How to Calculate Ovulation on a Calendar

Tracking your menstrual cycle to identify when ovulation occurs can help you to achieve (or avoid) pregnancy 1. Women who have a regular cycle (28 days) are most likely to get accurate results when employing an ovulation calendar 1.

In addition to plotting the days when your period begins and ends, measuring basal body temperature and observing other signs of ovulation can help you identify your most fertile days, especially if you tend to have an irregular cycle 1.

Mark on the calendar when your period begins and ends each month.

If your period begins every 28 days, you probably have a regular cycle and can use the counting method to determine your most fertile day. Counting the day you began your period as day 1, find day 15 and circle it on the calendar. This is the day on which you're likely to be the most fertile.

If you do not have a regular menstrual cycle, or you wish to make your calculations more accurate, you will need to measure your basal body temperature with a basal body temperature thermometer.

Plot your basal body temperature on a calendar for each day of your menstrual cycle.

Locate the day on which your basal body temperature reaches its high point. Normally, you will be at your most fertile two or three days before this temperature spike occurs.

Use the temperature information you gathered during the previous month to predict where these high-fertility days will fall during the coming month. Continue to measure and record your basal body temperature to verify these predictions.


Tools such as fertility tests can also be helpful in determining ovulation.

If you have difficulty getting pregnant, consult your doctor.


Using an ovulation calendar will not reliably prevent pregnancy. Always use birth control if you do not wish to become pregnant.