diff --git a/src/textual/widgets/_month_calendar.py b/src/textual/widgets/_month_calendar.py
index 8d64f0d0e0..b3014039a7 100644
--- a/src/textual/widgets/_month_calendar.py
+++ b/src/textual/widgets/_month_calendar.py
@@ -6,6 +6,7 @@
 
 from rich.text import Text
 from textual.app import ComposeResult
+from textual.events import Mount
 from textual.reactive import Reactive
 from textual.widget import Widget
 from textual.widgets import DataTable
@@ -44,7 +45,7 @@ def __init__(
     def compose(self) -> ComposeResult:
         yield DataTable()
 
-    def on_mount(self) -> None:
+    def _on_mount(self, _: Mount) -> None:
         self._update_week_header()
         self._update_calendar_days()
 
@@ -98,12 +99,13 @@ def validate_first_weekday(self, first_weekday: int) -> int:
             )
         return first_weekday
 
-    # def watch_year(self) -> None:
-    #     self._update_calendar_days()
-    #
-    # def _watch_month(self) -> None:
-    #     self._update_calendar_days()
+    def watch_year(self) -> None:
+        self.call_after_refresh(self._update_calendar_days)
+
+    def watch_month(self) -> None:
+        self.call_after_refresh(self._update_calendar_days)
 
     # def watch_first_weekday(self) -> None:
-    #     self._calendar = calendar.Calendar(self.firstweekday)
+    #     self._calendar = calendar.Calendar(self.first_weekday)
     #     self._update_week_header()
+    #     self._update_calendar_days()
diff --git a/tests/test_month_calendar.py b/tests/test_month_calendar.py
index f92fd58d80..91d3ed5af6 100644
--- a/tests/test_month_calendar.py
+++ b/tests/test_month_calendar.py
@@ -48,6 +48,7 @@ async def test_calendar_table_week_header():
     app = MonthCalendarApp()
     async with app.run_test() as pilot:
         month_calendar = pilot.app.query_one(MonthCalendar)
+        await pilot.pause()
         table = month_calendar.query_one(DataTable)
         actual_labels = [col.label.plain for col in table.columns.values()]
         expected_labels = ["Mon", "Tue", "Wed", "Thu", "Fri", "Sat", "Sun"]
@@ -58,6 +59,7 @@ async def test_calendar_table_days():
     app = MonthCalendarApp()
     async with app.run_test() as pilot:
         month_calendar = pilot.app.query_one(MonthCalendar)
+        await pilot.pause()
         table = month_calendar.query_one(DataTable)
         for row, week in enumerate(month_calendar.calendar_dates):
             for column, date in enumerate(week):
@@ -66,9 +68,45 @@ async def test_calendar_table_days():
                 assert actual_day == expected_day
 
 
-# async def test_calendar_table_after_reactive_year_change():
-#     pass
+async def test_calendar_table_after_reactive_year_change():
+    app = MonthCalendarApp()
+    async with app.run_test() as pilot:
+        month_calendar = pilot.app.query_one(MonthCalendar)
+        month_calendar.year = 2023
+        await pilot.pause()
+        table = month_calendar.query_one(DataTable)
+        expected_first_monday = datetime.date(2023, 5, 29)
+        actual_first_monday = month_calendar.calendar_dates[0][0]
+        assert actual_first_monday == expected_first_monday
+        assert table.get_cell_at(Coordinate(0, 0)).plain == "29"
+
+
+async def test_calendar_table_after_reactive_month_change():
+    app = MonthCalendarApp()
+    async with app.run_test() as pilot:
+        month_calendar = pilot.app.query_one(MonthCalendar)
+        month_calendar.month = 7
+        await pilot.pause()
+        table = month_calendar.query_one(DataTable)
+        expected_first_monday = datetime.date(2021, 6, 28)
+        actual_first_monday = month_calendar.calendar_dates[0][0]
+        assert actual_first_monday == expected_first_monday
+        assert table.get_cell_at(Coordinate(0, 0)).plain == "28"
+
+
+# async def test_calendar_table_after_reactive_first_weekday_change():
+#     app = MonthCalendarApp()
+#     async with app.run_test() as pilot:
+#         month_calendar = pilot.app.query_one(MonthCalendar)
+#         month_calendar.first_weekday = 6  # Sunday
+#         await pilot.pause()
+#         table = month_calendar.query_one(DataTable)
 #
+#         actual_labels = [col.label.plain for col in table.columns.values()]
+#         expected_labels = ["Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"]
+#         assert actual_labels == expected_labels
 #
-# async def test_calendar_table_after_reactive_month_change():
-#     pass
+#         expected_first_sunday = datetime.date(2021, 5, 30)
+#         actual_first_sunday = month_calendar.calendar_dates[0][0]
+#         assert actual_first_sunday == expected_first_sunday
+#         assert table.get_cell_at(Coordinate(0, 0)).plain == "30"