How is ovulation estimated?

For a regular cycle, ovulation is estimated as cycle length minus 14 days from the first day of your last period. Your fertile window includes the five days before and the day of ovulation.

Is this a form of contraception?

No. This calculator estimates when you may be most fertile — it is not reliable for preventing pregnancy. If you're trying to avoid pregnancy, use a proven method and speak with a clinician.

What if my cycle is irregular?

Irregular cycles make ovulation harder to predict. Ovulation predictor kits, basal body temperature tracking or a fertility specialist can give a more personal picture.

Ovulation Calculator

Estimate your fertile window and ovulation day. Private and instant — no account required.

First day of your last period

Average cycle length28 days

Estimated ovulation

Friday, September 4, 2026

Fertile window: Aug 30 – Sep 4, 2026

Next period expected: Sep 18, 2026

This calculator estimates your most fertile days — it is not a form of contraception. If you're trying to avoid pregnancy, please use a proven method.

September 2026

Highlighted: fertile window. Filled: estimated ovulation day.

Su	Mo	Tu	We	Th	Fr	Sa

Ovulation Calculator

Frequently asked questions

How is ovulation estimated?

Is this a form of contraception?

What if my cycle is irregular?