On day 21 of a typical 28-day menstrual cycle, a normal Progesterone level for a non-pregnant woman is generally considered to be 5-20 ng/mL (nanograms per milliliter). This timing assumes that ovulation has occurred on day 14. However, it is important to note that Progesterone levels can vary between individuals, and the reference ranges may differ based on the specific laboratory or healthcare provider. Additionally, Progesterone levels can be influenced by various factors, such as underlying medical conditions, medications, and hormonal imbalances. Therefore, it is essential to interpret Progesterone levels in conjunction with the individual's overall clinical picture and specific circumstances. Consulting a healthcare professional who can assess the results and provide appropriate guidance is crucial for accurate interpretation and evaluation of Progesterone levels.