Calculators » Health » Fertile Window Calendar

Ovulation Calculator

Our online tools will provide quick answers to your calculation and conversion needs. On this page, couples who want to have a baby can calculate the likely occurrence of fertile days (fertile window) and ovulation during the menstrual cycle.

Enter the first day of your last period (yyyy-mm-dd):

By adding your average cycle length, you can calculate for future dates to make your own private ovulation calendar. Use our date calculator to add dates quickly.

To achieve pregnancy, you should also closely monitor the fertility signs.

Android: Use this ovulation calculator offline with our all-in-one calculator app.


Ovulation Calculator - Methodology

The calculation on this page is based on the calendar based Standard Days method (SDM), a fertility awareness-based family planning method. By this method, it is estimated that women with most menstrual cycles between 26 and 32 days are fertile during days 8-19.

SDM is based on research that identifies the fertile "window" of a woman's menstrual cycle during which she can become pregnant. Usually, this "fertile window" begins approximately five days prior to ovulation and lasts up to 24 hours after ovulation. At least 88% of ovulations occur within +/- 3 days of the mid-point day of the menstrual cycle.

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