How to Calculate Your Menstrual Cycle
Your menstrual cycle is counted from day one of your period to day one of the next. Here's how to calculate it correctly.
Step 1: Mark day one
Day one is the first day of full menstrual flow — not spotting. Track this in a calendar or cycle app.
Step 2: Count to the next day one
The number of days between day one of one period and day one of the next is your cycle length. A typical range is 21–35 days; the average is 28.
Step 3: Identify your phases
Follicular phase: day 1 through ovulation. Ovulation: roughly 14 days before your next period. Luteal phase: ovulation through the day before your next period (typically 12–14 days).