Fixed #24980 -- Fixed day determination in admin calendar widget.

django/contrib/admin/static/admin/js/core.js

@@ -240,7 +240,10 @@ function findPosY(obj) {
             }
             ++i;
         }
-        return new Date(year, month, day);
+        // Create Date object from UTC since the parsed value is supposed to be
+        // in UTC, not local time. Also, the calendar uses UTC functions for
+        // date extraction.
+        return new Date(Date.UTC(year, month, day));
     };
 
 })();