Conception Calculator
Our conception calculator, also known as a reverse due date calculator, is the answer to the question "When did I conceive?" as it estimates when your pregnancy was conceived.
When calculating conception based on the due date, we subtract 266 days (38 weeks). When using the last menstrual period, we add 14 days. For ultrasound dates, we first determine the LMP by subtracting the gestational age, then add 14 days to estimate conception. For IVF, the conception date is the egg retrieval date - for transfer dates, we subtract the embryo age (3 or 5 days).
The resulting date is your estimated day of ovulation. Since conception occurs soon after ovulation, this is the most likely date of conception. Your estimated conception window is 3 days before and 3 days after your estimated date of ovulation (EDO).
If you are not currently pregnant, use our Ovulation Calendar instead.