How this ovulation calculator works
This ovulation calculator uses the same cycle data as our main period calculator: the first day of your last period, your average cycle length, and period length. Ovulation is estimated 14 days before your next predicted period, with a fertile window spanning five days before ovulation through one day after.
Why ovulation timing matters
Whether you're trying to conceive or simply want to understand your body better, knowing your fertile window helps you plan. Ovulation can shift from cycle to cycle, so treat this as a helpful estimate rather than a precise clock.
Frequently asked questions
How is ovulation day calculated?+
Ovulation typically happens about 14 days before your next period starts, regardless of your total cycle length. This calculator works backward from your predicted next period to estimate that day.
What is the fertile window?+
The fertile window is roughly five days before ovulation through one day after — the span of days when pregnancy is most possible, since sperm can survive for several days and the egg is viable for about 24 hours.
Can I use this to get pregnant or avoid pregnancy?+
It can help you understand your likely fertile days, but ovulation timing varies and this tool is an estimate, not a guarantee. It should never be relied on as a method of contraception.