diff --git a/src/view/phui/calendar/PHUICalendarDayView.php b/src/view/phui/calendar/PHUICalendarDayView.php
index 69bdb69239..533fa0f446 100644
--- a/src/view/phui/calendar/PHUICalendarDayView.php
+++ b/src/view/phui/calendar/PHUICalendarDayView.php
@@ -1,390 +1,323 @@
 <?php
 
 final class PHUICalendarDayView extends AphrontView {
 
   private $day;
   private $month;
   private $year;
   private $browseURI;
   private $events = array();
 
   public function addEvent(AphrontCalendarDayEventView $event) {
     $this->events[] = $event;
     return $this;
   }
 
   public function setBrowseURI($browse_uri) {
     $this->browseURI = $browse_uri;
     return $this;
   }
   private function getBrowseURI() {
     return $this->browseURI;
   }
 
   public function __construct($year, $month, $day = null) {
     $this->day = $day;
     $this->month = $month;
     $this->year = $year;
   }
 
   public function render() {
     require_celerity_resource('phui-calendar-day-css');
 
     $hours = $this->getHoursOfDay();
     $hourly_events = array();
     $rows = array();
 
     // sort events into buckets by their start time
     // pretend no events overlap
     foreach ($hours as $hour) {
       $events = array();
       $hour_start = $hour->format('U');
       $hour_end = id(clone $hour)->modify('+1 hour')->format('U');
       foreach ($this->events as $event) {
         if ($event->getEpochStart() >= $hour_start
           && $event->getEpochStart() < $hour_end) {
           $events[] = $event;
         }
       }
       $count_events = count($events);
       $n = 0;
       foreach ($events as $event) {
         $event_start = $event->getEpochStart();
         $event_end = $event->getEpochEnd();
 
         $top = ((($event_start - $hour_start) / ($hour_end - $hour_start))
           * 100).'%';
         $height = ((($event_end - $event_start) / ($hour_end - $hour_start))
           * 100).'%';
 
         $hourly_events[$event->getEventID()] = array(
           'hour' => $hour,
           'event' => $event,
           'offset' => '0',
           'width' => '100%',
           'top' => $top,
           'height' => $height,
         );
 
         $n++;
       }
     }
 
     $clusters = $this->findClusters();
     foreach ($clusters as $cluster) {
       $hourly_events = $this->updateEventsFromCluster(
         $cluster,
         $hourly_events);
     }
 
     // actually construct table
     foreach ($hours as $hour) {
       $drawn_hourly_events = array();
       $cell_time = phutil_tag(
         'td',
         array('class' => 'phui-calendar-day-hour'),
         $hour->format('g A'));
 
       foreach ($hourly_events as $hourly_event) {
         if ($hourly_event['hour'] == $hour) {
           $drawn_hourly_events[] = $this->drawEvent(
             $hourly_event['event'],
             $hourly_event['offset'],
             $hourly_event['width'],
             $hourly_event['top'],
             $hourly_event['height']);
         }
       }
       $cell_event = phutil_tag(
         'td',
         array('class' => 'phui-calendar-day-events'),
         $drawn_hourly_events);
 
       $row = phutil_tag(
         'tr',
         array(),
         array($cell_time, $cell_event));
 
       $rows[] = $row;
     }
 
     $table = phutil_tag(
       'table',
       array('class' => 'phui-calendar-day-view'),
       array(
         '',
         $rows,
       ));
 
     $header = $this->renderDayViewHeader();
 
     $day_box = (new PHUIObjectBoxView())
       ->setHeader($header)
       ->appendChild($table);
 
     return $day_box;
   }
 
   private function renderDayViewHeader() {
     $button_bar = null;
 
     // check for a browseURI, which means we need "fancy" prev / next UI
     $uri = $this->getBrowseURI();
     if ($uri) {
       list($prev_year, $prev_month, $prev_day) = $this->getPrevDay();
       $prev_uri = $uri.$prev_year.'/'.$prev_month.'/'.$prev_day.'/';
 
       list($next_year, $next_month, $next_day) = $this->getNextDay();
       $next_uri = $uri.$next_year.'/'.$next_month.'/'.$next_day.'/';
 
