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/tests/test_kin_126_regression.py b/tests/test_kin_126_regression.py
new file mode 100644
index 0000000..5c1a56d
--- /dev/null
+++ b/tests/test_kin_126_regression.py
@@ -0,0 +1,108 @@
+"""Regression tests for KIN-126 — фильтр по дате выполнения задач.
+
+Проверяет backend-поведение:
+1. Колонка completed_at добавляется в таблицу tasks при инициализации БД
+2. Новая задача имеет completed_at=None по умолчанию
+3. update_task(status='done') устанавливает completed_at как ISO-строку
+4. update_task(status='done') — completed_at является валидной ISO-строкой
+5. update_task(status='in_progress') не устанавливает completed_at
+6. update_task(status='cancelled') не устанавливает completed_at
+7. Обновление полей без смены статуса на done не трогает completed_at
+8. update_task(status='blocked') не устанавливает completed_at
+"""
+
+import pytest
+from datetime import datetime
+from core.db import init_db
+from core import models
+
+
+@pytest.fixture
+def conn():
+    """Fresh in-memory DB for each test."""
+    c = init_db(db_path=":memory:")
+    yield c
+    c.close()
+
+
+# ---------------------------------------------------------------------------
+# Schema
+# ---------------------------------------------------------------------------
+
+def test_schema_tasks_has_completed_at_column(conn):
+    """KIN-126: таблица tasks содержит колонку completed_at после инициализации БД."""
+    cols = {r[1] for r in conn.execute("PRAGMA table_info(tasks)").fetchall()}
+    assert "completed_at" in cols, "KIN-126: колонка completed_at должна быть в таблице tasks"
+
+
+# ---------------------------------------------------------------------------
+# Default value
+# ---------------------------------------------------------------------------
+
+def test_new_task_completed_at_is_null(conn):
+    """KIN-126: новая задача имеет completed_at=None по умолчанию."""
+    models.create_project(conn, "p1", "P1", "/p1")
+    t = models.create_task(conn, "P1-001", "p1", "Task")
+    assert t["completed_at"] is None
+
+
+# ---------------------------------------------------------------------------
+# Setting completed_at on status='done'
+# ---------------------------------------------------------------------------
+
+def test_update_task_to_done_sets_completed_at(conn):
+    """KIN-126: update_task(status='done') устанавливает completed_at."""
+    models.create_project(conn, "p1", "P1", "/p1")
+    models.create_task(conn, "P1-001", "p1", "Task")
+    updated = models.update_task(conn, "P1-001", status="done")
+    assert updated["completed_at"] is not None
+
+
+def test_update_task_to_done_completed_at_is_valid_iso(conn):
+    """KIN-126: completed_at при status='done' — валидная ISO-строка datetime."""
+    models.create_project(conn, "p1", "P1", "/p1")
+    models.create_task(conn, "P1-001", "p1", "Task")
+    updated = models.update_task(conn, "P1-001", status="done")
+    # Must parse without exception
+    parsed = datetime.fromisoformat(updated["completed_at"])
+    assert parsed is not None
+
+
+# ---------------------------------------------------------------------------
+# Non-done statuses do NOT set completed_at
+# ---------------------------------------------------------------------------
+
+def test_update_task_to_in_progress_does_not_set_completed_at(conn):
+    """KIN-126: update_task(status='in_progress') не устанавливает completed_at."""
+    models.create_project(conn, "p1", "P1", "/p1")
+    models.create_task(conn, "P1-001", "p1", "Task")
+    updated = models.update_task(conn, "P1-001", status="in_progress")
+    assert updated["completed_at"] is None
+
+
+def test_update_task_to_cancelled_does_not_set_completed_at(conn):
+    """KIN-126: update_task(status='cancelled') не устанавливает completed_at."""
+    models.create_project(conn, "p1", "P1", "/p1")
+    models.create_task(conn, "P1-001", "p1", "Task")
+    updated = models.update_task(conn, "P1-001", status="cancelled")
+    assert updated["completed_at"] is None
+
+
+def test_update_task_to_blocked_does_not_set_completed_at(conn):
+    """KIN-126: update_task(status='blocked') не устанавливает completed_at."""
