diff --git a/src/applications/calendar/controller/PhabricatorCalendarEventEditController.php b/src/applications/calendar/controller/PhabricatorCalendarEventEditController.php
index 38d12b099b..967c7deb19 100644
--- a/src/applications/calendar/controller/PhabricatorCalendarEventEditController.php
+++ b/src/applications/calendar/controller/PhabricatorCalendarEventEditController.php
@@ -74,6 +74,7 @@ final class PhabricatorCalendarEventEditController
     $name = $event->getName();
     $description = $event->getDescription();
     $type = $event->getStatus();
+    $is_all_day = $event->getIsAllDay();
 
     $current_policies = id(new PhabricatorPolicyQuery())
       ->setViewer($user)
@@ -95,6 +96,7 @@ final class PhabricatorCalendarEventEditController
       $subscribers = $request->getArr('subscribers');
       $edit_policy = $request->getStr('editPolicy');
       $view_policy = $request->getStr('viewPolicy');
+      $is_all_day = $request->getStr('isAllDay');
 
       $invitees = $request->getArr('invitees');
       $new_invitees = $this->getNewInviteeList($invitees, $event);
@@ -111,6 +113,11 @@ final class PhabricatorCalendarEventEditController
           PhabricatorCalendarEventTransaction::TYPE_NAME)
         ->setNewValue($name);
 
+      $xactions[] = id(new PhabricatorCalendarEventTransaction())
+        ->setTransactionType(
+          PhabricatorCalendarEventTransaction::TYPE_ALL_DAY)
+        ->setNewValue($is_all_day);
+
       $xactions[] = id(new PhabricatorCalendarEventTransaction())
         ->setTransactionType(
           PhabricatorCalendarEventTransaction::TYPE_START_DATE)
@@ -184,6 +191,13 @@ final class PhabricatorCalendarEventEditController
       ->setValue($type)
       ->setOptions($event->getStatusOptions());
 
+    $all_day_select = id(new AphrontFormCheckboxControl())
+      ->addCheckbox(
+        'isAllDay',
+        1,
+        pht('All Day Event'),
+        $is_all_day);
+
     $start_control = id(new AphrontFormDateControl())
       ->setUser($user)
       ->setName('start')
@@ -234,6 +248,7 @@ final class PhabricatorCalendarEventEditController
       ->setUser($user)
       ->appendChild($name)
       ->appendChild($status_select)
+      ->appendChild($all_day_select)
       ->appendChild($start_control)
       ->appendChild($end_control)
       ->appendControl($view_policies)
diff --git a/src/applications/calendar/editor/PhabricatorCalendarEventEditor.php b/src/applications/calendar/editor/PhabricatorCalendarEventEditor.php
index f00ba4349f..8c992ce16f 100644
--- a/src/applications/calendar/editor/PhabricatorCalendarEventEditor.php
+++ b/src/applications/calendar/editor/PhabricatorCalendarEventEditor.php
@@ -183,6 +183,16 @@ final class PhabricatorCalendarEventEditor
     return parent::applyCustomExternalTransaction($object, $xaction);
   }
 
+  protected function didApplyInternalEffects(
+    PhabricatorLiskDAO $object,
+    array $xactions) {
+
+    $object->removeViewerTimezone($this->requireActor());
+
+    return $xactions;
+  }
+
+
   protected function validateAllTransactions(
     PhabricatorLiskDAO $object,
     array $xactions) {
diff --git a/src/applications/calendar/query/PhabricatorCalendarEventQuery.php b/src/applications/calendar/query/PhabricatorCalendarEventQuery.php
index 1fd294781f..c66e367793 100644
--- a/src/applications/calendar/query/PhabricatorCalendarEventQuery.php
+++ b/src/applications/calendar/query/PhabricatorCalendarEventQuery.php
@@ -56,7 +56,13 @@ final class PhabricatorCalendarEventQuery
       $this->buildOrderClause($conn_r),
       $this->buildLimitClause($conn_r));
 
-    return $table->loadAllFromArray($data);
+    $events = $table->loadAllFromArray($data);
+
+    foreach ($events as $event) {
+      $event->applyViewerTimezone($this->getViewer());
+    }
+
+    return $events;
   }
 
   protected function buildJoinClauseParts(AphrontDatabaseConnection $conn_r) {
diff --git a/src/applications/calendar/storage/PhabricatorCalendarEvent.php b/src/applications/calendar/storage/PhabricatorCalendarEvent.php
index a63c869808..5d4d3cdd5a 100644
--- a/src/applications/calendar/storage/PhabricatorCalendarEvent.php
+++ b/src/applications/calendar/storage/PhabricatorCalendarEvent.php
@@ -24,6 +24,7 @@ final class PhabricatorCalendarEvent extends PhabricatorCalendarDAO
   protected $editPolicy;
 