       $button_bar = new PHUIButtonBarView();
 
       $left_icon = id(new PHUIIconView())
           ->setIconFont('fa-chevron-left bluegrey');
       $left = id(new PHUIButtonView())
         ->setTag('a')
         ->setColor(PHUIButtonView::GREY)
         ->setHref($prev_uri)
         ->setTitle(pht('Previous Day'))
         ->setIcon($left_icon);
 
       $right_icon = id(new PHUIIconView())
           ->setIconFont('fa-chevron-right bluegrey');
       $right = id(new PHUIButtonView())
         ->setTag('a')
         ->setColor(PHUIButtonView::GREY)
         ->setHref($next_uri)
         ->setTitle(pht('Next Day'))
         ->setIcon($right_icon);
 
       $button_bar->addButton($left);
       $button_bar->addButton($right);
 
     }
 
     $day_of_week = $this->getDayOfWeek();
     $header_text = $this->getDateTime()->format('F j, Y');
     $header_text = $day_of_week.', '.$header_text;
 
     $header = id(new PHUIHeaderView())
       ->setHeader($header_text);
 
     if ($button_bar) {
       $header->setButtonBar($button_bar);
     }
 
     return $header;
   }
 
   private function updateEventsFromCluster($cluster, $hourly_events) {
     $cluster_size = count($cluster);
 
     $n = 0;
     foreach ($cluster as $cluster_member) {
       $event_id = $cluster_member->getEventID();
       $offset = (($n / $cluster_size) * 100).'%';
       $width = ((1 / $cluster_size) * 100).'%';
 
       if (isset($hourly_events[$event_id])) {
         $hourly_events[$event_id]['offset'] = $offset;
         $hourly_events[$event_id]['width'] = $width;
       }
       $n++;
     }
 
     return $hourly_events;
   }
 
   private function drawEvent(
     AphrontCalendarDayEventView $event,
     $offset,
     $width,
     $top,
     $height) {
     $name = phutil_tag(
       'a',
       array(
         'class' => 'phui-calendar-day-event-link',
         'href' => $event->getURI(),
       ),
       $event->getName());
 
     $div = phutil_tag(
       'div',
       array(
         'class' => 'phui-calendar-day-event',
         'style' => 'left: '.$offset
           .'; width: '.$width
           .'; top: '.$top
           .'; height: '.$height
           .';',
       ),
       $name);
 
     return $div;
   }
 
   private function getDayOfWeek() {
     $date = $this->getDateTime();
     $day_of_week = $date->format('l');
     return $day_of_week;
   }
 
   // returns DateTime of each hour in the day
   private function getHoursOfDay() {
     $included_datetimes = array();
 
     $day_datetime = $this->getDateTime();
     $day_epoch = $day_datetime->format('U');
 
     $day_datetime->modify('+1 day');
     $next_day_epoch = $day_datetime->format('U');
 
     $included_time = $day_epoch;
     $included_datetime = $this->getDateTime();
 
     while ($included_time < $next_day_epoch) {
       $included_datetimes[] = clone $included_datetime;
 
       $included_datetime->modify('+1 hour');
       $included_time = $included_datetime->format('U');
     }
 
     return $included_datetimes;
   }
 
-  private function getNumberOfDaysInMonth($month, $year) {
-    $user = $this->user;
-    $timezone = new DateTimeZone($user->getTimezoneIdentifier());
-
-    list($next_year, $next_month) = $this->getNextYearAndMonth($month, $year);
-
-    $end_date = new DateTime("{$next_year}-{$next_month}-01", $timezone);
-    $end_epoch = $end_date->format('U');
-
-    $days = 0;
-    for ($day = 1; $day <= 31; $day++) {
-      $day_date = new DateTime("{$year}-{$month}-{$day}", $timezone);
-      $day_epoch = $day_date->format('U');
-      if ($day_epoch >= $end_epoch) {
-        break;
-      } else {
-        $days++;
-      }
-    }
-
-    return $days;
-  }
-
   private function getPrevDay() {
-    $day = $this->day;
-    $month = $this->month;
-    $year = $this->year;
-
-    $prev_year = $year;
-    $prev_month = $month;
-    $prev_day = $day - 1;
-    if ($prev_day == 0) {
-      $prev_month--;
-      if ($prev_month == 0) {
-        $prev_year--;
-        $prev_month = 12;
-      }
-      $prev_day = $this->getNumberOfDaysInMonth($prev_month, $prev_year);
-    }
-
-    return array($prev_year, $prev_month, $prev_day);
+    $prev = $this->getDateTime();
+    $prev->modify('-1 day');
+    return array(
+      $prev->format('Y'),
+      $prev->format('m'),
+      $prev->format('d'),
+    );
   }
 
