How is ovulation estimated?

Ovulation is estimated as roughly 14 days before your next predicted period, because the luteal phase after ovulation is fairly consistent at about 14 days. The fertile window covers the 5 days before ovulation through the day itself.

Can I rely on this for contraception?

No. Cycle-based predictions are estimates only and cycles vary month to month. Do not use this tool as a contraceptive method or a replacement for medical advice.

Is my data saved anywhere?

No. Every calculation runs in your browser and nothing is uploaded, stored or shared.

Period & Cycle Tracker

Predict your next period, ovulation and fertile window.

Period & cycle tracker

Enter the first day of your last period and your usual cycle length to see your next period date, estimated ovulation day and fertile window.

The estimate assumes a roughly 14-day luteal phase, so ovulation is placed about two weeks before your next expected period. Cycles vary naturally — treat these as predictions, not guarantees. Everything is calculated privately in your browser.