For quick use the free ovulation calculator can be found at the bottom of page.

Disclaimer – ovulation calculator and ovulation calculators in general are not reliable as sole method of predicting ovulation.
To understand how an ovulation calculator is not reliable please continue reading.

Ovulation Calculator

Ovulation Calculator

Ovulation Calculator

An Ovulation Calculator is designed to help you predict your most fertile days of the month or menstrual cycle. Contrary to popular belief, an ovulation calculator is not as reliable as we would like to believe. Knowing your most fertile days in your cycle WILL increase your chances of getting pregnant by helping you determine the timing of your ovulation and peak fertility. Or to help decrease your chances of getting pregnant if you would rather not have a baby now. Menstrual periods vary from woman to woman and month to month. Feel free to use this Ovulation Calculator to compare against your other fertile signs and signals to verify the accuracy of this ovulation calculator.

How does an Ovulation Calculator work?

A Ovulation Calculator will show you your most fertile dates based on your last period date and your period length. The first day of your cycle begins with the first day of your period. The first day of your period is considered the first day you begin to bleed fully and is referred to as your cycle day 1. Your period length refers to the total number of days in your cycle from the start of your period to the last day in your cycle before your period begins.

A healthy menstrual cycle

A healthy menstrual cycle will average 21-35 days. Regular cycles is one indication ovulation has likely occurred. For cycles longer than 35 days, ovulation is either not occurring or occurring irregularly. While woman can expect ovulation to takes place, on average, about two weeks before your period, it can vary from 10-16 days before the onset of menstruation depending on the length of your luteal phase.


Ovulation is when a mature egg is released from the ovary, pushed down the fallopian tube, and is available to be fertilized. Approximately every month an egg will mature within one of your ovaries. During an “average” 28 day cycle, ovulation is usually expected to take place between cycle days 13-15. Based on this guideline, many women are taught to expect ovulation around day 14 of their menstrual cycle.

Ovulation Calculator not reliable as sole method of predicting ovulation

Many women, however, do not have average cycles and even those who usually do may see irregularities from time to time. This variation among women and from cycle to cycle means that there is really no simple “one-size-fits-all” mathematical formula to calculate your ovulation date. However, it is possible to learn how to identify your own ovulation date and fertile signs by examining your fertility signals. Using an ovulation calculator is not always the best way to predict your ovulation. Therefore it’s advised to use other methods along side an ovulation calculator to predict your peak fertility.

When does variation in ovulation become a problem?

When there isn’t enough time in your luteal phase to allow for an embryo to implant into your uterus resulting in a pregnancy. More obviously, when you aren’t ovulating at all. An anovulatory cycle is a menstrual cycle during which the ovaries do not release an oocyte, aka an egg. Meaning, ovulation does not take place. Chronic anovulation is a common cause of infertility.

Questions about your menstrual cycle or ovulation?

Contact Fertility Guide, Lin Weinberg. Get in touch now.

The Ovulation Calculator

Use our fertility calculator to calculate your most fertile days of the month. Simply fill in your Last Menstrual Period (cycle day 1 of your period) date, and your cycle length (the last day before your period began again) to populate your ovulation calculator predictions.