diff --git a/tests/test_trials.py b/tests/test_trials.py
index 21df0fb..8029fe3 100644
--- a/tests/test_trials.py
+++ b/tests/test_trials.py
@@ -25,3 +25,31 @@ def test_start_trial_is_idempotent_resets(tracker):
     tracker.start_trial("Some-Pack")
     tracker.start_trial("Some-Pack")
     assert len(tracker.get_trials()) == 1
+
+
+def _ahead(days):
+    return datetime.now(timezone.utc) + timedelta(days=days)
+
+
+def test_tick_increments_only_on_new_day(tracker):
+    tracker.start_trial("Pack")          # enable day, counter 0
+    tracker.tick_boot_days()             # same day -> no change
+    assert tracker.get_trials()[0]["unused_boot_days"] == 0
+
+    with patch("tracker.datetime") as m:
+        m.now.return_value = _ahead(1)
+        tracker.tick_boot_days()         # new day -> 1
+        tracker.tick_boot_days()         # same (mocked) day -> still 1
+    assert tracker.get_trials()[0]["unused_boot_days"] == 1
+
+
+def test_tick_reaches_expiry(tracker):
+    tracker.start_trial("Pack")
+    for d in range(1, DEFAULT_TRIAL_BUDGET + 1):
+        with patch("tracker.datetime") as m:
+            m.now.return_value = _ahead(d)
+            tracker.tick_boot_days()
+    t = tracker.get_trials()[0]
+    assert t["unused_boot_days"] == DEFAULT_TRIAL_BUDGET
+    assert t["expired"] is True
+    assert t["days_remaining"] == 0
diff --git a/tracker.py b/tracker.py
index ef27109..76ce991 100644
--- a/tracker.py
+++ b/tracker.py
@@ -432,6 +432,24 @@ class UsageTracker:
             result.append(d)
         return result
 
+    def tick_boot_days(self):
+        """Once per distinct calendar day, age every active trial by one boot-day."""
+        today = datetime.now(timezone.utc).date().isoformat()
+        with self._lock:
+            self._ensure_db()
+            conn = self._connect()
+            try:
+                conn.execute(
+                    """UPDATE trial_packages
+                       SET unused_boot_days = unused_boot_days + 1,
+                           last_boot_day = ?
+                       WHERE last_boot_day != ?""",
+                    (today, today),
+                )
+                conn.commit()
+            finally:
+                conn.close()
+
     def reset(self):
         """Clear all tracked data."""
         with self._lock: