Pregnancy Due Date Calculator
Find your estimated due date and how many weeks pregnant you are today, from your last period, conception or IVF transfer date.
How the due date is calculated
Doctors count pregnancy from the first day of your last menstrual period (LMP), about two weeks before conception. Adding 280 days (40 weeks) to the LMP gives the estimated due date, a method known as Naegele's rule. If your cycle is longer or shorter than 28 days, the date moves by the difference. From a known conception date the due date is 266 days later; after IVF it is 261 days after a day-5 embryo transfer or 263 days after a day-3 transfer.
Trimesters and term
| Stage | Weeks |
|---|---|
| First trimester | 0 – 13w 6d |
| Second trimester | 14 – 27w 6d |
| Third trimester | 28 – 40+ |
| Early term | 37w 0d – 38w 6d |
| Full term | 39w 0d – 40w 6d |
| Late term | 41w 0d – 41w 6d |
| Post-term | 42 weeks and later |
Term definitions follow the American College of Obstetricians and Gynecologists (ACOG).
Frequently asked questions
How accurate is a due date?
It's an estimate: only about 4–5% of babies are born on their due date, and most arrive within two weeks either side. A first-trimester ultrasound is the most accurate way to date a pregnancy.
Why does pregnancy count from my last period?
Because the date of the last period is usually known while the date of conception isn't. Counting from the LMP adds about two weeks before conception, so a 40-week pregnancy is about 38 weeks from conception.
How do I calculate my due date after IVF?
Add 261 days to the transfer date for a day-5 (blastocyst) embryo, or 263 days for a day-3 embryo. Choose the IVF option above.