diff --git a/chrono/manager/views.py b/chrono/manager/views.py
index b095f9ed..f9cdbe68 100644
--- a/chrono/manager/views.py
+++ b/chrono/manager/views.py
@@ -1510,7 +1510,11 @@ class AgendaDayView(AgendaDateView, DayArchiveView):
         context['hours'] = [datetime.time(hour=i) for i in range(start_time.hour, end_time.hour)]
 
         def get_time_ratio(t1, t2):
-            return 100 * ((t1.hour - t2.hour) * 60 + t1.minute - t2.minute) // 60
+            return (
+                100
+                * ((t1.hour - t2.hour) * 60 + t1.minute - t2.minute)
+                // (end_time.hour * 60 + end_time.minute - (start_time.hour * 60 + start_time.minute))
+            )
 
         bookings = Booking.objects.filter(event__in=events)
         bookings_by_user = collections.defaultdict(list)