Question: how to calculate gestational weeks in pregnancy manually?
Answer: Gestational age (written with both weeks and days, eg. 39 weeks and 0 days) is calculated using the best obstetrical Estimated Due Date (EDD) based on the following formula: Gestational Age = (280 - (EDD - Reference Date)) / 7 (source: American College of Obstetricians and Gynecologists reVITALize Initiative).