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Ovulation Tracker

The Ovulation Calculator estimates the most probable ovulation/fertile window. Estimations are based on a woman’s last menstrual cycle. This calculator should not be used as a form of birth control.

First day of last menstrual cycle: Cycle length:


How is this information calculated?

Ovulation is the process of the release of an egg from the ovary. Ovulation occurs approximately 14 days before the start of the next menstrual cycle, although this number can vary from person to person and cycle to cycle.

To calculate the estimated ovulation date, you need to know the first day of the last menstrual cycle and the cycle length (the number of days between the first day of one cycle and the first day of the next cycle). The cycle length is then divided by 2 and added to the first day of the menstrual cycle to estimate the ovulation date.

The due date of a baby born from this cycle is calculated by adding 280 days (40 weeks) to the estimated ovulation date. This due date is just an estimate and actual birth can occur several days before or after the due date.

Another method that is sometimes used to estimate the due date is based on the LMP and involves counting back three calendar months and adding seven days to the result.

For example, if the LMP was January 1, the due date would be calculated as:

  • subtract 3 months from January 1, which gives October 1
  • add 7 days to October 1, which gives October 8
  • so the estimated due date is October 8

This method is also only an estimate and may not be as accurate as the first method. The due date can also be confirmed using ultrasound during pregnancy.