Ovulation Calculator

Using a Calculators

Women who are trying to become pregnant can use ovulation calculators to help figure out when sexual intercourse is most likely to result in pregnancy. Women who do not want to become pregnant should not rely on calculators; they’re not accurate enough to prevent pregnancy.

How Ovulation Calculators Work

Ovulation calculators require you to know the length of your menstrual cycle and the date your last period started. One menstrual cycle is the number of days from the first day of bleeding in one period until the day before the first day of bleeding in the next period.

On average, ovulation occurs about 14-16 days before a woman’s period starts. The calculator uses this information plus your own cycle length to estimate when you will ovulate.

Some calculators give a single date for ovulation. Others give a range of days. Some also give you the due date of the baby, in case you conceive!

If you’re using a calculator to decide when to have sexual intercourse, keep in mind that:

• The ovulation date probably isn’t exact.
• Sperm remain active in a woman’s uterus for about three days after intercourse.
• You’re most fertile for about three days before and one day after you ovulate.

Start early and continue a few days past the estimated dates to increase your chances of getting pregnant!

Accuracy

The accuracy of an ovulation calculator depends on how regular your menstrual cycles are and whether you ovulate at the expected time.

Calculators work best for women who have very regular cycles. They’re not helpful for women with very short (less than 21 days), very long (more than 35 days), or very irregular cycles.

Also, since ovulation isn’t completely predictable, remember that a calculator is really only giving an educated guess. There can be a lot of variability from one woman to another, and even from cycle to cycle. Using another method, like charting changes in your body temperature, observing changes in vaginal mucus, or doing monthly urine tests, can help you be more certain of your fertile days. You can find more information about these methods in the LoveToKnow articles on Ovulation Predictors and Signs of Ovulation.

Calculators for Gender Selection

Some web sites that offer ovulation calculators claim you can choose your baby’s sex by choosing which day to have intercourse. This is based on the idea that sperm with X chromosomes (which make girl babies) and sperm with Y chromosomes (which make boy babies) have different times when they’re most likely to fertilize an egg.

But don’t choose the color for the nursery based on an ovulation calculator. First of all, they aren’t precise enough to pinpoint the exact day of ovulation, which would be necessary for the sex selection theory to work.

More importantly, medical studies haven’t proven that the timing of sexual intercourse makes a difference. And if it does, it’s probably the opposite of what ovulation calculators claim. Many web sites with ovulation calculators tell you to have sex near the time of ovulation if you want a boy. In fact, there is some evidence that having sexual intercourse in the two days leading up to ovulation makes it more likely you'll have a girl. Even if there is a difference, however, it’s very small. No matter when you conceive, you should still expect the baby’s sex to be a surprise.

Where to Find an Online Calculator

• Click here for a calculator from the National Women’s Health Information Center
• Click here for a calculator from the March of Dimes