How is ovulation estimated?

Next period: ${fmt(next)} (expected bleeding ${fmt(next)}–${fmt(add(next,period-1))})
Ovulation: around ${fmt(ovu)}
Fertile window: ${fmt(fertStart)}–${fmt(fertEnd)}
PMS / prep window: around ${fmt(test)} onward

This calculator estimates ovulation about 14 days before the next predicted period.

Can this be used as contraception?

No. It is an educational estimate and should not be used as contraception or medical advice.

No. The static calculator runs in your browser.

Free cycle calculator

Estimate your next period, ovulation day and fertile window from your last period and average cycle length.

First day of last periodAverage cycle length (days)Typical period length (days)

Your cycle estimate will appear here.

This is educational and not medical advice or contraception. Download Cyca for private cycle tracking on iPhone.