project?->client;
+        $task = $request->input('task_id') !== null ? $project->tasks()->findOrFail((string) $request->input('task_id')) : null;
+
+        if ($project !== null) {
+            RecalculateSpentTimeForProject::dispatch($project);
+        }
+        if ($task !== null) {
+            RecalculateSpentTimeForTask::dispatch($task);
+        }
 
         $timeEntry = new TimeEntry;
         $timeEntry->fill($request->validated());
@@ -250,16 +262,38 @@ class TimeEntryController extends Controller
             throw new TimeEntryCanNotBeRestartedApiException;
         }
 
+        $oldProject = $timeEntry->project;
+        $oldTask = $timeEntry->task;
+
+        $project = null;
         if ($request->has('project_id')) {
-            $client = $request->input('project_id') !== null ? Project::findOrFail((string) $request->input('project_id'))->client : null;
+            $project = $request->input('project_id') !== null ? Project::findOrFail((string) $request->input('project_id')) : null;
+            $client = $project?->client;
             $timeEntry->client()->associate($client);
         }
+        $task = null;
+        if ($request->has('task_id')) {
+            $task = $request->input('task_id') !== null ? Task::findOrFail((string) $request->input('task_id')) : null;
+        }
 
         $timeEntry->fill($request->validated());
         $timeEntry->description = $request->input('description', $timeEntry->description) ?? '';
         $timeEntry->setComputedAttributeValue('billable_rate');
         $timeEntry->save();
 
+        if ($oldProject !== null) {
+            RecalculateSpentTimeForProject::dispatch($oldProject);
+        }
+        if ($oldTask !== null) {
+            RecalculateSpentTimeForTask::dispatch($oldTask);
+        }
+        if ($project !== null && ($oldProject === null || $project->isNot($oldProject))) {
+            RecalculateSpentTimeForProject::dispatch($project);
+        }
+        if ($task !== null && ($oldTask === null || $task->isNot($oldTask))) {
+            RecalculateSpentTimeForTask::dispatch($task);
+        }
+
         return new TimeEntryResource($timeEntry);
     }
 
@@ -279,6 +313,10 @@ class TimeEntryController extends Controller
 
         $timeEntries = TimeEntry::query()
             ->whereBelongsTo($organization, 'organization')
+            ->with([
+                'project',
+                'task',
+            ])
             ->whereIn('id', $ids)
             ->get();
 
@@ -288,13 +326,20 @@ class TimeEntryController extends Controller
             throw new AuthorizationException;
         }
 
+        $project = null;
         $client = null;
         $overwriteClient = false;
         if ($request->has('changes.project_id')) {
-            $client = $request->input('changes.project_id') !== null ? Project::findOrFail((string) $request->input('changes.project_id'))->client : null;
+            $project = $request->input('changes.project_id') !== null ? Project::findOrFail((string) $request->input('changes.project_id')) : null;
+            $client = $project?->client;
             $overwriteClient = true;
         }
 
+        $task = null;
+        if ($request->has('changes.task_id')) {
+            $task = $request->input('changes.task_id') !== null ? Task::findOrFail((string) $request->input('changes.task_id')) : null;
+        }
+
         $success = new Collection;
         $error = new Collection;
 
@@ -313,12 +358,28 @@ class TimeEntryController extends Controller
                 continue;
 
             }
+            $oldProject = $timeEntry->project;
+            $oldTask = $timeEntry->task;
+
             $timeEntry->fill($changes);
             if ($overwriteClient) {
                 $timeEntry->client()->associate($client);
             }
             $timeEntry->setComputedAttributeValue('billable_rate');
             $timeEntry->save();
+            if ($oldTask !== null) {
+                RecalculateSpentTimeForTask::dispatch($oldTask);
+            }
+            if ($oldProject !== null) {
+                RecalculateSpentTimeForProject::dispatch($oldProject);
+            }
+            if ($project !== null && ($oldProject === null || $project->isNot($oldProject))) {
+                RecalculateSpentTimeForProject::dispatch($project);
+            }
+            if ($task !== null && ($oldTask === null || $task->isNot($oldTask))) {
+                RecalculateSpentTimeForTask::dispatch($task);
+            }
+
             $success->push($id);
         }
 
@@ -343,8 +404,18 @@ class TimeEntryController extends Controller
             $this->checkPermission($organization, 'time-entries:delete:all', $timeEntry);
         }
 
+        $project = $timeEntry->project;
+        $task = $timeEntry->task;
+
         $timeEntry->delete();
 
