diff --git a/package.json b/package.json
index 58c071d..f55d526 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "my-weekly-todo-list",
-  "version": "1.71.2",
+  "version": "1.71.3",
   "description": "A web-based weekly task management application that organizes to-dos and calendar events in a single, intuitive weekly view",
   "main": "index.js",
   "scripts": {
diff --git a/src/lib/outlook-calendar.ts b/src/lib/outlook-calendar.ts
index ffe703a..cd802d2 100644
--- a/src/lib/outlook-calendar.ts
+++ b/src/lib/outlook-calendar.ts
@@ -272,6 +272,17 @@ const ensureTimeZone = (dateTimeObj: any) => {
 /**
  * Create Outlook Event
  */
+// Normalize Outlook response dateTime: ensure UTC dates have Z suffix
+const normalizeOutlookDateTime = (dtObj: any) => {
+    if (!dtObj?.dateTime) return dtObj;
+    let dt = dtObj.dateTime;
+    // Outlook returns UTC datetimes without Z suffix — append it
+    if (dt && typeof dt === 'string' && dtObj.timeZone === 'UTC' && !dt.endsWith('Z')) {
+        dt = dt + 'Z';
+    }
+    return { dateTime: dt, timeZone: dtObj.timeZone };
+};
+
 export const createEvent = async (
     accessToken: string,
     calendarId: string,
@@ -281,7 +292,8 @@ export const createEvent = async (
         method: 'POST',
         headers: {
             'Authorization': `Bearer ${accessToken}`,
-            'Content-Type': 'application/json'
+            'Content-Type': 'application/json',
+            'Prefer': 'outlook.timezone="UTC"'
         },
         body: JSON.stringify({
             subject: event.summary,
@@ -325,8 +337,8 @@ export const createEvent = async (
         id: created.id,
         summary: created.subject,
         description: created.bodyPreview,
-        start: created.start,
-        end: created.end,
+        start: normalizeOutlookDateTime(created.start),
+        end: normalizeOutlookDateTime(created.end),
         location: created.location?.displayName,
         allDay: created.isAllDay
     };
@@ -372,9 +384,10 @@ export const updateEvent = async (
         } : {}),
     });
 
-    const patchHeaders = {
+    const patchHeaders: Record<string, string> = {
         'Authorization': `Bearer ${accessToken}`,
-        'Content-Type': 'application/json'
+        'Content-Type': 'application/json',
+        'Prefer': 'outlook.timezone="UTC"'
     };
 
     const encodedEventId = encodeURIComponent(eventId);
@@ -402,8 +415,8 @@ export const updateEvent = async (
         id: updated.id,
         summary: updated.subject,
         description: updated.bodyPreview,
-        start: updated.start,
-        end: updated.end,
+        start: normalizeOutlookDateTime(updated.start),
+        end: normalizeOutlookDateTime(updated.end),
         location: updated.location?.displayName,
         allDay: updated.isAllDay
     };