   private function getNextDay() {
-    $day = $this->day;
-    $month = $this->month;
-    $year = $this->year;
-
-    $next_year = $year;
-    $next_month = $month;
-    $next_day = $day + 1;
-    $days_in_month = $this->getNumberOfDaysInMonth($month, $year);
-    if ($next_day > $days_in_month) {
-      $next_day = 1;
-      $next_month++;
-    }
-    if ($next_month == 13) {
-      $next_year++;
-      $next_month = 1;
-    }
-
-    return array($next_year, $next_month, $next_day);
-  }
-
-  private function getNextYearAndMonth($month, $year) {
-    $next_year = $year;
-    $next_month = $month + 1;
-    if ($next_month == 13) {
-      $next_year = $year + 1;
-      $next_month = 1;
-    }
-
-    return array($next_year, $next_month);
-  }
-
-  private function getPrevYearAndMonth($month, $year) {
-    $prev_year = $year;
-    $prev_month = $month - 1;
-    if ($prev_month == 0) {
-      $prev_year = $year - 1;
-      $prev_month = 12;
-    }
-
-    return array($prev_year, $prev_month);
+    $next = $this->getDateTime();
+    $next->modify('+1 day');
+    return array(
+      $next->format('Y'),
+      $next->format('m'),
+      $next->format('d'),
+    );
   }
 
   private function getDateTime() {
     $user = $this->user;
-
     $timezone = new DateTimeZone($user->getTimezoneIdentifier());
 
     $day = $this->day;
     $month = $this->month;
     $year = $this->year;
 
     $date = new DateTime("{$year}-{$month}-{$day} ", $timezone);
 
     return $date;
   }
 
   private function findClusters() {
     $events = msort($this->events, 'getEpochStart');
     $clusters = array();
 
 
     foreach ($events as $event) {
       $destination_cluster_key = null;
       $event_start = $event->getEpochStart();
       $event_end = $event->getEpochEnd();
 
       foreach ($clusters as $key => $cluster) {
         foreach ($cluster as $clustered_event) {
           $compare_event_start = $clustered_event->getEpochStart();
           $compare_event_end = $clustered_event->getEpochEnd();
 
           if ($event_start < $compare_event_end
             && $event_end > $compare_event_start) {
             $destination_cluster_key = $key;
             break;
           }
         }
       }
 
       if ($destination_cluster_key !== null) {
         $clusters[$destination_cluster_key][] = $event;
       } else {
         $next_cluster = array();
         $next_cluster[] = $event;
         $clusters[] = $next_cluster;
       }
     }
 
     return $clusters;
   }
 }
diff --git a/src/view/phui/calendar/PHUICalendarMonthView.php b/src/view/phui/calendar/PHUICalendarMonthView.php
index c4a7624a3d..089d98144c 100644
--- a/src/view/phui/calendar/PHUICalendarMonthView.php
+++ b/src/view/phui/calendar/PHUICalendarMonthView.php
@@ -1,316 +1,317 @@
 <?php
 
 final class PHUICalendarMonthView extends AphrontView {
 
   private $day;
   private $month;
   private $year;
   private $holidays = array();
   private $events   = array();
   private $browseURI;
   private $image;
   private $error;
 
   public function setBrowseURI($browse_uri) {
     $this->browseURI = $browse_uri;
     return $this;
   }
   private function getBrowseURI() {
     return $this->browseURI;
   }
 
   public function addEvent(AphrontCalendarEventView $event) {
     $this->events[] = $event;
     return $this;
   }
 
   public function setImage($uri) {
     $this->image = $uri;
     return $this;
   }
 
   public function setInfoView(PHUIInfoView $error) {
     $this->error = $error;
     return $this;
   }
 
   public function setHolidays(array $holidays) {
     assert_instances_of($holidays, 'PhabricatorCalendarHoliday');
     $this->holidays = mpull($holidays, null, 'getDay');
     return $this;
   }
 
   public function __construct($month, $year, $day = null) {
     $this->day = $day;
     $this->month = $month;
     $this->year = $year;
   }
 
   public function render() {
     if (empty($this->user)) {
       throw new Exception('Call setUser() before render()!');
     }
 
