diff --git a/routes/calendar_routes.py b/routes/calendar_routes.py
index bd2b443..137fde9 100644
--- a/routes/calendar_routes.py
+++ b/routes/calendar_routes.py
@@ -16,6 +16,23 @@ from src.auth_helpers import get_current_user, require_user
 
 logger = logging.getLogger(__name__)
 
+
+def _ics_naive_dtstart(dt):
+    """Naive value matching how import_ics STORES CalendarEvent.dtstart.
+
+    Timed tz-aware events are stored as UTC with tzinfo stripped, all-day
+    dates as midnight datetimes, naive datetimes unchanged. The ICS dedup
+    must compute the same value or a re-import never matches the stored row.
+    """
+    if isinstance(dt, datetime):
+        if dt.tzinfo is not None:
+            from datetime import timezone as _tz
+            return dt.astimezone(_tz.utc).replace(tzinfo=None)
+        return dt
+    if isinstance(dt, date):
+        return datetime(dt.year, dt.month, dt.day)
+    return dt
+
 # Single-user fallback identity. Used only when:
 #   1. The app is configured for single-user (no auth middleware), AND
 #   2. The request didn't resolve to an authenticated user.
@@ -1023,7 +1040,12 @@ def setup_calendar_routes() -> APIRouter:
                 source_uid = str(comp.get("uid", "")) or None
                 if source_uid:
                     src_dtstart = dtstart.dt
-                    naive_src = src_dtstart.replace(tzinfo=None) if hasattr(src_dtstart, 'tzinfo') and src_dtstart.tzinfo else src_dtstart
+                    # Normalize to the SAME naive form import_ics stores, so a
+                    # re-import of a tz-aware event matches the existing row.
+                    # The old code stripped tzinfo WITHOUT converting to UTC
+                    # (wall clock), while storage converts to UTC first, so
+                    # every re-import of a TZID event created a duplicate.
+                    naive_src = _ics_naive_dtstart(src_dtstart)
                     existing = (
                         db.query(CalendarEvent)
                         .filter(
diff --git a/tests/test_ics_import_dedup_tz.py b/tests/test_ics_import_dedup_tz.py
new file mode 100644
index 0000000..47c52fd
--- /dev/null
+++ b/tests/test_ics_import_dedup_tz.py
@@ -0,0 +1,43 @@
+"""ICS re-import must dedup tz-aware timed events.
+
+import_ics stores a tz-aware DTSTART as naive UTC (e.g. 09:00 America/
+New_York becomes 13:00), but the dedup key stripped tzinfo WITHOUT the UTC
+conversion (kept 09:00 wall clock). So the dedup query never matched the
+stored row and every re-import of a TZID event inserted a duplicate. The
+shared _ics_naive_dtstart helper now drives both.
+"""
+from datetime import date, datetime, timezone, timedelta
+
+import pytest
+
+pytest.importorskip("sqlalchemy")
+
+from routes.calendar_routes import _ics_naive_dtstart
+
+
+def test_tz_aware_dedup_key_matches_utc_storage_form():
+    zi = pytest.importorskip("zoneinfo")
+    ny = zi.ZoneInfo("America/New_York")
+    dt = datetime(2026, 6, 15, 9, 0, tzinfo=ny)  # EDT = UTC-4 -> 13:00 UTC
+    assert _ics_naive_dtstart(dt) == datetime(2026, 6, 15, 13, 0)
+
+
+def test_fixed_offset_dedup_key_is_utc():
+    dt = datetime(2026, 6, 15, 9, 0, tzinfo=timezone(timedelta(hours=2)))
+    assert _ics_naive_dtstart(dt) == datetime(2026, 6, 15, 7, 0)
+
+
+def test_naive_datetime_unchanged():
+    dt = datetime(2026, 6, 15, 9, 0)
+    assert _ics_naive_dtstart(dt) == dt
+
+
+def test_all_day_date_becomes_midnight_datetime():
+    assert _ics_naive_dtstart(date(2026, 6, 15)) == datetime(2026, 6, 15, 0, 0)
+
+
+def test_dedup_key_equals_storage_conversion():
+    zi = pytest.importorskip("zoneinfo")
+    dt_val = datetime(2026, 11, 1, 9, 30, tzinfo=zi.ZoneInfo("America/New_York"))
+    stored = dt_val.astimezone(timezone.utc).replace(tzinfo=None)
+    assert _ics_naive_dtstart(dt_val) == stored