+    models.create_project(conn, "p1", "P1", "/p1")
+    models.create_task(conn, "P1-001", "p1", "Task")
+    updated = models.update_task(conn, "P1-001", status="blocked")
+    assert updated["completed_at"] is None
+
+
+# ---------------------------------------------------------------------------
+# Non-status updates do NOT touch completed_at
+# ---------------------------------------------------------------------------
+
+def test_update_task_priority_only_does_not_set_completed_at(conn):
+    """KIN-126: update_task с изменением только priority не трогает completed_at."""
+    models.create_project(conn, "p1", "P1", "/p1")
+    models.create_task(conn, "P1-001", "p1", "Task")
+    updated = models.update_task(conn, "P1-001", priority=1)
+    assert updated["completed_at"] is None
diff --git a/web/frontend/src/__tests__/date-filter.test.ts b/web/frontend/src/__tests__/date-filter.test.ts
new file mode 100644
index 0000000..869308a
--- /dev/null
+++ b/web/frontend/src/__tests__/date-filter.test.ts
@@ -0,0 +1,283 @@
+/**
+ * KIN-126: Тесты фильтра по дате выполнения задач (done tasks date range filter)
+ *
+ * AC: фильтр сделан и работает
+ *
+ * Проверяет:
+ * 1. Date filter inputs отображаются только когда выбран статус 'done'
+ * 2. Date filter inputs скрыты на других статусах
+ * 3. Date filter inputs скрыты без фильтра статуса
+ * 4. Фильтрация по dateFrom — задачи до этой даты исключаются
+ * 5. Фильтрация по dateTo — задачи после этой даты исключаются
+ * 6. Пустой результат при несовпадении дат
+ * 7. Сброс фильтра (кнопка ✕) показывает все done-задачи снова
+ * 8. Fallback на updated_at когда completed_at=null
+ */
+
+import { describe, it, expect, vi, beforeEach } from 'vitest'
+import { mount, flushPromises } from '@vue/test-utils'
+import { createRouter, createMemoryHistory } from 'vue-router'
+import ProjectView from '../views/ProjectView.vue'
+
+vi.mock('../api', () => ({
+  api: {
+    project: vi.fn(),
+    taskFull: vi.fn(),
+    runTask: vi.fn(),
+    auditProject: vi.fn(),
+    createTask: vi.fn(),
+    patchTask: vi.fn(),
+    patchProject: vi.fn(),
+    deployProject: vi.fn(),
+  },
+}))
+
+import { api } from '../api'
+
+const Stub = { template: '<div />' }
+
+function makeTask(
+  id: string,
+  status: string,
+  completedAt: string | null,
+  updatedAt = '2024-01-10T00:00:00',
+) {
+  return {
+    id,
+    project_id: 'KIN',
+    title: `Task ${id}`,
+    status,
+    priority: 5,
+    assigned_role: null,
+    parent_task_id: null,
+    brief: null,
+    spec: null,
+    created_at: '2024-01-01T00:00:00',
+    updated_at: updatedAt,
+    completed_at: completedAt,
+  }
+}
+
+const MOCK_PROJECT_DATE_FILTER = {
+  id: 'KIN',
+  name: 'Kin',
+  path: '/projects/kin',
+  status: 'active',
+  priority: 5,
+  tech_stack: ['python', 'vue'],
+  created_at: '2024-01-01',
+  total_tasks: 4,
+  done_tasks: 3,
+  active_tasks: 1,
+  blocked_tasks: 0,
+  review_tasks: 0,
+  tasks: [
+    makeTask('KIN-001', 'done', '2024-01-05T12:00:00'),  // before range
+    makeTask('KIN-002', 'done', '2024-01-15T12:00:00'),  // in middle
+    makeTask('KIN-003', 'done', '2024-01-25T12:00:00'),  // after range
+    makeTask('KIN-004', 'pending', null),
+  ],
+  decisions: [],
+  modules: [],
+}
+
+function makeRouter() {
+  return createRouter({
+    history: createMemoryHistory(),
+    routes: [
+      { path: '/', component: Stub },
+      { path: '/project/:id', component: ProjectView, props: true },