     $events = msort($this->events, 'getEpochStart');
 
     $days = $this->getDatesInMonth();
 
     require_celerity_resource('phui-calendar-month-css');
 
     $first = reset($days);
     $empty = $first->format('w');
 
     $markup = array();
 
     $empty_box = phutil_tag(
       'div',
       array('class' => 'phui-calendar-day phui-calendar-empty'),
       '');
 
     for ($ii = 0; $ii < $empty; $ii++) {
       $markup[] = $empty_box;
     }
 
     $show_events = array();
 
     foreach ($days as $day) {
       $day_number = $day->format('j');
 
       $holiday = idx($this->holidays, $day->format('Y-m-d'));
       $class = 'phui-calendar-day';
       $weekday = $day->format('w');
 
       if ($day_number == $this->day) {
         $class .= ' phui-calendar-today';
       }
 
       if ($holiday || $weekday == 0 || $weekday == 6) {
         $class .= ' phui-calendar-not-work-day';
       }
 
       $day->setTime(0, 0, 0);
       $epoch_start = $day->format('U');
 
       $day->modify('+1 day');
       $epoch_end = $day->format('U');
 
       if ($weekday == 0) {
         $show_events = array();
       } else {
         $show_events = array_fill_keys(
           array_keys($show_events),
           phutil_tag_div(
             'phui-calendar-event phui-calendar-event-empty',
             "\xC2\xA0")); // &nbsp;
       }
 
       $list_events = array();
       foreach ($events as $event) {
         if ($event->getEpochStart() >= $epoch_end) {
           // This list is sorted, so we can stop looking.
           break;
         }
         if ($event->getEpochStart() < $epoch_end &&
             $event->getEpochEnd() > $epoch_start) {
           $list_events[] = $event;
         }
       }
 
       $list = new PHUICalendarListView();
       $list->setUser($this->user);
       foreach ($list_events as $item) {
         $list->addEvent($item);
       }
 
       $holiday_markup = null;
       if ($holiday) {
         $name = $holiday->getName();
         $holiday_markup = phutil_tag(
           'div',
           array(
             'class' => 'phui-calendar-holiday',
             'title' => $name,
           ),
           $name);
       }
 
       $markup[] = phutil_tag_div(
         $class,
         array(
           phutil_tag_div('phui-calendar-date-number', $day_number),
           $holiday_markup,
           $list,
         ));
     }
 
     $table = array();
     $rows = array_chunk($markup, 7);
     foreach ($rows as $row) {
       $cells = array();
       while (count($row) < 7) {
         $row[] = $empty_box;
       }
       $j = 0;
       foreach ($row as $cell) {
         if ($j == 0) {
           $cells[] = phutil_tag(
             'td',
             array(
               'class' => 'phui-calendar-month-weekstart',
             ),
             $cell);
         } else {
           $cells[] = phutil_tag('td', array(), $cell);
         }
         $j++;
       }
       $table[] = phutil_tag('tr', array(), $cells);
     }
 
     $header = phutil_tag(
       'tr',
       array('class' => 'phui-calendar-day-of-week-header'),
       array(
         phutil_tag('th', array(), pht('Sun')),
         phutil_tag('th', array(), pht('Mon')),
         phutil_tag('th', array(), pht('Tue')),
         phutil_tag('th', array(), pht('Wed')),
         phutil_tag('th', array(), pht('Thu')),
         phutil_tag('th', array(), pht('Fri')),
         phutil_tag('th', array(), pht('Sat')),
       ));
 
     $table = phutil_tag(
       'table',
       array('class' => 'phui-calendar-view'),
       array(
         $header,
         phutil_implode_html("\n", $table),
       ));
 
