diff --git a/src/bot/commands/task.ts b/src/bot/commands/task.ts
index 630684b..f58dddf 100644
--- a/src/bot/commands/task.ts
+++ b/src/bot/commands/task.ts
@@ -107,12 +107,19 @@ export function handleTaskCommand(body: string, sender: string, groupId: string,
             return;
           }
           
-          completeTask(taskId);
+          const completedTask = completeTask(taskId, sender);
           // Send confirmation privately to the user who completed
-          sendMessage(sender, `✅ Tarea ${taskId} completada: ${task.description}`);
+          sendMessage(sender, `✅ Tarea completada:\n` +
+            `ID: ${completedTask.id}\n` +
+            `Descripción: ${completedTask.description}\n` +
+            `Completada el: ${completedTask.completedAt}`);
+          
           // Notify the task creator if different from completer
-          if (task.createdBy && task.createdBy !== sender) {
-            sendMessage(task.createdBy, `✅ Tarea ${taskId} completada por @${sender.split('@')[0]}: ${task.description}`);
+          if (completedTask.createdBy && completedTask.createdBy !== sender) {
+            sendMessage(completedTask.createdBy, `✅ Tarea completada por @${sender.split('@')[0]}:\n` +
+              `ID: ${completedTask.id}\n` +
+              `Descripción: ${completedTask.description}\n` +
+              `Completada el: ${completedTask.completedAt}`);
           }
         } catch (error) {
           console.error('Error completing task:', error);
diff --git a/src/services/taskService.ts b/src/services/taskService.ts
index 6130392..4450e5f 100644
--- a/src/services/taskService.ts
+++ b/src/services/taskService.ts
@@ -43,11 +43,29 @@ export function assignTask(taskId: number, assignedTo: string) {
 }
 
 // Mark a task as completed
-export function completeTask(taskId: number) {
-  execute(
-    'UPDATE tasks SET completed = TRUE WHERE id = ?',
+export function completeTask(taskId: number, completedBy: string) {
+  const task = getTaskById(taskId);
+  if (!task) {
+    throw new Error('Tarea no encontrada');
+  }
+
+  // Only allow completion if task is assigned to the user or to no one
+  const currentUser = normalizeUserIdentifier(completedBy);
+  if (task.assignedTo && task.assignedTo !== currentUser) {
+    throw new Error('No puedes completar una tarea asignada a otro usuario');
+  }
+
+  const result = execute(
+    'UPDATE tasks SET completed = TRUE, completed_at = CURRENT_TIMESTAMP WHERE id = ?',
     [taskId]
   );
+
+  if (result.changes === 0) {
+    throw new Error('No se pudo completar la tarea');
+  }
+
+  // Return updated task with completion info
+  return getTaskById(taskId);
 }
 
 // Get all tasks (for debugging or future use)