To calculate your fertile window, women with a 28-day cycle should count 14 days from the date they last menstruated (with the first menstruation day counting as Day 1). Ovulation will have occurred between 3 days before and 3 days after that 14th day, which is considered to be the fertile window.

Knowing your fertile window is important for women who are trying to get pregnant, as sex during this time is associated with a higher chance for pregnancy. Knowing the times of the month that you are most and least fertile can also be beneficial as a birth control method, although this is not a fully reliable method. Learn more about other birth control options you can use instead.

To determine your fertile window, use our online calculator to determine when your fertile window is:

Please note that this calculator is only accurate for women with a regular, 28-day cycle.

What is a fertile period?

A fertile period is the time of the menstrual cycle when ovulation occurs. During this time, women have the greatest chance of getting pregnant. It lasts for about 6 days, and occurs 10 to 14 ays after the first day of menstruation.

Irregular periods

Calculating a fertile window with an irregular cycle is not as accurate, which can be a disadvantage if trying to get pregnant or avoid pregnancy. Because menstruation does not occur at similar times, calculations can be off.

Nonetheless, one way to know approximately when the fertile window occurs during irregular cycles is to track the duration of each cycle for one year, and then subtract 18 days form the shortest cycle and 11 days from the longest.

For example: If your shortest cycle was 22 days, and your longest was 28 days, then 22 - 18 = 4 and 28 - 11 = 17. This means your fertile window will occur between the 4th and 17th days of your cycle.

A more accurate way of knowing when your fertile window will occur when your cycle is irregular is performing an ovulation test. This can be especially beneficial to women who are trying to get pregnant. This test can be purchased at the pharmacy. Women should also be aware of the signs of ovulation, like having egg-white discharge. Learn more about the other signs and symptoms of ovulation that occur when you are most fertile.

How do I know if I am in my fertile window?

A fertile window can be identified through some signs, such as:

Increased vaginal discharge;
Increased body temperature;
Increased appetite;
Increased libido.

The signs and symptoms of the fertile period occur when the egg is released by the ovary and reaches the fallopian tubes.