There are many ways to calculate ovulation, but the most common method is to use the method of measuring basal body temperature. Basal body temperature refers to the time it takes for your body temperature to rise to 37 degrees when you wake up in the morning. The method of measuring basal body temperature is very simple. Just place the thermometer under your tongue, measure your temperature at the same time every day, and record it in your diary.

If you want to more accurately measure ovulation, you can use other methods, such as measuring the rate of change in body temperature or using methods to measure menstrual blood volume and menstrual cycles. These methods may produce different results for different women, so it's best to consult a doctor or professional advisor.

Measuring ovulation is not the only way. Women can have sexual intercourse within a few days before and after the dangerous period (i.e. ovulation) to increase the chance of fertility. However, women should also use contraception during dangerous periods because pregnancy may occur even if they have intercourse during safe periods.