Trying to conceive? Knowing your fertile window is one of the most powerful things you can do. This free ovulation calculator estimates your most fertile days, your ovulation date, and even your due date if you conceive this cycle — just enter the first day of your last period and your average cycle length.

This estimate assumes a typical 14-day luteal phase and is for general guidance only — not medical advice or contraception. Cycles vary; tracking ovulation signs or using ovulation tests improves accuracy.

How Ovulation Works

Ovulation — when an ovary releases an egg — typically happens about 14 days before your next period. Because sperm can survive up to 5 days and the egg lives about 24 hours, your fertile window spans roughly the 5 days before ovulation plus ovulation day itself. The 2–3 days leading up to ovulation are the most fertile.

This calculator uses a standard 14-day luteal phase and your cycle length to estimate these dates. Every body is different, so tracking ovulation signs (basal body temperature, cervical mucus) or using ovulation predictor kits can fine-tune your timing.

Frequently Asked Questions

When am I most fertile?

Your most fertile days are the 2–3 days leading up to and including ovulation. Because sperm can live several days, having intercourse in the days just before ovulation gives the best chance of conception.

How accurate is an ovulation calculator?

It provides a good estimate for those with regular cycles, but it’s based on averages. If your cycles are irregular, ovulation tests or tracking your basal body temperature and cervical mucus will give you more precise timing.

Can I use this as birth control?

No. This calculator is for planning conception only and should never be relied on to prevent pregnancy. Talk to your healthcare provider about effective contraception.