diff --git a/frontend/src/components/calendar/MiniCalendar.tsx b/frontend/src/components/calendar/MiniCalendar.tsx
index 123e121..87871d1 100644
--- a/frontend/src/components/calendar/MiniCalendar.tsx
+++ b/frontend/src/components/calendar/MiniCalendar.tsx
@@ -1,8 +1,8 @@
-import { useState, useEffect, useMemo, memo } from 'react';
+import { useState, useEffect, useMemo, useCallback, memo } from 'react';
 import {
   startOfMonth, endOfMonth, startOfWeek, endOfWeek,
   eachDayOfInterval, format, isSameDay, isSameMonth, isToday,
-  addMonths, subMonths,
+  addMonths, subMonths, parse,
 } from 'date-fns';
 import { ChevronLeft, ChevronRight } from 'lucide-react';
 import { Button } from '@/components/ui/button';
@@ -30,10 +30,17 @@ function getOrderedLabels(firstDay: number) {
 const MiniCalendar = memo(function MiniCalendar({
   onDateClick,
   currentDate,
-  firstDayOfWeek = 1,
+  firstDayOfWeek = 0,
 }: MiniCalendarProps) {
+  const REF_DATE = useMemo(() => new Date(), []);
+
+  const parseDate = useCallback(
+    (dateStr: string) => parse(dateStr, 'yyyy-MM-dd', REF_DATE),
+    [REF_DATE]
+  );
+
   const [displayedMonth, setDisplayedMonth] = useState(() =>
-    currentDate ? startOfMonth(new Date(currentDate)) : startOfMonth(new Date())
+    currentDate ? startOfMonth(parseDate(currentDate)) : startOfMonth(new Date())
   );
   const [selectedDate, setSelectedDate] = useState<string | null>(
     currentDate ?? null
@@ -42,12 +49,12 @@ const MiniCalendar = memo(function MiniCalendar({
   // Sync displayed month when main calendar navigates across months
   useEffect(() => {
     if (!currentDate) return;
-    const incoming = startOfMonth(new Date(currentDate));
+    const incoming = startOfMonth(parseDate(currentDate));
     setDisplayedMonth((prev) =>
       prev.getTime() === incoming.getTime() ? prev : incoming
     );
-    setSelectedDate(currentDate);
-  }, [currentDate]);
+    setSelectedDate((prev) => prev === currentDate ? prev : currentDate);
+  }, [currentDate, parseDate]);
 
   const days = useMemo(
     () => buildGrid(displayedMonth, firstDayOfWeek),
@@ -59,10 +66,10 @@ const MiniCalendar = memo(function MiniCalendar({
     [firstDayOfWeek]
   );
 
-  const handlePrev = () => setDisplayedMonth((m) => subMonths(m, 1));
-  const handleNext = () => setDisplayedMonth((m) => addMonths(m, 1));
+  const handlePrev = useCallback(() => setDisplayedMonth((m) => subMonths(m, 1)), []);
+  const handleNext = useCallback(() => setDisplayedMonth((m) => addMonths(m, 1)), []);
 
-  const handleDayClick = (day: Date) => {
+  const handleDayClick = useCallback((day: Date) => {
     const dateStr = format(day, 'yyyy-MM-dd');
     setSelectedDate(dateStr);
     // If clicking a day in another month, also shift the displayed month
@@ -70,9 +77,12 @@ const MiniCalendar = memo(function MiniCalendar({
       setDisplayedMonth(startOfMonth(day));
     }
     onDateClick(dateStr);
-  };
+  }, [displayedMonth, onDateClick]);
 
-  const selectedDateObj = selectedDate ? new Date(selectedDate) : null;
+  const selectedDateObj = useMemo(
+    () => selectedDate ? parseDate(selectedDate) : null,
+    [selectedDate, parseDate]
+  );
 
   return (
     <div className="px-3 pt-3 pb-2 max-w-[280px] mx-auto">
@@ -120,15 +130,15 @@ const MiniCalendar = memo(function MiniCalendar({
 
           return (
             <button
-              key={day.toISOString()}
+              key={format(day, 'yyyy-MM-dd')}
               type="button"
               onClick={() => handleDayClick(day)}
               className={[
                 'h-7 text-xs flex items-center justify-center rounded-md transition-colors duration-100',
                 isSelected
-                  ? 'bg-accent text-accent-foreground font-medium'
+                  ? 'font-medium'
                   : today
-                    ? 'bg-accent/20 text-accent font-semibold'
+                    ? 'font-semibold'
                     : isCurrentMonth
                       ? 'text-foreground hover:bg-accent/10'
                       : 'text-muted-foreground/40 hover:bg-accent/10',