+    ],
+  })
+}
+
+const localStorageMock = (() => {
+  let store: Record<string, string> = {}
+  return {
+    getItem: (k: string) => store[k] ?? null,
+    setItem: (k: string, v: string) => { store[k] = v },
+    removeItem: (k: string) => { delete store[k] },
+    clear: () => { store = {} },
+  }
+})()
+Object.defineProperty(globalThis, 'localStorage', { value: localStorageMock, configurable: true })
+
+beforeEach(() => {
+  localStorageMock.clear()
+  vi.mocked(api.project).mockResolvedValue(MOCK_PROJECT_DATE_FILTER as any)
+})
+
+describe('KIN-126: фильтр по дате выполнения задач', () => {
+  it('1. Date filter inputs отображаются когда выбран статус done', async () => {
+    const router = makeRouter()
+    await router.push('/project/KIN?status=done')
+
+    const wrapper = mount(ProjectView, {
+      props: { id: 'KIN' },
+      global: { plugins: [router] },
+    })
+    await flushPromises()
+
+    expect(
+      wrapper.find('[data-testid="date-from"]').exists(),
+      'date-from должен быть виден при status=done',
+    ).toBe(true)
+    expect(
+      wrapper.find('[data-testid="date-to"]').exists(),
+      'date-to должен быть виден при status=done',
+    ).toBe(true)
+  })
+
+  it('2. Date filter inputs скрыты когда done не выбран', async () => {
+    const router = makeRouter()
+    await router.push('/project/KIN?status=pending')
+
+    const wrapper = mount(ProjectView, {
+      props: { id: 'KIN' },
+      global: { plugins: [router] },
+    })
+    await flushPromises()
+
+    expect(
+      wrapper.find('[data-testid="date-from"]').exists(),
+      'date-from не должен быть виден при status=pending',
+    ).toBe(false)
+    expect(
+      wrapper.find('[data-testid="date-to"]').exists(),
+      'date-to не должен быть виден при status=pending',
+    ).toBe(false)
+  })
+
+  it('3. Date filter inputs скрыты без фильтра статуса', async () => {
+    const router = makeRouter()
+    await router.push('/project/KIN')
+
+    const wrapper = mount(ProjectView, {
+      props: { id: 'KIN' },
+      global: { plugins: [router] },
+    })
+    await flushPromises()
+
+    expect(
+      wrapper.find('[data-testid="date-from"]').exists(),
+      'date-from не должен быть виден без фильтра статуса',
+    ).toBe(false)
+  })
+
+  it('4. Фильтрация по dateFrom исключает задачи выполненные до этой даты', async () => {
+    const router = makeRouter()
+    await router.push('/project/KIN?status=done')
+
+    const wrapper = mount(ProjectView, {
+      props: { id: 'KIN' },
+      global: { plugins: [router] },
+    })
+    await flushPromises()
+
+    await wrapper.find('[data-testid="date-from"]').setValue('2024-01-10')
+    await flushPromises()
+
+    const links = wrapper.findAll('a[href^="/task/"]')
+    const ids = links.map(l => l.attributes('href')?.replace('/task/', '').split('?')[0])
+
+    expect(ids, 'KIN-001 (2024-01-05) должен быть исключён').not.toContain('KIN-001')
+    expect(ids, 'KIN-002 (2024-01-15) должен быть виден').toContain('KIN-002')
+    expect(ids, 'KIN-003 (2024-01-25) должен быть виден').toContain('KIN-003')
+  })
+
+  it('5. Фильтрация по dateTo исключает задачи выполненные после этой даты', async () => {
+    const router = makeRouter()
+    await router.push('/project/KIN?status=done')
+
+    const wrapper = mount(ProjectView, {
+      props: { id: 'KIN' },
+      global: { plugins: [router] },
+    })
+    await flushPromises()
+
