Estimate a baby's due date from your last period, a known conception date, or an IVF transfer date.
Last period: adds 280 days (40 weeks) to the first day of your last menstrual period, adjusting slightly if your cycle isn't exactly 28 days.
Conception date: adds 266 days (38 weeks) to the date of conception, since pregnancy is typically dated from ovulation rather than the last period.
IVF transfer: counts forward from the transfer date, accounting for the embryo's age at transfer (3 or 5 days) to line up with the same 38-week-from-conception estimate.
Only about 5% of babies arrive on their exact due date — treat this as a planning estimate, and confirm dates with your doctor or midwife.