This calculator estimates your due date from the first day of your last period, from a known conception date, or from the date of an IVF embryo transfer. A due date is a midpoint rather than a deadline, and only a dating scan can confirm it.
This is an estimate based on an average 280-day pregnancy. Only a dating scan can confirm how far along a pregnancy is, and a due date is a midpoint, not a deadline — most babies arrive in the two weeks either side of it. Please use this alongside your doctor's advice, not instead of it.
How a due date is worked out
A pregnancy is counted as 280 days — 40 weeks — from the first day of the last menstrual period. That figure assumes ovulation around day 14, so this calculator adjusts it when your cycle is shorter or longer than 28 days.
After IVF the arithmetic is more exact, because the date of fertilisation is known: the due date is 266 days from conception, counted back from the age of the embryo at transfer.
When to see a doctor rather than a calculator
An estimate is a starting point for a conversation, not a substitute for one. Book a dating scan to confirm how far along you are, and speak to your doctor about any bleeding, pain or reduced movement whatever the dates say.