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What is basal temperature and how to measure it?
Last reviewed: 08.07.2025
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Basal temperature is measured in the rectum. It can be used to determine more accurately when ovulation occurs. To do this, measure the temperature in the rectum every day (morning and evening). Do not insert the thermometer too deeply into the anus. It is enough to insert it 2-3 cm. Record the results of the measurements in a notebook so that you get a graph where the ordinate axis (the one that goes up) plots the temperature in the rectum, and the abscissa axis (the one that is horizontal) plots the days of the menstrual cycle from the first to the 28th day (if you have a shorter or longer cycle, then until the last day of your cycle).
At the same time, during ovulation (approximately on the 14th day), the basal temperature increases by 0.5 °C. In addition, with the help of this method, it is sometimes possible to determine that ovulation does not occur at all. This happens with infertility. Then, an almost straight line appears on the graph without an increase in temperature during the period of expected ovulation.