Conception Date Calculator
Work backwards from your due date to estimate when you actually conceived — plus the likely intercourse window and the last period your dates are built on.
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Estimated conception date
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How conception is estimated from a due date
A due date is set 280 days after the last menstrual period, and conception typically happens around ovulation — about 14 days in. Subtracting 266 days from the due date therefore lands on the most likely conception day. Because ovulation timing varies, the honest answer is a window of several days, and sperm can survive up to 5 days, so the intercourse that led to conception may have been a few days before conception itself.