+        if ($project !== null) {
+            RecalculateSpentTimeForProject::dispatch($project);
+        }
+        if ($task !== null) {
+            RecalculateSpentTimeForTask::dispatch($task);
+        }
+
         return response()
             ->json(null, 204);
     }
diff --git a/app/Http/Resources/V1/Project/ProjectResource.php b/app/Http/Resources/V1/Project/ProjectResource.php
index 2d8567cd..e96f2f04 100644
--- a/app/Http/Resources/V1/Project/ProjectResource.php
+++ b/app/Http/Resources/V1/Project/ProjectResource.php
@@ -37,6 +37,8 @@ class ProjectResource extends BaseResource
             'is_billable' => $this->resource->is_billable,
             /** @var int|null $estimated_time Estimated time in seconds */
             'estimated_time' => $this->resource->estimated_time,
+            /** @var int $spent_time Spent time on this project in seconds (sum of the duration of all associated time entries, excl. still running time entries) */
+            'spent_time' => $this->resource->spent_time,
         ];
     }
 }
diff --git a/app/Http/Resources/V1/Task/TaskResource.php b/app/Http/Resources/V1/Task/TaskResource.php
index 26107935..67411b00 100644
--- a/app/Http/Resources/V1/Task/TaskResource.php
+++ b/app/Http/Resources/V1/Task/TaskResource.php
@@ -32,6 +32,8 @@ class TaskResource extends BaseResource
             'project_id' => $this->resource->project_id,
             /** @var int|null $estimated_time Estimated time in seconds */
             'estimated_time' => $this->resource->estimated_time,
+            /** @var int $spent_time Spent time on this task in seconds (sum of the duration of all associated time entries, excl. still running time entries) */
+            'spent_time' => $this->resource->spent_time,
             /** @var string $created_at When the tag was created */
             'created_at' => $this->formatDateTime($this->resource->created_at),
             /** @var string $updated_at When the tag was last updated */
diff --git a/app/Jobs/RecalculateSpentTimeForProject.php b/app/Jobs/RecalculateSpentTimeForProject.php
new file mode 100644
index 00000000..528ddcc3
--- /dev/null
+++ b/app/Jobs/RecalculateSpentTimeForProject.php
@@ -0,0 +1,44 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Jobs;
+
+use App\Models\Project;
+use Exception;
+use Illuminate\Bus\Queueable;
+use Illuminate\Contracts\Queue\ShouldQueue;
+use Illuminate\Foundation\Bus\Dispatchable;
+use Illuminate\Queue\InteractsWithQueue;
+use Illuminate\Queue\SerializesModels;
+
+class RecalculateSpentTimeForProject implements ShouldQueue
+{
+    use Dispatchable;
+    use InteractsWithQueue;
+    use Queueable;
+    use SerializesModels;
+
+    public Project $project;
+
+    /**
+     * Create a new job instance.
+     */
+    public function __construct(Project $project)
+    {
+        $this->project = $project;
+    }
+
+    /**
+     * Execute the job.
+     *
+     * @throws Exception
+     */
+    public function handle(): void
+    {
+        $this->project->setComputedAttributeValue('spent_time');
+        if ($this->project->isDirty()) {
+            $this->project->save();
+        }
+    }
+}
diff --git a/app/Jobs/RecalculateSpentTimeForTask.php b/app/Jobs/RecalculateSpentTimeForTask.php
new file mode 100644
index 00000000..fb5e38de
--- /dev/null
+++ b/app/Jobs/RecalculateSpentTimeForTask.php
@@ -0,0 +1,44 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Jobs;
+
+use App\Models\Task;
+use Exception;
+use Illuminate\Bus\Queueable;
+use Illuminate\Contracts\Queue\ShouldQueue;
+use Illuminate\Foundation\Bus\Dispatchable;
+use Illuminate\Queue\InteractsWithQueue;
+use Illuminate\Queue\SerializesModels;
+
+class RecalculateSpentTimeForTask implements ShouldQueue
+{
+    use Dispatchable;
+    use InteractsWithQueue;
+    use Queueable;
+    use SerializesModels;
+
+    public Task $task;
+
+    /**
+     * Create a new job instance.
+     */
+    public function __construct(Task $task)
+    {
+        $this->task = $task;
+    }
+
+    /**
+     * Execute the job.
+     *
+     * @throws Exception
+     */
+    public function handle(): void
+    {
+        $this->task->setComputedAttributeValue('spent_time');
+        if ($this->task->isDirty()) {
+            $this->task->save();
+        }
+    }
+}
diff --git a/app/Models/Project.php b/app/Models/Project.php
index 4eb555c7..7bf8ef02 100644
--- a/app/Models/Project.php
+++ b/app/Models/Project.php
@@ -15,6 +15,8 @@ use Illuminate\Database\Eloquent\Model;
 use Illuminate\Database\Eloquent\Relations\BelongsTo;
 use Illuminate\Database\Eloquent\Relations\HasMany;
 use Illuminate\Support\Carbon;
+use Illuminate\Support\Facades\DB;
+use Korridor\LaravelComputedAttributes\ComputedAttributes;
 use OwenIt\Auditing\Contracts\Auditable as AuditableContract;
 
