Since an average year has an odd number of days, the number of weekdays shifts when comparing the same month year over year: A month that starts on a Friday and has five Saturdays one year will in the following year start on a Saturday and have five Sundays, and so forth. So, in effect, this hypothetical month dropped a Friday and added a Sunday.

Since room demand is not equal across weekdays, this shift can impact monthly key performance indicators materially.