diff --git a/src/applications/calendar/editor/PhabricatorCalendarEventEditEngine.php b/src/applications/calendar/editor/PhabricatorCalendarEventEditEngine.php
--- a/src/applications/calendar/editor/PhabricatorCalendarEventEditEngine.php
+++ b/src/applications/calendar/editor/PhabricatorCalendarEventEditEngine.php
@@ -119,7 +119,7 @@
         ->setDescription(pht('End time of the event.'))
         ->setConduitDescription(pht('Change the end time of the event.'))
         ->setConduitTypeDescription(pht('New event end time.'))
-        ->setValue($object->getEndDateTimeEpoch()),
+        ->setValue($object->newEndDateTimeForEdit()->getEpoch()),
       id(new PhabricatorBoolEditField())
         ->setKey('cancelled')
         ->setOptions(pht('Active'), pht('Cancelled'))
diff --git a/src/applications/calendar/storage/PhabricatorCalendarEvent.php b/src/applications/calendar/storage/PhabricatorCalendarEvent.php
--- a/src/applications/calendar/storage/PhabricatorCalendarEvent.php
+++ b/src/applications/calendar/storage/PhabricatorCalendarEvent.php
@@ -857,7 +857,7 @@
     return $this->newStartDateTime()->getEpoch();
   }
 
-  public function newEndDateTime() {
+  public function newEndDateTimeForEdit() {
     $datetime = $this->getParameter('endDateTime');
     if ($datetime) {
       return $this->newDateTimeFromDictionary($datetime);
@@ -867,6 +867,25 @@
     return $this->newDateTimeFromEpoch($epoch);
   }
 
+  public function newEndDateTime() {
+    $datetime = $this->newEndDateTimeForEdit();
+
+    // If this is an all day event, we move the end date time forward to the
+    // first second of the following day. This is consistent with what users
+    // expect: an all day event from "Nov 1" to "Nov 1" lasts the entire day.
+    if ($this->getIsAllDay()) {
+      $datetime = $datetime
+        ->newAbsoluteDateTime()
+        ->setHour(0)
+        ->setMinute(0)
+        ->setSecond(0)
+        ->newRelativeDateTime('P1D')
+        ->newAbsoluteDateTime();
+    }
+
+    return $datetime;
+  }
+
   public function getEndDateTimeEpoch() {
     return $this->newEndDateTime()->getEpoch();
   }
diff --git a/src/applications/calendar/xaction/PhabricatorCalendarEventEndDateTransaction.php b/src/applications/calendar/xaction/PhabricatorCalendarEventEndDateTransaction.php
--- a/src/applications/calendar/xaction/PhabricatorCalendarEventEndDateTransaction.php
+++ b/src/applications/calendar/xaction/PhabricatorCalendarEventEndDateTransaction.php
@@ -7,7 +7,7 @@
 
   public function generateOldValue($object) {
     // TODO: Upgrade this.
-    return $object->getEndDateTimeEpoch();
+    return $object->newEndDateTimeForEdit()->getEpoch();
   }
 
   public function applyInternalEffects($object, $value) {