 /**
@@ -28,6 +30,7 @@ use OwenIt\Auditing\Contracts\Auditable as AuditableContract;
  * @property bool $is_billable
  * @property-read bool $is_archived
  * @property int|null $estimated_time
+ * @property int $spent_time
  * @property Carbon|null $archived_at
  * @property Carbon|null $created_at
  * @property Carbon|null $updated_at
@@ -41,6 +44,7 @@ use OwenIt\Auditing\Contracts\Auditable as AuditableContract;
  */
 class Project extends Model implements AuditableContract
 {
+    use ComputedAttributes;
     use CustomAuditable;
 
     /** @use HasFactory<ProjectFactory> */
@@ -58,6 +62,7 @@ class Project extends Model implements AuditableContract
         'color' => 'string',
         'archived_at' => 'datetime',
         'estimated_time' => 'integer',
+        'spent_time' => 'integer',
     ];
 
     /**
@@ -69,6 +74,68 @@ class Project extends Model implements AuditableContract
         'is_billable' => false,
     ];
 
+    /**
+     * The attributes that are computed. (f.e. for performance reasons)
+     * These attributes can be regenerated at any time.
+     *
+     * @var string[]
+     */
+    protected array $computed = [
+        'spent_time',
+    ];
+
+    /**
+     * Attributes to exclude from the Audit.
+     *
+     * @var array<string>
+     */
+    protected array $auditExclude = [
+        'spent_time',
+    ];
+
+    public function getSpentTimeComputed(): ?int
+    {
+        if ($this->hasAttribute('spent_time_computed')) {
+            return $this->attributes['spent_time_computed'] === null ? 0 : (int) $this->attributes['spent_time_computed'];
+        } else {
+            /** @var object{ spent_time: string } $result */
+            $result = $this->timeEntries()
+                ->whereNotNull('end')
+                ->selectRaw('sum(extract(epoch from ("end" - start))) as spent_time')
+                ->first();
+
+            return (int) $result->spent_time;
+        }
+    }
+
+    /**
+     * This scope will be applied during the computed property generation with artisan computed-attributes:generate.
+     *
+     * @param  Builder<Project>  $builder
+     * @param  array<string>  $attributes  Attributes that will be generated.
+     * @return Builder<Project>
+     */
+    public function scopeComputedAttributesGenerate(Builder $builder, array $attributes): Builder
+    {
+        if (in_array('spent_time', $attributes, true)) {
+            $builder->withAggregate('timeEntries as spent_time_computed', DB::raw('extract(epoch from ("end" - start))'), 'sum');
+        }
+
+        return $builder;
+    }
+
+    /**
+     * This scope will be applied during the computed property validation with artisan computed-attributes:validate.
+     *
+     * @param  Builder<Project>  $builder
+     * @param  array<string>  $attributes  Attributes that will be validated.
+     * @return Builder<Project>
+     */
+    public function scopeComputedAttributesValidate(Builder $builder, array $attributes): Builder
+    {
+        return $this->scopeComputedAttributesGenerate($builder, $attributes);
+    }
+
     /**
      * @return BelongsTo<Organization, Project>
      */
diff --git a/app/Models/Task.php b/app/Models/Task.php
index fa696505..0344107b 100644
--- a/app/Models/Task.php
+++ b/app/Models/Task.php
@@ -15,6 +15,8 @@ use Illuminate\Database\Eloquent\Model;
 use Illuminate\Database\Eloquent\Relations\BelongsTo;
 use Illuminate\Database\Eloquent\Relations\HasMany;
 use Illuminate\Support\Carbon;
+use Illuminate\Support\Facades\DB;
+use Korridor\LaravelComputedAttributes\ComputedAttributes;
 use OwenIt\Auditing\Contracts\Auditable as AuditableContract;
 
 /**
@@ -24,6 +26,7 @@ use OwenIt\Auditing\Contracts\Auditable as AuditableContract;
  * @property string $organization_id
  * @property Carbon|null $done_at
  * @property int|null $estimated_time
+ * @property int $spent_time
  * @property Carbon|null $created_at
  * @property Carbon|null $updated_at
  * @property-read Project $project
@@ -35,6 +38,7 @@ use OwenIt\Auditing\Contracts\Auditable as AuditableContract;
  */
 class Task extends Model implements AuditableContract
 {
+    use ComputedAttributes;
     use CustomAuditable;
 
