diff --git a/src/apple_eventkit_mcp/eventkit_store.py b/src/apple_eventkit_mcp/eventkit_store.py
index 89510a9..5b3985a 100644
--- a/src/apple_eventkit_mcp/eventkit_store.py
+++ b/src/apple_eventkit_mcp/eventkit_store.py
@@ -596,11 +596,21 @@ def _components_to_iso(self, components: NSDateComponents) -> Optional[str]:
             return None
 
     def _calendar_to_dict(self, calendar: EventKit.EKCalendar) -> dict:
-        """Convert EKCalendar to dictionary."""
+        """Convert EKCalendar to dictionary.
+
+        Includes the calendar's source (account) so callers can
+        disambiguate same-named calendars across accounts and route
+        by account (e.g. "all iCloud calendars" vs "all Google").
+        """
+        source = calendar.source()
         return {
             "id": calendar.calendarIdentifier(),
             "title": calendar.title(),
             "type": str(calendar.type()),
+            "source": {
+                "title": source.title() if source else None,
+                "type": str(source.sourceType()) if source else None,
+            },
             "allows_modifications": calendar.allowsContentModifications(),
         }
 
@@ -609,6 +619,8 @@ def _event_to_dict(self, event: EventKit.EKEvent) -> dict:
         notes = event.notes() or ""
         clean_notes, tags = decode_tags(notes)
 
+        cal = event.calendar()
+        cal_source = cal.source() if cal else None
         return {
             "id": event.calendarItemIdentifier(),
             "external_id": event.calendarItemExternalIdentifier(),
@@ -618,7 +630,8 @@ def _event_to_dict(self, event: EventKit.EKEvent) -> dict:
             "location": event.location(),
             "notes": clean_notes,
             "tags": tags,
-            "calendar": event.calendar().title() if event.calendar() else None,
+            "calendar": cal.title() if cal else None,
+            "calendar_source": cal_source.title() if cal_source else None,
             "is_all_day": event.isAllDay(),
             "url": str(event.URL()) if event.URL() else None,
             "has_recurrence": event.hasRecurrenceRules(),