diff --git a/frontend/src/components/calendar/CalendarPage.tsx b/frontend/src/components/calendar/CalendarPage.tsx
index 6331466..7fca355 100644
--- a/frontend/src/components/calendar/CalendarPage.tsx
+++ b/frontend/src/components/calendar/CalendarPage.tsx
@@ -90,12 +90,19 @@ export default function CalendarPage() {
 
   const panelOpen = panelMode !== 'closed';
 
-  // Resize calendar when panel opens/closes (CSS transition won't trigger ResizeObserver on inner div)
+  // Continuously resize calendar during panel open/close CSS transition
   useEffect(() => {
-    const timeout = setTimeout(() => {
+    let rafId: number;
+    const start = performance.now();
+    const duration = 350; // slightly longer than the 300ms CSS transition
+    const tick = () => {
       calendarRef.current?.getApi().updateSize();
-    }, 320);
-    return () => clearTimeout(timeout);
+      if (performance.now() - start < duration) {
+        rafId = requestAnimationFrame(tick);
+      }
+    };
+    rafId = requestAnimationFrame(tick);
+    return () => cancelAnimationFrame(rafId);
   }, [panelOpen]);
 
   // Scroll wheel navigation in month view