     /** @use HasFactory<TaskFactory> */
@@ -53,6 +57,68 @@ class Task extends Model implements AuditableContract
         'done_at' => 'datetime',
     ];
 
+    /**
+     * The attributes that are computed. (f.e. for performance reasons)
+     * These attributes can be regenerated at any time.
+     *
+     * @var string[]
+     */
+    protected array $computed = [
+        'spent_time',
+    ];
+
+    /**
+     * Attributes to exclude from the Audit.
+     *
+     * @var array<string>
+     */
+    protected array $auditExclude = [
+        'spent_time',
+    ];
+
+    public function getSpentTimeComputed(): ?int
+    {
+        if ($this->hasAttribute('spent_time_computed')) {
+            return $this->attributes['spent_time_computed'] === null ? 0 : (int) $this->attributes['spent_time_computed'];
+        } else {
+            /** @var object{ spent_time: string } $result */
+            $result = $this->timeEntries()
+                ->whereNotNull('end')
+                ->selectRaw('sum(extract(epoch from ("end" - start))) as spent_time')
+                ->first();
+
+            return (int) $result->spent_time;
+        }
+    }
+
+    /**
+     * This scope will be applied during the computed property generation with artisan computed-attributes:generate.
+     *
+     * @param  Builder<Task>  $builder
+     * @param  array<string>  $attributes  Attributes that will be generated.
+     * @return Builder<Task>
+     */
+    public function scopeComputedAttributesGenerate(Builder $builder, array $attributes): Builder
+    {
+        if (in_array('spent_time', $attributes, true)) {
+            $builder->withAggregate('timeEntries as spent_time_computed', DB::raw('extract(epoch from ("end" - start))'), 'sum');
+        }
+
+        return $builder;
+    }
+
+    /**
+     * This scope will be applied during the computed property validation with artisan computed-attributes:validate.
+     *
+     * @param  Builder<Task>  $builder
+     * @param  array<string>  $attributes  Attributes that will be validated.
+     * @return Builder<Task>
+     */
+    public function scopeComputedAttributesValidate(Builder $builder, array $attributes): Builder
+    {
+        return $this->scopeComputedAttributesGenerate($builder, $attributes);
+    }
+
     /**
      * @return BelongsTo<Project, Task>
      */
diff --git a/app/Models/TimeEntry.php b/app/Models/TimeEntry.php
index c2276e16..9412ab60 100644
--- a/app/Models/TimeEntry.php
+++ b/app/Models/TimeEntry.php
@@ -81,6 +81,15 @@ class TimeEntry extends Model implements AuditableContract
         'billable_rate',
     ];
 
+    /**
+     * Attributes to exclude from the Audit.
+     *
+     * @var array<string>
+     */
+    protected array $auditExclude = [
+        'billable_rate',
+    ];
+
     public function getBillableRateComputed(): ?int
     {
         return app(BillableRateService::class)->getBillableRateForTimeEntry($this);
diff --git a/database/migrations/2024_09_18_120203_add_spent_time_to_projects_and_tasks_table.php b/database/migrations/2024_09_18_120203_add_spent_time_to_projects_and_tasks_table.php
new file mode 100644
index 00000000..7dd7eed0
--- /dev/null
+++ b/database/migrations/2024_09_18_120203_add_spent_time_to_projects_and_tasks_table.php
@@ -0,0 +1,36 @@
+<?php
+
+declare(strict_types=1);
+
+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('projects', function (Blueprint $table): void {
+            $table->integer('spent_time')->unsigned()->default(0);
+        });
+        Schema::table('tasks', function (Blueprint $table): void {
+            $table->integer('spent_time')->unsigned()->default(0);
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::table('projects', function (Blueprint $table): void {
+            $table->dropColumn('spent_time');
+        });
+        Schema::table('tasks', function (Blueprint $table): void {
+            $table->dropColumn('spent_time');
+        });
+    }
+};
diff --git a/tests/Unit/Endpoint/Api/V1/TimeEntryEndpointTest.php b/tests/Unit/Endpoint/Api/V1/TimeEntryEndpointTest.php
index c715e358..23a6d958 100644
--- a/tests/Unit/Endpoint/Api/V1/TimeEntryEndpointTest.php
+++ b/tests/Unit/Endpoint/Api/V1/TimeEntryEndpointTest.php
@@ -7,6 +7,8 @@ namespace Tests\Unit\Endpoint\Api\V1;
 use App\Enums\Role;
 use App\Exceptions\Api\TimeEntryCanNotBeRestartedApiException;
 use App\Http\Controllers\Api\V1\TimeEntryController;
+use App\Jobs\RecalculateSpentTimeForProject;
+use App\Jobs\RecalculateSpentTimeForTask;
 use App\Models\Client;
 use App\Models\Member;
 use App\Models\Project;
@@ -16,6 +18,7 @@ use App\Models\TimeEntry;
 use App\Models\User;
 use Illuminate\Support\Carbon;
 use Illuminate\Support\Facades\Log;
+use Illuminate\Support\Facades\Queue;
 use Illuminate\Support\Str;
 use Illuminate\Testing\Fluent\AssertableJson;
 use Laravel\Passport\Passport;
@@ -1050,6 +1053,45 @@ class TimeEntryEndpointTest extends ApiEndpointTestAbstract
         ]);
     }
 
