Period Calculator

Use this tool to calculate your most likely ovulation day and your fertile window. Results are shown on the calendar.

First Day of Your Last Period:

Pick the first day of your last menstrual period.

How long did it last (days)?

Average duration of your period.

Average Length of Cycles (days):

From the start of one period to the next.

Period (pink background) → Indicates your period days.

Fertile Window (light blue background) → Your most fertile days (from 4 days before to 1 day after ovulation).

Ovulation (blue event) → The day you're most likely to ovulate.