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
@@ -586,6 +586,9 @@
       $min_date = $start->newPHPDateTime();
       $max_date = $end->newPHPDateTime();
 
+      // Subtract one second since the stored date is exclusive.
+      $max_date = $max_date->modify('-1 second');
+
       $min_day = $min_date->format('Y m d');
       $max_day = $max_date->format('Y m d');
 
@@ -842,7 +845,11 @@
     // 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 ($this->getIsAllDay()) {
+
+    // For imported events, the end date is already stored with this
+    // adjustment.
+
+    if ($this->getIsAllDay() && !$this->isImportedEvent()) {
       $datetime = $datetime
         ->newAbsoluteDateTime()
         ->setHour(0)
diff --git a/src/view/phui/calendar/PHUICalendarListView.php b/src/view/phui/calendar/PHUICalendarListView.php
--- a/src/view/phui/calendar/PHUICalendarListView.php
+++ b/src/view/phui/calendar/PHUICalendarListView.php
@@ -198,8 +198,11 @@
       $viewer,
       $event->getEpochEnd()));
 
+    $end_date = $end->getDateTime();
+    $end_date = $end_date->modify('-1 second');
+
     $start_date = $start->getDateTime()->format('m d Y');
-    $end_date = $end->getDateTime()->format('m d Y');
+    $end_date = $end_date->format('m d Y');
 
     if ($event->getIsAllDay()) {
       if ($start_date == $end_date) {