diff --git a/internals/maintenance_scripts.py b/internals/maintenance_scripts.py
index 628776bde238..2c6d999a4634 100644
--- a/internals/maintenance_scripts.py
+++ b/internals/maintenance_scripts.py
@@ -743,3 +743,61 @@ def get_template_data(self, **kwargs) -> str:
 
     ndb.put_multi(batch)
     return f'{count} Features entities updated.'
+
+
+class BackfillGateDates(FlaskHandler):
+
+  def get_template_data(self, **kwargs) -> str:
+    """Backfill resolved_on and needs_work_started_on for all Gates."""
+    self.require_cron_header()
+
+    count = 0
+    batch: list[Gate] = []
+    BATCH_SIZE = 100
+    votes_by_gate = collections.defaultdict(list)
+    for vote in Vote.query():
+      votes_by_gate[vote.gate_id].append(vote)
+    for gate in Gate.query():
+      gate_votes = votes_by_gate.get(gate.key.integer_id()) or []
+      if self.calc_dates(gate, gate_votes):
+        batch.append(gate)
+        count += 1
+        if len(batch) > BATCH_SIZE:
+          ndb.put_multi(batch)
+          batch = []
+
+    ndb.put_multi(batch)
+    return f'{count} Gate entities updated.'
+
+  def calc_dates(self, gate: Gate, votes: list[Vote]) -> bool:
+    """Set resolved_on and needs_work_started_on if needed."""
+    if not votes:
+      return False
+    new_resolved_on = self.calc_resolved_on(gate, votes)
+    new_needs_work_started_on = self.calc_needs_work_started_on(gate, votes)
+    if new_resolved_on is not None:
+      gate.resolved_on = new_resolved_on
+    if new_needs_work_started_on is not None:
+      gate.needs_work_started_on = new_needs_work_started_on
+    return bool(new_resolved_on or new_needs_work_started_on)
+
+  def calc_resolved_on(self, gate: Gate, votes: list[Vote]) -> datetime | None:
+    """Return the date on which the gate was resolved, or None."""
+    if gate.state not in Vote.FINAL_STATES:
+      return None
+    if gate.resolved_on:
+      return None
+
+    return max(v.set_on for v in votes
+               if v.state in Vote.FINAL_STATES)
+
+  def calc_needs_work_started_on(
+      self, gate: Gate, votes: list[Vote]) -> datetime | None:
+    """Return the latest date on which the gate entered NEEDS_WORK."""
+    if gate.state != Vote.NEEDS_WORK:
+      return None
+    if gate.needs_work_started_on:
+      return None
+
+    return max(v.set_on for v in votes
+               if v.state == Vote.NEEDS_WORK)
diff --git a/internals/maintenance_scripts_test.py b/internals/maintenance_scripts_test.py
index fba255b66581..7ba690c97847 100644
--- a/internals/maintenance_scripts_test.py
+++ b/internals/maintenance_scripts_test.py
@@ -757,3 +757,104 @@ def test_calc_all_shipping_years__some(self, mock_gasswm: mock.MagicMock):
     actual = self.handler.calc_all_shipping_years()
     expected = {22222: 2023, 33333: 2024, 44444: 2030}
     self.assertEqual(expected, actual)
+
+
+class BackfillGateDatesTest(testing_config.CustomTestCase):
+
+  def setUp(self):
+    self.gate = Gate(
+        feature_id=1, stage_id=2,
+        gate_type=core_enums.GATE_API_EXTEND_ORIGIN_TRIAL,
+        state=Gate.PREPARING)
+    self.handler = maintenance_scripts.BackfillGateDates()
+
+  def test_calc_resolved_on__not_resolved(self):
+    """If a gate is not resolved, don't set a resolved_on date."""
+    self.assertIsNone(
+        self.handler.calc_resolved_on(self.gate, []))
+
+    self.gate.state = Vote.REVIEW_REQUESTED
+    self.assertIsNone(
+        self.handler.calc_resolved_on(self.gate, []))
+
+    self.gate.state = Vote.NA_REQUESTED
+    self.assertIsNone(
+        self.handler.calc_resolved_on(self.gate, []))
+
+    self.gate.state = Vote.REVIEW_STARTED
+    self.assertIsNone(
+        self.handler.calc_resolved_on(self.gate, []))
+
+    self.gate.state = Vote.NEEDS_WORK
+    self.assertIsNone(
+        self.handler.calc_resolved_on(self.gate, []))
+
+  def test_calc_resolved_on__resolved(self):
+    """If a gate was resolved, resolved_on is the last approval."""