+    public function test_create_endpoint_recalculates_project_and_task_spent_time_if_time_entry_has_project_and_task(): void
+    {
+        // Arrange
+        $data = $this->createUserWithPermission([
+            'time-entries:create:own',
+        ]);
+        $project = Project::factory()->forOrganization($data->organization)->create();
+        $task = Task::factory()->forOrganization($data->organization)->forProject($project)->create();
+        TimeEntry::factory()->forOrganization($data->organization)->forMember($data->member)->forProject($project)->forTask($task)->create();
+        $timeEntryFake = TimeEntry::factory()->forOrganization($data->organization)->make();
+        Passport::actingAs($data->user);
+        Queue::fake([
+            RecalculateSpentTimeForProject::class,
+            RecalculateSpentTimeForTask::class,
+        ]);
+
+        // Act
+        $response = $this->postJson(route('api.v1.time-entries.store', [$data->organization->getKey()]), [
+            'description' => $timeEntryFake->description,
+            'billable' => $timeEntryFake->billable,
+            'start' => Carbon::now()->toIso8601ZuluString(),
+            'end' => Carbon::now()->addHour()->toIso8601ZuluString(),
+            'member_id' => $data->member->getKey(),
+            'project_id' => $project->getKey(),
+            'task_id' => $task->getKey(),
+        ]);
+
+        // Assert
+        $response->assertStatus(201);
+        Queue::assertPushed(RecalculateSpentTimeForProject::class, 1);
+        Queue::assertPushed(RecalculateSpentTimeForTask::class, 1);
+        Queue::assertPushed(RecalculateSpentTimeForProject::class, function (RecalculateSpentTimeForProject $job) use ($project): bool {
+            return $job->project->is($project);
+        });
+        Queue::assertPushed(RecalculateSpentTimeForTask::class, function (RecalculateSpentTimeForTask $job) use ($task): bool {
+            return $job->task->is($task);
+        });
+    }
+
     public function test_update_endpoint_fails_if_user_has_no_permission_to_update_own_time_entries(): void
     {
         // Arrange
@@ -1385,6 +1427,82 @@ class TimeEntryEndpointTest extends ApiEndpointTestAbstract
         ]);
     }
 
