diff --git a/core/db.py b/core/db.py
index dfc7047..bf1d10c 100644
--- a/core/db.py
+++ b/core/db.py
@@ -773,6 +773,12 @@ def _migrate(conn: sqlite3.Connection):
                 PRAGMA foreign_keys=ON;
             """)
 
+    # KIN-126: Add completed_at to tasks — set when task transitions to 'done'
+    task_cols_final = {r[1] for r in conn.execute("PRAGMA table_info(tasks)").fetchall()}
+    if "completed_at" not in task_cols_final:
+        conn.execute("ALTER TABLE tasks ADD COLUMN completed_at DATETIME DEFAULT NULL")
+        conn.commit()
+
 
 def _seed_default_hooks(conn: sqlite3.Connection):
     """Seed default hooks for the kin project (idempotent).
diff --git a/core/models.py b/core/models.py
index dde8f65..6d004f3 100644
--- a/core/models.py
+++ b/core/models.py
@@ -304,13 +304,15 @@ def list_tasks(
 
 
 def update_task(conn: sqlite3.Connection, id: str, **fields) -> dict:
-    """Update task fields. Auto-sets updated_at."""
+    """Update task fields. Auto-sets updated_at. Sets completed_at when status transitions to 'done'."""
     if not fields:
         return get_task(conn, id)
     json_cols = ("brief", "spec", "review", "test_result", "security_result", "labels")
     for key in json_cols:
         if key in fields:
             fields[key] = _json_encode(fields[key])
+    if "status" in fields and fields["status"] == "done":
+        fields["completed_at"] = datetime.now().isoformat()
     fields["updated_at"] = datetime.now().isoformat()
     sets = ", ".join(f"{k} = ?" for k in fields)
     vals = list(fields.values()) + [id]
diff --git a/web/frontend/src/api.ts b/web/frontend/src/api.ts
index 97c6fe5..fe44d66 100644
--- a/web/frontend/src/api.ts
+++ b/web/frontend/src/api.ts
@@ -122,6 +122,7 @@ export interface Task {
   feedback?: string | null
   created_at: string
   updated_at: string
+  completed_at?: string | null
 }
 
 export interface Decision {
diff --git a/web/frontend/src/locales/en.json b/web/frontend/src/locales/en.json
index 9a8724b..a3eab4f 100644
--- a/web/frontend/src/locales/en.json
+++ b/web/frontend/src/locales/en.json
@@ -221,7 +221,9 @@
     "settings_integrations_section": "Integrations",
     "settings_execution_mode": "Execution mode",
     "settings_autocommit": "Autocommit",
-    "settings_autocommit_hint": "— git commit after pipeline"
+    "settings_autocommit_hint": "— git commit after pipeline",
+    "done_date_from": "From",
+    "done_date_to": "To"
   },
   "escalation": {
     "watchdog_blocked": "Watchdog: task {task_id} blocked — {reason}",
diff --git a/web/frontend/src/locales/ru.json b/web/frontend/src/locales/ru.json
index 0eff34b..81c72e6 100644
--- a/web/frontend/src/locales/ru.json
+++ b/web/frontend/src/locales/ru.json
@@ -221,7 +221,9 @@
     "settings_integrations_section": "Интеграции",
     "settings_execution_mode": "Режим выполнения",
     "settings_autocommit": "Автокоммит",
-    "settings_autocommit_hint": "— git commit после pipeline"
+    "settings_autocommit_hint": "— git commit после pipeline",
+    "done_date_from": "От",
+    "done_date_to": "До"
   },
   "escalation": {
     "watchdog_blocked": "Watchdog: задача {task_id} заблокирована — {reason}",
diff --git a/web/frontend/src/views/ProjectView.vue b/web/frontend/src/views/ProjectView.vue
index 46051f8..5f13d48 100644
--- a/web/frontend/src/views/ProjectView.vue
+++ b/web/frontend/src/views/ProjectView.vue
@@ -186,6 +186,8 @@ function initStatusFilter(): string[] {
 const selectedStatuses = ref<string[]>(initStatusFilter())
 const selectedCategory = ref('')
 const taskSearch = ref('')
+const dateFrom = ref('')
+const dateTo = ref('')
 
 function toggleStatus(s: string) {
   const idx = selectedStatuses.value.indexOf(s)
@@ -659,6 +661,16 @@ const filteredTasks = computed(() => {
   let tasks = searchFilteredTasks.value
   if (selectedStatuses.value.length > 0) tasks = tasks.filter(t => selectedStatuses.value.includes(t.status))
   if (selectedCategory.value) tasks = tasks.filter(t => t.category === selectedCategory.value)
+  if ((dateFrom.value || dateTo.value) && selectedStatuses.value.includes('done')) {
+    tasks = tasks.filter(t => {
+      if (t.status !== 'done') return true
+      const dateStr = (t.completed_at || t.updated_at) ?? ''
+      const d = dateStr.substring(0, 10)
+      if (dateFrom.value && d < dateFrom.value) return false
+      if (dateTo.value && d > dateTo.value) return false
+      return true
+    })
+  }
   return tasks
 })
 
@@ -1077,6 +1089,17 @@ async function addDecision() {
           <button v-if="taskSearch" @click="taskSearch = ''"
             class="text-gray-600 hover:text-red-400 text-xs px-1">✕</button>
         </div>
+        <!-- Date filter for done tasks -->
+        <div v-if="selectedStatuses.includes('done')" class="flex items-center gap-2">
+          <span class="text-xs text-gray-600">{{ t('projectView.done_date_from') }}</span>
+          <input type="date" v-model="dateFrom" data-testid="date-from"
+            class="bg-gray-800 border border-gray-700 rounded px-2 py-0.5 text-xs text-gray-300 focus:border-gray-500 outline-none" />
+          <span class="text-xs text-gray-600">{{ t('projectView.done_date_to') }}</span>
+          <input type="date" v-model="dateTo" data-testid="date-to"
+            class="bg-gray-800 border border-gray-700 rounded px-2 py-0.5 text-xs text-gray-300 focus:border-gray-500 outline-none" />
+          <button v-if="dateFrom || dateTo" @click="dateFrom = ''; dateTo = ''"
+            class="text-gray-600 hover:text-red-400 text-xs px-1">✕</button>
+        </div>
       </div>
       <!-- Manual escalation tasks -->
       <div v-if="manualEscalationTasks.length" class="mb-4">