Ovulation Calculator

The Ovulation Calculator estimates the days in your cycle when conception is most likely.

Enter the first day of your last menstrual period and your average cycle length, and the tool works out your predicted ovulation day, your fertile window of roughly six days, and the expected start of your next period.

It uses the standard approach of counting back a luteal phase (about 14 days) from the next period to find ovulation, and treats the five days before ovulation plus ovulation day itself as the fertile window, because sperm can survive for several days inside the body.

You can adjust both the cycle length and the luteal phase to better match your own pattern, which is useful if your cycles run shorter or longer than the textbook 28 days.

The result highlights how many days remain until ovulation and whether today already falls inside your fertile window, so you can plan around it.

Everything is calculated locally in your browser using fixed-date arithmetic, so your personal cycle information is never uploaded, logged or stored anywhere.

Please remember this is a general estimate based on averages, not a diagnosis or a contraceptive method — real cycles vary from month to month and ovulation can shift.

For trying to conceive, avoiding pregnancy, or any health concern, talk to a healthcare professional.