diff --git a/resources/celerity/map.php b/resources/celerity/map.php
--- a/resources/celerity/map.php
+++ b/resources/celerity/map.php
@@ -122,7 +122,7 @@
     'rsrc/css/layout/phabricator-source-code-view.css' => '2ceee894',
     'rsrc/css/phui/calendar/phui-calendar-day.css' => '3b4a65d8',
     'rsrc/css/phui/calendar/phui-calendar-list.css' => '840baa8d',
-    'rsrc/css/phui/calendar/phui-calendar-month.css' => 'a6993b38',
+    'rsrc/css/phui/calendar/phui-calendar-month.css' => '5b213ea0',
     'rsrc/css/phui/calendar/phui-calendar.css' => '8345be98',
     'rsrc/css/phui/phui-action-header-view.css' => '89c497e7',
     'rsrc/css/phui/phui-action-list.css' => '4f4d09f2',
@@ -763,7 +763,7 @@
     'phui-calendar-css' => '8345be98',
     'phui-calendar-day-css' => '3b4a65d8',
     'phui-calendar-list-css' => '840baa8d',
-    'phui-calendar-month-css' => 'a6993b38',
+    'phui-calendar-month-css' => '5b213ea0',
     'phui-crumbs-view-css' => '594d719e',
     'phui-document-view-css' => '94d5dcd8',
     'phui-feed-story-css' => 'c9f3a0b5',
diff --git a/src/view/phui/calendar/PHUICalendarMonthView.php b/src/view/phui/calendar/PHUICalendarMonthView.php
--- a/src/view/phui/calendar/PHUICalendarMonthView.php
+++ b/src/view/phui/calendar/PHUICalendarMonthView.php
@@ -189,6 +189,7 @@
     $class = $event_list['class'];
     $date = $event_list['date'];
     $cell_day_secret_link = null;
+    $week_number = null;
 
     if ($date) {
       $uri = $event_list['uri'];
@@ -201,6 +202,16 @@
           'href' => $uri,
         ),
         $date->format('j'));
+
+      if ($date->format('w') == 1) {
+        $week_number = phutil_tag(
+          'a',
+          array(
+            'class' => 'phui-calendar-week-number',
+            'href' => $uri,
+          ),
+          $date->format('W'));
+      }
     } else {
       $cell_day = null;
     }
@@ -234,6 +245,7 @@
       ),
       array(
         $cell_day_secret_link,
+        $week_number,
         $cell_day,
         $today_slot,
       ));
diff --git a/webroot/rsrc/css/phui/calendar/phui-calendar-month.css b/webroot/rsrc/css/phui/calendar/phui-calendar-month.css
--- a/webroot/rsrc/css/phui/calendar/phui-calendar-month.css
+++ b/webroot/rsrc/css/phui/calendar/phui-calendar-month.css
@@ -94,6 +94,15 @@
   color: {$green};
 }
 
+table.phui-calendar-view a.phui-calendar-week-number {
+  color: {$lightgreyborder};
+  padding: 4px;
+  display: inline-block;
+  min-width: 16px;
+  text-align: center;
+  float: left;
+}
+
 table.phui-calendar-view a.phui-calendar-date-number {
   color: {$lightgreytext};
   padding: 4px;