   private $invitees = self::ATTACHABLE;
+  private $appliedViewer;
 
   const STATUS_AWAY = 1;
   const STATUS_SPORADIC = 2;
@@ -37,15 +38,112 @@ final class PhabricatorCalendarEvent extends PhabricatorCalendarDAO
     return id(new PhabricatorCalendarEvent())
       ->setUserPHID($actor->getPHID())
       ->setIsCancelled(0)
+      ->setIsAllDay(0)
       ->setViewPolicy($actor->getPHID())
       ->setEditPolicy($actor->getPHID())
-      ->attachInvitees(array());
+      ->attachInvitees(array())
+      ->applyViewerTimezone($actor);
+  }
+
+  public function applyViewerTimezone(PhabricatorUser $viewer) {
+    if ($this->appliedViewer) {
+      throw new Exception(pht('Viewer timezone is already applied!'));
+    }
+
+    $this->appliedViewer = $viewer;
+
+    if (!$this->getIsAllDay()) {
+      return $this;
+    }
+
+    $zone = $viewer->getTimeZone();
+
+
+    $this->setDateFrom(
+      $this->getDateEpochForTimeZone(
+        $this->getDateFrom(),
+        new DateTimeZone('GMT+12'),
+        'Y-m-d',
+        null,
+        $zone));
+
+    $this->setDateTo(
+      $this->getDateEpochForTimeZone(
+        $this->getDateTo(),
+        new DateTimeZone('GMT-12'),
+        'Y-m-d 23:59:59',
+        '-1 day',
+        $zone));
+
+    return $this;
+  }
+
+
+  public function removeViewerTimezone(PhabricatorUser $viewer) {
+    if (!$this->appliedViewer) {
+      throw new Exception(pht('Viewer timezone is not applied!'));
+    }
+
+    if ($viewer->getPHID() != $this->appliedViewer->getPHID()) {
+      throw new Exception(pht('Removed viewer must match applied viewer!'));
+    }
+
+    $this->appliedViewer = null;
+
+    if (!$this->getIsAllDay()) {
+      return $this;
+    }
+
+    $zone = $viewer->getTimeZone();
+
+    $this->setDateFrom(
+      $this->getDateEpochForTimeZone(
+        $this->getDateFrom(),
+        $zone,
+        'Y-m-d',
+        null,
+        new DateTimeZone('GMT+12')));
+
+    $this->setDateTo(
+      $this->getDateEpochForTimeZone(
+        $this->getDateTo(),
+        $zone,
+        'Y-m-d',
+        '+1 day',
+        new DateTimeZone('GMT-12')));
+
+    return $this;
+  }
+
+  private function getDateEpochForTimeZone(
+    $epoch,
+    $src_zone,
+    $format,
+    $adjust,
+    $dst_zone) {
+
+    $src = new DateTime('@'.$epoch);
+    $src->setTimeZone($src_zone);
+
+    if (strlen($adjust)) {
+      $adjust = ' '.$adjust;
+    }
+
+    $dst = new DateTime($src->format($format).$adjust, $dst_zone);
+    return $dst->format('U');
   }
 
   public function save() {
+    if ($this->appliedViewer) {
+      throw new Exception(
+        pht(
+          'Can not save event with viewer timezone still applied!'));
+    }
+
     if (!$this->mailKey) {
       $this->mailKey = Filesystem::readRandomCharacters(20);
     }
+
     return parent::save();
   }
 
diff --git a/src/applications/people/storage/PhabricatorUser.php b/src/applications/people/storage/PhabricatorUser.php
index ea138042b2..a6c9f6f349 100644
--- a/src/applications/people/storage/PhabricatorUser.php
+++ b/src/applications/people/storage/PhabricatorUser.php
@@ -682,6 +682,10 @@ EOBODY;
     }
   }
 
+  public function getTimeZone() {
+    return new DateTimeZone($this->getTimezoneIdentifier());
+  }
+
   public function __toString() {
     return $this->getUsername();
   }
diff --git a/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php b/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php
index c28fb135ee..1e75bd0432 100644
--- a/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php
+++ b/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php
@@ -569,6 +569,11 @@ abstract class PhabricatorApplicationTransactionEditor
     return $xaction;
   }
 
+  protected function didApplyInternalEffects(
+    PhabricatorLiskDAO $object,
+    array $xactions) {
+    return $xactions;
+  }
 
   protected function applyFinalEffects(
     PhabricatorLiskDAO $object,
@@ -731,6 +736,8 @@ abstract class PhabricatorApplicationTransactionEditor
         $this->applyInternalEffects($object, $xaction);
       }
 
+      $xactions = $this->didApplyInternalEffects($object, $xactions);
+
       $object->save();
 
       foreach ($xactions as $xaction) {