diff --git a/admin/intro.php b/admin/intro.php
index c3219a92c..42a0ba543 100644
--- a/admin/intro.php
+++ b/admin/intro.php
@@ -220,6 +220,8 @@ $date_string = $date->format('Y-m-d');
 
 if (!isset($_SESSION['cache_activity_last_weeks']) or $_SESSION['cache_activity_last_weeks']['calculated_on'] < strtotime('5 minutes ago'))
 {
+  $start_time = get_moment();
+
   $query = '
   SELECT
       DATE_FORMAT(occured_on , \'%Y-%m-%d\') AS activity_day,
@@ -251,6 +253,8 @@ if (!isset($_SESSION['cache_activity_last_weeks']) or $_SESSION['cache_activity_
     @$activity_last_weeks[$week][$day_nb]['date'] = format_date($day_date->getTimestamp());
   }
 
+  $logger->debug('[admin/intro::'.__LINE__.'] recent activity calculated in '.get_elapsed_time($start_time, get_moment()));
+
   $_SESSION['cache_activity_last_weeks'] = array(
     'calculated_on' => time(),
     'data' => $activity_last_weeks,