Find your ovulation day and fertile window from your last period. Plan or avoid pregnancy with a clear day-by-day calendar.
Estimated ovulation day
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Educational estimate only — not a contraceptive method. See a doctor for medical advice.
How ovulation is calculated
Ovulation usually happens about 14 days before your next period. This calculator subtracts 14 days from your expected next period date to estimate ovulation day. Your fertile window is the 5 days before ovulation plus ovulation day itself, because sperm can survive up to 5 days while the egg lives about 24 hours.
For better accuracy you can enter your last three cycle lengths — the calculator averages them. Remember this is an estimate: stress, illness and hormonal changes can shift ovulation. It should not be used as a sole method of contraception.
Frequently Asked Questions
When is my fertile window?
Your fertile window is the 5 days before ovulation plus ovulation day. Enter your last period date and cycle length above to see your exact fertile days highlighted on the calendar.
How accurate is an ovulation calculator?
It is a good estimate for women with regular cycles. Ovulation typically occurs 14 days before the next period, but stress or illness can shift it. For medical decisions, confirm with ovulation test strips or your doctor.
Can I get pregnant outside the fertile window?
Pregnancy is very unlikely outside the fertile window, because the egg survives only about 24 hours after ovulation. The highest chance is 2 days before ovulation and on ovulation day itself.