+    public function test_update_endpoint_recalculates_project_and_task_spend_time_after_updating_time_entry_settings_a_project_and_a_task(): void
+    {
+        // Arrange
+        $data = $this->createUserWithPermission([
+            'time-entries:update:own',
+        ]);
+        $project = Project::factory()->forOrganization($data->organization)->create();
+        $task = Task::factory()->forOrganization($data->organization)->forProject($project)->create();
+        $timeEntry = TimeEntry::factory()->forOrganization($data->organization)->forProject(null)->forTask(null)->forMember($data->member)->create();
+        TimeEntry::factory()->forOrganization($data->organization)->make();
+        Passport::actingAs($data->user);
+        Queue::fake([
+            RecalculateSpentTimeForProject::class,
+            RecalculateSpentTimeForTask::class,
+        ]);
+
+        // Act
+        $response = $this->putJson(route('api.v1.time-entries.update', [$data->organization->getKey(), $timeEntry->getKey()]), [
+            'project_id' => $project->getKey(),
+            'task_id' => $task->getKey(),
+        ]);
+
+        // Assert
+        $response->assertStatus(200);
+        Queue::assertPushed(RecalculateSpentTimeForProject::class, 1);
+        Queue::assertPushed(RecalculateSpentTimeForTask::class, 1);
+        Queue::assertPushed(function (RecalculateSpentTimeForProject $job) use ($project): bool {
+            return $job->project->is($project);
+        }, 1);
+        Queue::assertPushed(function (RecalculateSpentTimeForTask $job) use ($task): bool {
+            return $job->task->is($task);
+        }, 1);
+    }
+
+    public function test_update_endpoint_recalculates_project_and_task_spend_time_after_updating_time_entry_settings_a_new_project_and_a_new_task(): void
+    {
+        // Arrange
+        $data = $this->createUserWithPermission([
+            'time-entries:update:own',
+        ]);
+        $oldProject = Project::factory()->forOrganization($data->organization)->create();
+        $oldTask = Task::factory()->forOrganization($data->organization)->forProject($oldProject)->create();
+        $timeEntry = TimeEntry::factory()->forOrganization($data->organization)->forProject($oldProject)->forTask($oldTask)->forMember($data->member)->create();
+        $project = Project::factory()->forOrganization($data->organization)->create();
+        $task = Task::factory()->forOrganization($data->organization)->forProject($project)->create();
+        TimeEntry::factory()->forOrganization($data->organization)->make();
+        Passport::actingAs($data->user);
+        Queue::fake([
+            RecalculateSpentTimeForProject::class,
+            RecalculateSpentTimeForTask::class,
+        ]);
+
+        // Act
+        $response = $this->putJson(route('api.v1.time-entries.update', [$data->organization->getKey(), $timeEntry->getKey()]), [
+            'project_id' => $project->getKey(),
+            'task_id' => $task->getKey(),
+        ]);
+
+        // Assert
+        $response->assertStatus(200);
+        Queue::assertPushed(RecalculateSpentTimeForProject::class, 2);
+        Queue::assertPushed(RecalculateSpentTimeForTask::class, 2);
+        Queue::assertPushed(function (RecalculateSpentTimeForProject $job) use ($project): bool {
+            return $job->project->is($project);
+        }, 1);
+        Queue::assertPushed(function (RecalculateSpentTimeForProject $job) use ($oldProject): bool {
+            return $job->project->is($oldProject);
+        }, 1);
+        Queue::assertPushed(function (RecalculateSpentTimeForTask $job) use ($task): bool {
+            return $job->task->is($task);
+        }, 1);
+        Queue::assertPushed(function (RecalculateSpentTimeForTask $job) use ($oldTask): bool {
+            return $job->task->is($oldTask);
+        }, 1);
+    }
+
     public function test_destroy_endpoint_fails_if_user_tries_to_delete_time_entry_in_organization_that_they_does_belong_to(): void
     {
         // Arrange
@@ -1493,6 +1611,68 @@ class TimeEntryEndpointTest extends ApiEndpointTestAbstract
         ]);
     }
 