+    await wrapper.find('[data-testid="date-to"]').setValue('2024-01-20')
+    await flushPromises()
+
+    const links = wrapper.findAll('a[href^="/task/"]')
+    const ids = links.map(l => l.attributes('href')?.replace('/task/', '').split('?')[0])
+
+    expect(ids, 'KIN-003 (2024-01-25) должен быть исключён').not.toContain('KIN-003')
+    expect(ids, 'KIN-001 (2024-01-05) должен быть виден').toContain('KIN-001')
+    expect(ids, 'KIN-002 (2024-01-15) должен быть виден').toContain('KIN-002')
+  })
+
+  it('6. Пустой результат когда ни одна задача не попадает в диапазон дат', async () => {
+    const router = makeRouter()
+    await router.push('/project/KIN?status=done')
+
+    const wrapper = mount(ProjectView, {
+      props: { id: 'KIN' },
+      global: { plugins: [router] },
+    })
+    await flushPromises()
+
+    await wrapper.find('[data-testid="date-from"]').setValue('2024-02-01')
+    await wrapper.find('[data-testid="date-to"]').setValue('2024-02-28')
+    await flushPromises()
+
+    const links = wrapper.findAll('a[href^="/task/"]')
+    expect(links, 'Ни одна done-задача не должна отображаться при несовпадении дат').toHaveLength(0)
+  })
+
+  it('7. Клик по кнопке сброса очищает фильтр и показывает все done-задачи', async () => {
+    const router = makeRouter()
+    await router.push('/project/KIN?status=done')
+
+    const wrapper = mount(ProjectView, {
+      props: { id: 'KIN' },
+      global: { plugins: [router] },
+    })
+    await flushPromises()
+
+    // Устанавливаем dateFrom — остаётся только одна done-задача
+    await wrapper.find('[data-testid="date-from"]').setValue('2024-01-20')
+    await flushPromises()
+    expect(wrapper.findAll('a[href^="/task/"]')).toHaveLength(1)
+
+    // Кнопка сброса — ✕ без data-action (не clear-status)
+    const resetBtn = wrapper.findAll('button').find(
+      b => b.text() === '✕' && !b.attributes('data-action'),
+    )
+    expect(resetBtn?.exists(), 'Кнопка сброса дат должна появиться').toBe(true)
+    await resetBtn!.trigger('click')
+    await flushPromises()
+
+    // После сброса — все 3 done-задачи видны
+    expect(wrapper.findAll('a[href^="/task/"]')).toHaveLength(3)
+  })
+
+  it('8. Fallback на updated_at когда completed_at=null', async () => {
+    const projectWithNullCompletedAt = {
+      ...MOCK_PROJECT_DATE_FILTER,
+      tasks: [
+        makeTask('KIN-010', 'done', null, '2024-01-05T00:00:00'),  // updated_at early
+        makeTask('KIN-011', 'done', null, '2024-01-25T00:00:00'),  // updated_at late
+      ],
+    }
+    vi.mocked(api.project).mockResolvedValue(projectWithNullCompletedAt as any)
+
+    const router = makeRouter()
+    await router.push('/project/KIN?status=done')
+
+    const wrapper = mount(ProjectView, {
+      props: { id: 'KIN' },
+      global: { plugins: [router] },
+    })
+    await flushPromises()
+
+    // dateFrom='2024-01-20' → KIN-010 (updated_at 2024-01-05) должен быть исключён
+    await wrapper.find('[data-testid="date-from"]').setValue('2024-01-20')
+    await flushPromises()
+
+    const links = wrapper.findAll('a[href^="/task/"]')
+    const ids = links.map(l => l.attributes('href')?.replace('/task/', '').split('?')[0])
+
+    expect(ids, 'KIN-010 должен быть исключён (updated_at до dateFrom)').not.toContain('KIN-010')
+    expect(ids, 'KIN-011 должен быть виден (updated_at после dateFrom)').toContain('KIN-011')
+  })
+})
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">