diff --git a/src/tool_implementations.py b/src/tool_implementations.py
index 09b0306..1ee61bf 100644
--- a/src/tool_implementations.py
+++ b/src/tool_implementations.py
@@ -1921,9 +1921,22 @@ async def do_manage_notes(content: str, owner: Optional[str] = None) -> Dict:
                 return {"error": f"Note '{note_id}' not found", "exit_code": 1}
             if owner is not None and note.owner and note.owner != owner:
                 return {"error": "Note not found", "exit_code": 1}
-            for field in ("title", "content", "note_type", "color", "label", "due_date"):
+            for field in ("title", "content", "note_type", "color", "label"):
                 if field in args and args[field] is not None:
                     setattr(note, field, args[field])
+            # Parse due_date the same way the `add` action does. The schema
+            # advertises natural language ("tomorrow at 9am"), and naive ISO
+            # strings need the user's tz offset attached so the frontend's
+            # `new Date()` resolves the right absolute moment. Storing the raw
+            # value here left updated reminders as unparseable literals that
+            # never fired.
+            if args.get("due_date") is not None:
+                due_raw = args["due_date"]
+                try:
+                    from routes.calendar_routes import parse_due_for_user as _pdt_user
+                    note.due_date = _pdt_user(due_raw)
+                except Exception:
+                    note.due_date = due_raw  # fall through; trust the model
             new_items = args.get("checklist_items")
             if new_items is None:
                 new_items = args.get("items")
diff --git a/tests/test_notes_update_due_date.py b/tests/test_notes_update_due_date.py
new file mode 100644
index 0000000..25a21b5
--- /dev/null
+++ b/tests/test_notes_update_due_date.py
@@ -0,0 +1,110 @@
+"""Regression: manage_notes `update` must parse due_date like `add` does.
+
+The `add` action runs due_date through `parse_due_for_user` (natural language
+like "tomorrow at 9am", plus user-tz anchoring for naive ISO). The `update`
+action stored the raw value verbatim, so a reminder edited with natural language
+was saved as an unparseable literal the frontend's `new Date()` can't read — and
+the reminder never fired. Both actions must route due_date through the parser.
+"""
+import asyncio
+import json
+import sys
+import types
+from types import SimpleNamespace
+from unittest.mock import MagicMock
+
+import pytest
+
+from src import tool_implementations
+
+
+def _install_fakes(monkeypatch, note, parse=None):
+    """Stub the modules do_manage_notes imports lazily at call time.
+
+    core.database opens a real sqlite file and routes.calendar_routes needs
+    dateutil, so we inject light fakes. We also pin sqlalchemy.orm.attributes
+    (for flag_modified): it imports fine in isolation, but other tests in the
+    suite replace sys.modules['sqlalchemy.orm'] with a non-package, so we make
+    this leaf import order-independent. Placing each leaf module in sys.modules
+    means the parent package is never re-imported.
+    """
+    fake_sa_attrs = types.ModuleType("sqlalchemy.orm.attributes")
+    fake_sa_attrs.flag_modified = lambda *a, **k: None
+    monkeypatch.setitem(sys.modules, "sqlalchemy.orm.attributes", fake_sa_attrs)
+
+    class FakeQuery:
+        def filter(self, *a, **k):
+            return self
+
+        def first(self):
+            return note
+
+    class FakeDB:
+        def query(self, *a, **k):
+            return FakeQuery()
+
+        def add(self, *a, **k):
+            pass
+
+        def commit(self):
+            pass
+
+        def close(self):
+            pass
+
+    fake_core_db = types.ModuleType("core.database")
+    fake_core_db.SessionLocal = lambda: FakeDB()
+    fake_core_db.Note = MagicMock()  # only used as a query/filter argument
+    monkeypatch.setitem(sys.modules, "core.database", fake_core_db)
+
+    calls = {"parsed": []}
+
+    def _default_parse(s):
+        calls["parsed"].append(s)
+        return "PARSED::" + s
+
+    fake_cal = types.ModuleType("routes.calendar_routes")
+    fake_cal.parse_due_for_user = parse or _default_parse
+    monkeypatch.setitem(sys.modules, "routes.calendar_routes", fake_cal)
+    return calls
+
+
+def _run_update(args):
+    return asyncio.run(tool_implementations.do_manage_notes(json.dumps(args), owner=None))
+
+
+def test_update_parses_natural_language_due_date(monkeypatch):
+    note = SimpleNamespace(
+        id="abc12345-existing", owner=None, title="Dentist", content=None,
+        note_type="note", color=None, label=None, items=None,
+        pinned=False, archived=False, due_date=None,
+    )
+    calls = _install_fakes(monkeypatch, note)
+
+    result = _run_update(
+        {"action": "update", "id": "abc12345", "due_date": "tomorrow at 9am"}
+    )
+
+    assert result.get("exit_code") == 0
+    # Stored value went through the parser, not the raw literal.
+    assert note.due_date == "PARSED::tomorrow at 9am"
+    assert calls["parsed"] == ["tomorrow at 9am"]
+
+
+def test_update_still_sets_other_fields_without_parsing_them(monkeypatch):
+    note = SimpleNamespace(
+        id="abc12345-existing", owner=None, title="Old", content=None,
+        note_type="note", color=None, label=None, items=None,
+        pinned=False, archived=False, due_date=None,
+    )
+    calls = _install_fakes(monkeypatch, note)
+
+    result = _run_update(
+        {"action": "update", "id": "abc12345", "title": "New", "label": "home"}
+    )
+
+    assert result.get("exit_code") == 0
+    assert note.title == "New"
+    assert note.label == "home"
+    # No due_date supplied → the parser is not invoked.
+    assert calls["parsed"] == []