+    public function test_destroy_endpoint_recalculates_project_and_task_spend_time_after_deleting_time_entry(): void
+    {
+        // Arrange
+        $data = $this->createUserWithPermission([
+            'time-entries:delete:own',
+        ]);
+        $project = Project::factory()->forOrganization($data->organization)->create();
+        $task = Task::factory()->forOrganization($data->organization)->create();
+        $timeEntry = TimeEntry::factory()->forOrganization($data->organization)->forProject($project)->forTask($task)->forMember($data->member)->create();
+        $project = $timeEntry->project;
+        $task = $timeEntry->task;
+        Passport::actingAs($data->user);
+        Queue::fake([
+            RecalculateSpentTimeForProject::class,
+            RecalculateSpentTimeForTask::class,
+        ]);
+
+        // Act
+        $response = $this->deleteJson(route('api.v1.time-entries.destroy', [$data->organization->getKey(), $timeEntry->getKey()]));
+
+        // Assert
+        $response->assertStatus(204);
+        $response->assertNoContent();
+        $this->assertDatabaseMissing(TimeEntry::class, [
+            'id' => $timeEntry->getKey(),
+        ]);
+        Queue::assertPushed(RecalculateSpentTimeForProject::class, 1);
+        Queue::assertPushed(RecalculateSpentTimeForTask::class, 1);
+        Queue::assertPushed(RecalculateSpentTimeForProject::class, function (RecalculateSpentTimeForProject $job) use ($project) {
+            return $job->project->is($project);
+        });
+        Queue::assertPushed(RecalculateSpentTimeForTask::class, function (RecalculateSpentTimeForTask $job) use ($task) {
+            return $job->task->is($task);
+        });
+    }
+
+    public function test_destroy_endpoint_does_not_recalculate_project_and_task_spend_time_after_deleting_time_entry_if_time_entry_had_no_project_and_task(): void
+    {
+        // Arrange
+        $data = $this->createUserWithPermission([
+            'time-entries:delete:own',
+        ]);
+        $timeEntry = TimeEntry::factory()->forOrganization($data->organization)->forProject(null)->forTask(null)->forMember($data->member)->create();
+        Passport::actingAs($data->user);
+        Queue::fake([
+            RecalculateSpentTimeForProject::class,
+            RecalculateSpentTimeForTask::class,
+        ]);
+
+        // Act
+        $response = $this->deleteJson(route('api.v1.time-entries.destroy', [$data->organization->getKey(), $timeEntry->getKey()]));
+
+        // Assert
+        $response->assertStatus(204);
+        $response->assertNoContent();
+        $this->assertDatabaseMissing(TimeEntry::class, [
+            'id' => $timeEntry->getKey(),
+        ]);
+        Queue::assertNotPushed(RecalculateSpentTimeForProject::class);
+        Queue::assertNotPushed(RecalculateSpentTimeForTask::class);
+    }
+
     public function test_update_multiple_endpoint_fails_if_user_has_no_permission_to_update_own_time_entries_or_all_time_entries(): void
     {
         // Arrange
diff --git a/tests/Unit/Jobs/RecalculateSpentTimeForProjectTest.php b/tests/Unit/Jobs/RecalculateSpentTimeForProjectTest.php
new file mode 100644
index 00000000..ec982f49
--- /dev/null
+++ b/tests/Unit/Jobs/RecalculateSpentTimeForProjectTest.php
@@ -0,0 +1,58 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\Unit\Jobs;
+
+use App\Jobs\RecalculateSpentTimeForProject;
+use App\Models\Project;
+use App\Models\TimeEntry;
+use Illuminate\Support\Facades\DB;
+use Tests\TestCaseWithDatabase;
+
+class RecalculateSpentTimeForProjectTest extends TestCaseWithDatabase
+{
+    public function test_recalculates_spent_time_for_project(): void
+    {
+        // Arrange
+        $project = Project::factory()->create([
+            'spent_time' => 0,
+        ]);
+        TimeEntry::factory()->startWithDuration(now(), 10)->forProject($project)->create();
+        TimeEntry::factory()->startWithDuration(now(), 11)->forProject($project)->create();
+
+        $project->refresh();
+        $recalculateSpentTimeForProject = new RecalculateSpentTimeForProject($project);
+        DB::enableQueryLog();
+
+        // Act
+        $recalculateSpentTimeForProject->handle();
+
+        // Assert
+        self::assertCount(2, DB::getQueryLog());
+        $project->refresh();
+        self::assertEquals(21, $project->spent_time);
+    }
+
+    public function test_does_not_save_project_if_value_is_already_correct(): void
+    {
+        // Arrange
+        $project = Project::factory()->create([
+            'spent_time' => 21,
+        ]);
+        TimeEntry::factory()->startWithDuration(now(), 10)->forProject($project)->create();
+        TimeEntry::factory()->startWithDuration(now(), 11)->forProject($project)->create();
+
+        $project->refresh();
+        $recalculateSpentTimeForProject = new RecalculateSpentTimeForProject($project);
+        DB::enableQueryLog();
+
+        // Act
+        $recalculateSpentTimeForProject->handle();
+
+        // Assert
+        self::assertCount(1, DB::getQueryLog());
+        $project->refresh();
+        self::assertEquals(21, $project->spent_time);
+    }
+}
diff --git a/tests/Unit/Jobs/RecalculateSpentTimeForTaskTest.php b/tests/Unit/Jobs/RecalculateSpentTimeForTaskTest.php
new file mode 100644
index 00000000..6aed29b1
--- /dev/null
+++ b/tests/Unit/Jobs/RecalculateSpentTimeForTaskTest.php
@@ -0,0 +1,58 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\Unit\Jobs;
+
+use App\Jobs\RecalculateSpentTimeForTask;
+use App\Models\Task;
+use App\Models\TimeEntry;
+use Illuminate\Support\Facades\DB;
+use Tests\TestCaseWithDatabase;
+
+class RecalculateSpentTimeForTaskTest extends TestCaseWithDatabase
+{
+    public function test_recalculates_spent_time_for_task(): void
+    {
+        // Arrange
+        $task = Task::factory()->create([
+            'spent_time' => 0,
+        ]);
+        TimeEntry::factory()->startWithDuration(now(), 10)->forTask($task)->create();
+        TimeEntry::factory()->startWithDuration(now(), 11)->forTask($task)->create();
+
+        $task->refresh();
+        $recalculateSpentTimeForTask = new RecalculateSpentTimeForTask($task);
+        DB::enableQueryLog();
+
+        // Act
+        $recalculateSpentTimeForTask->handle();
+
+        // Assert
+        self::assertCount(2, DB::getQueryLog());
+        $task->refresh();
+        self::assertEquals(21, $task->spent_time);
+    }
+
+    public function test_does_not_save_task_if_value_is_already_correct(): void
+    {
+        // Arrange
+        $task = Task::factory()->create([
+            'spent_time' => 21,
+        ]);
+        TimeEntry::factory()->startWithDuration(now(), 10)->forTask($task)->create();
+        TimeEntry::factory()->startWithDuration(now(), 11)->forTask($task)->create();
+
+        $task->refresh();
+        $recalculateSpentTimeForTask = new RecalculateSpentTimeForTask($task);
+        DB::enableQueryLog();
+
+        // Act
+        $recalculateSpentTimeForTask->handle();
+
+        // Assert
+        self::assertCount(1, DB::getQueryLog());
+        $task->refresh();
+        self::assertEquals(21, $task->spent_time);
+    }
+}
diff --git a/tests/Unit/Jobs/Test/TestJobTest.php b/tests/Unit/Jobs/Test/TestJobTest.php
new file mode 100644
index 00000000..b65440ad
--- /dev/null
+++ b/tests/Unit/Jobs/Test/TestJobTest.php
@@ -0,0 +1,51 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\Unit\Jobs\Test;
+
+use App\Jobs\Test\TestJob;
+use App\Models\User;
+use Illuminate\Support\Facades\Log;
+use Tests\TestCaseWithDatabase;
+use TiMacDonald\Log\LogEntry;
+
+class TestJobTest extends TestCaseWithDatabase
+{
+    public function test_logs_debug_message(): void
+    {
+        // Arrange
+        $user = User::factory()->create();
+        $message = 'Test message';
+        $job = new TestJob($user, $message);
+
+        // Act
+        $job->handle();
+
+        // Assert
+        Log::assertLoggedTimes(fn (LogEntry $log) => $log->level === 'debug'
+            && $log->message === 'TestJob: '.$message
+            && $log->context['user'] === $user->getKey(),
+            1
+        );
+    }
+
+    public function test_can_fail_if_parameter_fail_is_true(): void
+    {
+        // Arrange
+        $user = User::factory()->create();
+        $message = 'Test message';
+        $job = new TestJob($user, $message, true);
+
+        // Act
+        try {
+            $job->handle();
+        } catch (\Exception $e) {
+            // Assert
+            $this->assertEquals('TestJob failed.', $e->getMessage());
+
+            return;
+        }
+        $this->fail('Expected exception not thrown');
+    }
+}
diff --git a/tests/Unit/Model/ProjectModelTest.php b/tests/Unit/Model/ProjectModelTest.php
index 5bda407d..c9056514 100644
--- a/tests/Unit/Model/ProjectModelTest.php
+++ b/tests/Unit/Model/ProjectModelTest.php
@@ -10,6 +10,8 @@ use App\Models\Organization;
 use App\Models\Project;
 use App\Models\ProjectMember;
 use App\Models\Task;
+use App\Models\TimeEntry;
+use Illuminate\Support\Facades\DB;
 use PHPUnit\Framework\Attributes\CoversClass;
 use PHPUnit\Framework\Attributes\UsesClass;
 
