diff --git a/src/calendar/widgets/MonthCalendar.py b/src/calendar/widgets/MonthCalendar.py
index ee9907e..58dbcc0 100644
--- a/src/calendar/widgets/MonthCalendar.py
+++ b/src/calendar/widgets/MonthCalendar.py
@@ -16,15 +16,21 @@ from textual.reactive import reactive
 from textual.strip import Strip
 from textual.widget import Widget
 
+from src.calendar import config
 
-def get_month_calendar(year: int, month: int) -> list[list[Optional[date]]]:
+
+def get_month_calendar(
+    year: int, month: int, week_start_day: int = 0
+) -> list[list[Optional[date]]]:
     """Generate a calendar grid for a month.
 
     Returns a list of weeks, where each week is a list of 7 dates (or None for empty cells).
-    Week starts on Monday.
-    """
-    import calendar
 
+    Args:
+        year: The year
+        month: The month (1-12)
+        week_start_day: Config format (0=Sunday, 1=Monday, ..., 6=Saturday)
+    """
     # Get first day of month and number of days
     first_day = date(year, month, 1)
     if month == 12:
@@ -32,11 +38,17 @@ def get_month_calendar(year: int, month: int) -> list[list[Optional[date]]]:
     else:
         last_day = date(year, month + 1, 1) - timedelta(days=1)
 
-    # Monday = 0, Sunday = 6
-    first_weekday = first_day.weekday()
+    # Convert config week start to python weekday
+    # Config: 0=Sunday, 1=Monday, ..., 6=Saturday
+    # Python: 0=Monday, 1=Tuesday, ..., 6=Sunday
+    python_week_start = (week_start_day - 1) % 7
+
+    # Calculate which day of the week the first day falls on (relative to week start)
+    first_python_weekday = first_day.weekday()  # 0=Monday, 6=Sunday
+    days_offset = (first_python_weekday - python_week_start) % 7
 
     weeks: list[list[Optional[date]]] = []
-    current_week: list[Optional[date]] = [None] * first_weekday
+    current_week: list[Optional[date]] = [None] * days_offset
 
     current = first_day
     while current <= last_day:
@@ -55,6 +67,22 @@ def get_month_calendar(year: int, month: int) -> list[list[Optional[date]]]:
     return weeks
 
 
+def get_day_names(week_start_day: int = 0) -> str:
+    """Get day name headers based on week start day.
+
+    Args:
+        week_start_day: Config format (0=Sunday, 1=Monday, ..., 6=Saturday)
+
+    Returns:
+        String like "Su Mo Tu We Th Fr Sa" or "Mo Tu We Th Fr Sa Su"
+    """
+    # Full list starting from Sunday (config day 0)
+    all_days = ["Su", "Mo", "Tu", "We", "Th", "Fr", "Sa"]
+    # Rotate to start from week_start_day
+    rotated = all_days[week_start_day:] + all_days[:week_start_day]
+    return " ".join(rotated)
+
+
 class MonthCalendar(Widget):
     """A compact month calendar widget for sidebars."""
 
@@ -122,7 +150,11 @@ class MonthCalendar(Widget):
     @property
     def _weeks(self) -> list[list[Optional[date]]]:
         """Get the weeks for the current display month."""
-        return get_month_calendar(self.display_month.year, self.display_month.month)
+        return get_month_calendar(
+            self.display_month.year,
+            self.display_month.month,
+            config.week_start_day(),
+        )
 
     def get_content_height(self, container, viewport, width: int) -> int:
         """Calculate height: header + day names + weeks."""
@@ -152,8 +184,8 @@ class MonthCalendar(Widget):
         return Strip([Segment(header, style)])
 
     def _render_day_names(self) -> Strip:
-        """Render the day name headers (Mo Tu We ...)."""
-        day_names = "Mo Tu We Th Fr Sa Su"
+        """Render the day name headers based on week start setting."""
+        day_names = get_day_names(config.week_start_day())
         # Pad to widget width
         line = day_names[: self.size.width].ljust(self.size.width)
         style = Style(color="bright_black")