Find out the typical number of days between periods, what a normal period is, and what can cause irregular, long, or short menstrual cycles.

Subtraction is the easiest way to count days between two dates in Excel. You can use the arithmetic operator – (minus sign) to subtract one date from another to find the number of days between them.

How many days pass between periods can vary. Your cycle may have changed from 28 to 31 days because of changes in diet, exercise, hormones, or stress.