@@ -117,6 +119,47 @@ class ProjectModelTest extends ModelTestAbstract
         ], $allProjects);
     }
 
+    public function test_computed_spent_time_returns_the_sum_of_all_time_entries_excl_running_timers(): void
+    {
+        // Arrange
+        $project = Project::factory()->create();
+        $otherProject = Project::factory()->create();
+        TimeEntry::factory()->forProject($project)->startWithDuration(now(), 10)->create();
+        TimeEntry::factory()->forProject($project)->startWithDuration(now(), 10)->create();
+        TimeEntry::factory()->forProject($project)->startWithDuration(now(), 10)->create();
+        TimeEntry::factory()->forProject($otherProject)->startWithDuration(now(), 10)->create();
+        TimeEntry::factory()->forProject($otherProject)->start(now())->active()->create();
+
+        // Act
+        $project->refresh();
+        $spentTime = $project->getSpentTimeComputed();
+
+        // Assert
+        $this->assertEquals(30, $spentTime);
+    }
+
+    public function test_computed_spent_time_returns_already_computed_value_if_present(): void
+    {
+        // Arrange
+        $project = Project::factory()->create();
+        $otherProject = Project::factory()->create();
+        TimeEntry::factory()->forProject($project)->startWithDuration(now(), 10)->create();
+        TimeEntry::factory()->forProject($project)->startWithDuration(now(), 10)->create();
+        TimeEntry::factory()->forProject($project)->startWithDuration(now(), 10)->create();
+        TimeEntry::factory()->forProject($otherProject)->startWithDuration(now(), 10)->create();
+        TimeEntry::factory()->forProject($otherProject)->start(now())->active()->create();
+        $timeEntries = Project::query()
+            ->withAggregate('timeEntries as spent_time_computed', DB::raw('extract(epoch from ("end" - start))'), 'sum')
+            ->get();
+
+        // Act
+        $project->refresh();
+        $spentTime = $timeEntries->first()->getSpentTimeComputed();
+
+        // Assert
+        $this->assertEquals(30, $spentTime);
+    }
+
     public function test_accessor_is_archived_is_true_if_archived_at_is_not_null(): void
     {
         // Arrange