The exact time of ovulation can be determined by measuring the basal body temperature. How to measure? From the first day to before the day of the next period is one full menstruation period. Each morning during the cycle, measure the temperature under your tongue for five minutes without drinking, eating, speaking and going to the bathroom. Prior to ovulation, the temperature is about 36.5℃, whilst after ovulation it can reach around 37℃ until the next period. Temperature will drop a little during ovulation, which means the day the temperature drops is the day of ovulation.
If ovulation is normal, the body temperature curve should go both ways, which means the temperature should be 36.5℃ to 37℃ in the first half of menstruation, and then go higher to 36.8℃ to 37.5℃ after ovulation.