diff --git a/event/static/js/calendar.js b/event/static/js/calendar.js
index a94db4d..9256c3b 100644
--- a/event/static/js/calendar.js
+++ b/event/static/js/calendar.js
@@ -1,7 +1,10 @@
 // Based on https://stackoverflow.com/a/15289883
 function computeDateDifferenceInHours (date1, date2) {
+  d1 = new Date(date1.getYear(), date1.getMonth(), date1.getDate(), date1.getHours());
+  d2 = new Date(date2.getYear(), date2.getMonth(), date2.getDate(), date2.getHours());
+
   const msPerHour = 60 * 60 * 1000;
-  return Math.floor(Math.abs(date2.getTime() - date1.getTime()) / msPerHour);
+  return Math.abs(d2.getTime() - d1.getTime()) / msPerHour;
 }
 
 
@@ -87,7 +90,8 @@ class Calendar {
     this.startHourToDisplay = this.startDate.getHours();
     this.endHourToDisplay = this.endDate.getHours();
 
-    this.nbHoursToDisplay = computeDateDifferenceInHours(this.startDate, this.endDate);
+    this.nbHoursToDisplay = Math.floor(computeDateDifferenceInHours(this.startDate, this.endDate));
+  }
   }
 
 
@@ -484,7 +488,7 @@ class Event {
       return 1;
     }
 
-    return 1 + computeDateDifferenceInHours(this.calendar.startDate, this.startDate);
+    return 1 + Math.floor(computeDateDifferenceInHours(this.calendar.startDate, this.startDate));
   }
 
   // Assuming the events can appear in the calendar
@@ -493,8 +497,10 @@ class Event {
       return 1 + this.calendar.nbHoursToDisplay;
     }
 
+    let shiftedEndDate = new Date(this.endDate.getTime() + 1000 * 60 * 59);
+
     return 1 + this.calendar.nbHoursToDisplay
-             - computeDateDifferenceInHours(this.endDate, this.calendar.endDate);
+             - Math.ceil(computeDateDifferenceInHours(shiftedEndDate, this.calendar.endDate));
   }
 
   updatePositionInGrid () {