The method to work out your due date from your conception date is to add 266 days to the date of conception. This will give you a rough guide of when your baby is due to be born.
When the conception date is known, the due date is estimated by adding 266 days (38 weeks) to the conception date. This differs from the LMP method, which adds 280 days, because conception typically occurs about two weeks after the start of the last menstrual period.
The LMP method adds 280 days to the first day of the last period, while the conception method adds 266 days from the known conception date. Both methods should yield the same estimated due date because the LMP method implicitly assumes conception occurs 14 days after the period begins.
If you know your exact conception date (for example, from IVF or precise tracking), this method can be more accurate than the LMP method because it eliminates the uncertainty around ovulation timing. However, due dates are always estimates, and only about 5% of babies are born on their predicted due date.
Conception occurs when a sperm fertilizes an egg, which typically happens within 12 to 24 hours of ovulation. Ovulation usually takes place 12 to 16 days before the next expected period. In a standard 28-day cycle, this means ovulation and potential conception occur around day 14.
Yes, the conception date method is particularly well-suited for IVF pregnancies because the exact date of egg retrieval and fertilization is known. For IVF, the due date is typically calculated as 266 days from the conception date (or 263 days for day-3 embryo transfers and 261 days for day-5 blastocyst transfers).