     $box = id(new PHUIObjectBoxView())
       ->setHeader($this->renderCalendarHeader($first))
       ->appendChild($table);
     if ($this->error) {
       $box->setInfoView($this->error);
 
     }
 
     return $box;
   }
 
   private function renderCalendarHeader(DateTime $date) {
     $button_bar = null;
 
     // check for a browseURI, which means we need "fancy" prev / next UI
     $uri = $this->getBrowseURI();
     if ($uri) {
       list($prev_year, $prev_month) = $this->getPrevYearAndMonth();
       $prev_uri = $uri.$prev_year.'/'.$prev_month.'/';
 
       list($next_year, $next_month) = $this->getNextYearAndMonth();
       $next_uri = $uri.$next_year.'/'.$next_month.'/';
 
       $button_bar = new PHUIButtonBarView();
 
       $left_icon = id(new PHUIIconView())
           ->setIconFont('fa-chevron-left bluegrey');
       $left = id(new PHUIButtonView())
         ->setTag('a')
         ->setColor(PHUIButtonView::GREY)
         ->setHref($prev_uri)
         ->setTitle(pht('Previous Month'))
         ->setIcon($left_icon);
 
       $right_icon = id(new PHUIIconView())
           ->setIconFont('fa-chevron-right bluegrey');
       $right = id(new PHUIButtonView())
         ->setTag('a')
         ->setColor(PHUIButtonView::GREY)
         ->setHref($next_uri)
         ->setTitle(pht('Next Month'))
         ->setIcon($right_icon);
 
       $button_bar->addButton($left);
       $button_bar->addButton($right);
 
     }
 
     $header = id(new PHUIHeaderView())
       ->setHeader($date->format('F Y'));
 
     if ($button_bar) {
       $header->setButtonBar($button_bar);
     }
 
     if ($this->image) {
       $header->setImage($this->image);
     }
 
     return $header;
   }
 
   private function getNextYearAndMonth() {
-    $month = $this->month;
-    $year = $this->year;
-
-    $next_year = $year;
-    $next_month = $month + 1;
-    if ($next_month == 13) {
-      $next_year = $year + 1;
-      $next_month = 1;
-    }
-
-    return array($next_year, $next_month);
+    $next = $this->getDateTime();
+    $next->modify('+1 month');
+    return array(
+      $next->format('Y'),
+      $next->format('m'),
+    );
   }
 
   private function getPrevYearAndMonth() {
-    $month = $this->month;
-    $year = $this->year;
-
-    $prev_year = $year;
-    $prev_month = $month - 1;
-    if ($prev_month == 0) {
-      $prev_year = $year - 1;
-      $prev_month = 12;
-    }
-
-    return array($prev_year, $prev_month);
+    $prev = $this->getDateTime();
+    $prev->modify('-1 month');
+    return array(
+      $prev->format('Y'),
+      $prev->format('m'),
+    );
   }
 
   /**
    * Return a DateTime object representing the first moment in each day in the
    * month, according to the user's locale.
    *
    * @return list List of DateTimes, one for each day.
    */
   private function getDatesInMonth() {
     $user = $this->user;
 
     $timezone = new DateTimeZone($user->getTimezoneIdentifier());
 
     $month = $this->month;
     $year = $this->year;
 
     // Get the year and month numbers of the following month, so we can
     // determine when this month ends.
     list($next_year, $next_month) = $this->getNextYearAndMonth();
 
     $end_date = new DateTime("{$next_year}-{$next_month}-01", $timezone);
     $end_epoch = $end_date->format('U');
 
     $days = array();
     for ($day = 1; $day <= 31; $day++) {
       $day_date = new DateTime("{$year}-{$month}-{$day}", $timezone);
       $day_epoch = $day_date->format('U');
       if ($day_epoch >= $end_epoch) {
         break;
       } else {
         $days[] = $day_date;
       }
     }
 
     return $days;
   }
 
+  private function getDateTime() {
+    $user = $this->user;
+    $timezone = new DateTimeZone($user->getTimezoneIdentifier());
+
+    $month = $this->month;
+    $year = $this->year;
+
+    $date = new DateTime("{$year}-{$month}-01 ", $timezone);
+
+    return $date;
+  }
 }