Ovulation Calculator

The ovulation calculator finds the most likely ovulation day and the fertile window — the days when the chance of getting pregnant is highest. Enter the first day of your last period and your cycle length: the calculator shows the ovulation date, fertile days, best days to conceive and the next period date, and builds a three-month cycle calendar below. The calculation is instant, on your device.

How to use the calculator

Step one — enter the first day of your last period (the first, not the last — the cycle counts from it). Step two — enter the cycle length in days: from the first day of one period to the first day of the next. If your cycle is irregular, use the average of the last 3–6 cycles. The calculator instantly shows the expected ovulation date, fertile window and a color-coded cycle calendar.

How ovulation is calculated

The luteal phase — from ovulation to the next period — lasts 13–15 days for most women and is fairly stable. So ovulation is calculated as: ovulation = first day of last period + cycle length − 14 days. Example: a 28-day cycle starting on the 5th — ovulation around the 19th. The fertile window is five days before ovulation and one day after: sperm can fertilize for up to five days, the egg lives about a day.

Best days to conceive

The chance of conception is highest two days before ovulation and on the day itself — the calculator lists them separately. Regular intercourse every other day during the fertile window covers the whole period. Remember: ovulation can shift with stress, illness, travel and medication.

Not a contraception method

The calendar method is an unreliable contraception: sperm live up to five days and ovulation can shift by almost a week. To prevent pregnancy use modern contraceptives; for exact ovulation timing use ovulation tests, basal temperature tracking or ultrasound. This calculator gives an estimate and does not replace a gynecologist consultation.

This information is for reference only and is not a medical service or diagnosis.