Ovulation Calculator

How ovulation timing works

Ovulation is when an ovary releases an egg, and it's the most fertile point of your cycle. It happens about 14 days before your next period starts, regardless of how long your cycle is — the second half of the cycle (the luteal phase) stays fairly constant at around 14 days, while the first half varies. This calculator counts forward to your next period from the date you enter, then steps back 14 days to estimate ovulation.

Your fertile window

You can conceive on more than just ovulation day. Sperm can survive in the body for up to about five days, and the egg lives for roughly 24 hours after release. That makes the fertile window the five days leading up to ovulation plus ovulation day itself — the days when trying to conceive is most likely to succeed. The calculator highlights this window.

How to use it

• First day of your last period — the day bleeding started, not when it ended.
• Average cycle length — count from the first day of one period to the first day of the next. Twenty-eight days is typical, but anywhere from 21 to 35 is common.

How accurate is this?

It's an estimate based on cycle averages. Real ovulation can shift with stress, illness, and natural variation, especially if your cycles are irregular. For higher accuracy, combine the estimate with ovulation predictor kits, basal body temperature tracking, or cervical-mucus changes.

FAQ

Can I use this for birth control?

No. Calendar estimates are not a reliable form of contraception on their own — ovulation timing varies too much. Use a proven contraceptive method if you're trying to avoid pregnancy.

What if my cycles are irregular?

The prediction is less reliable with irregular cycles. Track several cycles to find your average, and consider physical fertility signs or a doctor's guidance for a clearer picture.

Does a longer cycle move ovulation later?

Yes. Because ovulation is counted back from the next period, a longer cycle pushes both the next period and the estimated ovulation date later, while keeping the ~14-day luteal phase the same.