Period & cycle calculators
Every tool is free, private and runs entirely in your browser.
Period Calculator
Free period calculator: predict your next period, ovulation day and fertile window in seconds. Private — everything is calculated in your browser.
Irregular Periods
Irregular cycles? This period calculator predicts date ranges from your shortest and longest cycles, with ovulation and fertile windows included. Free and private.
Late Period
Find out exactly how many days late your period is, common reasons why, and what to do next. Free, private, no sign-up — results update as you type.
Next Period
When is my next period? Enter your last period date and cycle length to get an instant next-period date plus a 6-month forecast. Free, private, no sign-up.
This tool provides estimates for personal planning only and is not a substitute for professional medical advice, diagnosis or treatment. Predictions must not be used as contraception. If you have concerns about your cycle, heavy bleeding, severe pain or missed periods, please consult a licensed clinician.