+    self.gate.state = Vote.APPROVED
+    gate_id = 1234
+    v1 = Vote(gate_id=gate_id, set_by='feature_owner@example.com',
+              state=Vote.REVIEW_REQUESTED,
+              set_on=datetime(2023, 1, 1, 12, 30, 0))
+    v2 = Vote(gate_id=gate_id, set_by='reviewer_a@example.com',
+              state=Vote.REVIEW_STARTED,
+              set_on=datetime(2023, 1, 2, 12, 30, 0))
+    v3 = Vote(gate_id=gate_id, set_by='reviewer_b@example.com',
+              state=Vote.APPROVED,
+              set_on=datetime(2023, 1, 3, 12, 30, 0))
+    v4 = Vote(gate_id=gate_id, set_by='reviewer_c@example.com',
+              state=Vote.APPROVED,
+              set_on=datetime(2023, 1, 4, 12, 30, 0))
+    v5 = Vote(gate_id=gate_id, set_by='reviewer_d@example.com',
+              state=Vote.REVIEW_STARTED,
+              set_on=datetime(2023, 1, 5, 12, 30, 0))
+
+    self.assertEqual(
+        self.handler.calc_resolved_on(self.gate, [v1, v2, v3, v4, v5]),
+        v4.set_on)
+
+  def test_calc_needs_work_started_on__not_needed(self):
+    """If a gate is not NEEDS_WORK, don't set a needs_work_started_on date."""
+    self.assertIsNone(
+        self.handler.calc_needs_work_started_on(self.gate, []))
+
+    self.gate.state = Vote.REVIEW_REQUESTED
+    self.assertIsNone(
+        self.handler.calc_needs_work_started_on(self.gate, []))
+
+    self.gate.state = Vote.NA_REQUESTED
+    self.assertIsNone(
+        self.handler.calc_needs_work_started_on(self.gate, []))
+
+    self.gate.state = Vote.REVIEW_STARTED
+    self.assertIsNone(
+        self.handler.calc_needs_work_started_on(self.gate, []))
+
+    self.gate.state = Vote.APPROVED
+    self.assertIsNone(
+        self.handler.calc_needs_work_started_on(self.gate, []))
+
+  def test_calc_needs_work_started_on__needed(self):
+    """If a gate is NEEDS_WORK, it started on the last NEEDS_WORK vote."""
+    self.gate.state = Vote.NEEDS_WORK
+    gate_id = 1234
+    v1 = Vote(gate_id=gate_id, set_by='feature_owner@example.com',
+              state=Vote.REVIEW_REQUESTED,
+              set_on=datetime(2023, 1, 1, 12, 30, 0))
+    v2 = Vote(gate_id=gate_id, set_by='reviewer_a@example.com',
+              state=Vote.NEEDS_WORK,
+              set_on=datetime(2023, 1, 2, 12, 30, 0))
+    v3 = Vote(gate_id=gate_id, set_by='reviewer_b@example.com',
+              state=Vote.APPROVED,
+              set_on=datetime(2023, 1, 3, 12, 30, 0))
+    v4 = Vote(gate_id=gate_id, set_by='reviewer_c@example.com',
+              state=Vote.NEEDS_WORK,
+              set_on=datetime(2023, 1, 4, 12, 30, 0))
+    v5 = Vote(gate_id=gate_id, set_by='reviewer_d@example.com',
+              state=Vote.REVIEW_STARTED,
+              set_on=datetime(2023, 1, 5, 12, 30, 0))
+
+    self.assertEqual(
+        self.handler.calc_needs_work_started_on(
+            self.gate, [v1, v2, v3, v4, v5]),
+        v4.set_on)
diff --git a/main.py b/main.py
index 232c68403f2b..0354fafedbdc 100644
--- a/main.py
+++ b/main.py
@@ -346,6 +346,8 @@ class Route:
         maintenance_scripts.DeleteEmptyExtensionStages),
   Route('/scripts/backfill_shipping_year',
         maintenance_scripts.BackfillShippingYear),
+  Route('/scripts/backfill_gate_dates',
+        maintenance_scripts.BackfillGateDates),
 ]
 
 dev_routes: list[Route] = []