diff --git a/app/models/notification.py b/app/models/notification.py
index 6ec4d9b..afd524c 100644
--- a/app/models/notification.py
+++ b/app/models/notification.py
@@ -1,12 +1,12 @@
 """Notification model and notification-type catalog.
 
-A persisted per-user notification produced through the single ``notify()``
+A persisted per-user notification produced through the single `notify()`
 service. Notification types are shared with the notification wiring (149) and
 the preference model (150) so opt-outs map 1:1 to the types the app produces.
 
-Security: ``payload`` must never contain secrets, invitation tokens, or another
+Security: `payload` must never contain secrets, invitation tokens, or another
 user's data. Users can only ever read their own notifications (enforced by the
-notification API which always filters on ``current_user.id``).
+notification API which always filters on `current_user.id`).
 """
 
 from __future__ import annotations
@@ -21,6 +21,7 @@
 NOTIF_ROLE_CHANGE = "role_change"
 NOTIF_AI_EVENT = "ai_event"
 NOTIF_SHARE = "share"
+NOTIF_BUDGET_ALERT = "budget_alert"
 
 # Notification types that are always delivered: users cannot disable security-
 # critical system notifications about their own access.
@@ -31,6 +32,7 @@
     NOTIF_ROLE_CHANGE,
     NOTIF_AI_EVENT,
     NOTIF_SHARE,
+    NOTIF_BUDGET_ALERT,
 )
 
 
diff --git a/app/services/token_usage.py b/app/services/token_usage.py
index cdf1e12..1d398e7 100644
--- a/app/services/token_usage.py
+++ b/app/services/token_usage.py
@@ -13,7 +13,7 @@
 
 
 def estimate_tokens(text) -> int:
-    """Estimate the token count of ``text`` (>= 1 for non-empty input)."""
+    """Estimate the token count of `text` (>= 1 for non-empty input)."""
     if text is None:
         return 0
     value = str(text)
@@ -67,7 +67,7 @@ def usage_from_text(prompt_text, completion_text) -> dict:
 
 
 def sum_usage(messages) -> dict:
-    """Cumulative usage across ``messages`` (missing counts ignored)."""
+    """Cumulative usage across `messages` (missing counts ignored)."""
     prompt = completion = total = 0
     for message in messages or []:
         if getattr(message, "total_tokens", None) is None:
@@ -76,3 +76,45 @@ def sum_usage(messages) -> dict:
         completion += message.completion_tokens or 0
         total += message.total_tokens or 0
     return _totals(prompt, completion)
+
+
+class BudgetAlertDeduplicator:
+    """Per-period deduplication of budge threshold alerts.
+
+    A given threshold alert fires at most once per budget per period. The
+    deduplicator records the period in which each threshold was alerted and
+    suppresses repeated crossings within that period. Starting a new period
+    resets the recorded alerts so the threshold can fire again.
+    """
+
+    def __init__(self):
+        self._period = None
+        self._alerted = set()
+
+    def _ensure_period(self, period) -> None:
+        if period != self._period:
+            self._period = period
+            self._alerted = set()
+
+    def should_alert(self, period, threshold) -> bool:
+        """Return True if the alert has not yet fired for this period/threshold."""
+        self._ensure_period(period)
+        return threshold not in self._alerted
+
+    def mark_alerted(self, period, threshold) -> None:
+        """Record that the alert fired for this period/threshold."""
+        self._ensure_period(period)
+        self._alerted.add(threshold)
+
+    def check_and_mark(self, period, threshold) -> bool:
+        """Atomically check and record the alert; True if it should fire."""
+        self._ensure_period(period)
+        if threshold in self._alerted:
+            return False
+        self._alerted.add(threshold)
+        return True
+
+    def reset(self, period=None) -> None:
+        """Clear recorded alerts, optionally switching to a new period."""
+        self._period = period
+        self._alerted = set()
diff --git a/tests/test_notifications.py b/tests/test_notifications.py
index d62b309..df144a8 100644
--- a/tests/test_notifications.py
+++ b/tests/test_notifications.py
@@ -167,3 +167,30 @@ def test_remove_member_creates_membership_notification(self, client, make_user,
 
         created = Notification.query.filter_by(user_id=member.id, type="membership").one()
         assert created.is_read is False
+
+
+class TestBudgetAlertDeduplication:
+    def test_repeated_crossings_alert_once_per_period(self, app, make_user):
+        from app.services.budget_alerts import check_budget_alerts
+
+        user = make_user()
+        workspace = Workspace(user_id=user.id, name="Budget ws")
+        db.session.add(workspace)
+        db.session.commit()
+
+        alerts = check_budget_alerts(workspace.id, spend=150, limit=100, period="2024-01")
+        assert len(alerts) == 1
+        alerts = check_budget_alerts(workspace.id, spend=150, limit=100, period="2024-01")
+        assert len(alerts) == 0
+
+    def test_new_period_resets_deduplication(self/ app, make_user):
+        from app.services.budget_alerts import check_budget_alerts
+
+        user = make_user()
+        workspace = Workspace(user_id=user.id, name="Budget ws")
+        db.session.add(workspace)
+        db.session.commit()
+
+        assert len(check_budget_alerts(workspace.id, spend=150, limit=100, period="2024-01")) == 1
+        assert len(check_budget_alerts(workspace.id, spend=150, limit=100, period="2024-01")) == 0
+        assert len(check_budget_alerts(workspace.id, spend=150, limit=100, period="2024-02")) == 1