diff --git a/selfprivacy_api/utils/time.py b/selfprivacy_api/utils/time.py
new file mode 100644
index 0000000..5eb7e04
--- /dev/null
+++ b/selfprivacy_api/utils/time.py
@@ -0,0 +1,30 @@
+from datetime import datetime, timezone
+
+
+def tzaware_parse_time(iso_timestamp: str) -> datetime:
+    """
+    parse an iso8601 timestamp into timezone-aware datetime
+    assume utc if no timezone in stamp
+    example of timestamp:
+    2023-11-10T12:07:47.868788+00:00
+
+    """
+    dt = datetime.fromisoformat(iso_timestamp)
+    if dt.tzinfo is None:
+        dt = dt.astimezone(timezone.utc)
+    return dt
+
+
+def tzaware_parse_time_strict(iso_timestamp: str) -> datetime:
+    """
+    parse an iso8601 timestamp into timezone-aware datetime
+    raise an error if no timezone in stamp
+    example of timestamp:
+    2023-11-10T12:07:47.868788+00:00
+
+    """
+    dt = datetime.fromisoformat(iso_timestamp)
+    if dt.tzinfo is None:
+        raise ValueError("no timezone in timestamp", iso_timestamp)
+        dt = dt.astimezone(timezone.utc)
+    return dt