Progesterone levels are typically tested on specific days of a woman's menstrual cycle. The most common time to measure Progesterone is around day 21 of a 28-day cycle, counting from the first day of menstruation. This timing is based on the assumption that ovulation occurs on day 14. However, in women with irregular cycles or those undergoing fertility treatments, Progesterone testing may be done on different days to assess ovulation and Progesterone production. Additionally, if a woman suspects low Progesterone or is experiencing symptoms related to hormonal imbalances, a healthcare professional may recommend Progesterone testing at other times in the cycle to provide a more comprehensive evaluation. Ultimately, the timing of Progesterone testing should be determined by a healthcare professional based on individual circumstances and specific concerns.