One of the first questions after a positive pregnancy test is "When is the baby due?" This free due date calculator gives you an estimate in three ways. Most people use the first day of their last menstrual period (LMP): the standard method, known as Naegele's rule, adds 280 days (40 weeks), and we adjust it if your cycle is usually longer or shorter than 28 days. If you know your conception date, we add 266 days. If you conceived through IVF, enter the transfer date and whether it was a day-3 or day-5 embryo for a more precise figure. Along with the estimated due date, you'll see how many weeks and days pregnant you are today, which trimester you're in, and when the second and third trimesters begin. Please keep this in perspective: only about 4% to 5% of babies arrive on their exact due date, and most are born within a week or two either side. Your midwife, obstetrician or GP will usually confirm or adjust the date with a dating ultrasound scan in the first trimester, and that date takes priority. This tool is for information only and isn't medical advice. Nothing you enter is stored or sent.
Estimate your due date
An estimate for information only. Your healthcare provider’s dating scan takes priority.
How the due date is calculated
- Last period: LMP + 280 days, plus (cycle length − 28) days.
- Conception: conception date + 266 days.
- IVF: transfer date + 263 days (day-3) or + 261 days (day-5).
Trimesters
| First | Weeks 1–13 |
| Second | Weeks 14–27 |
| Third | Week 28 to birth |
FAQ
How accurate is a due date?
It’s an estimate. Only a small share of babies are born on the exact day; most arrive within about two weeks either side.
Why do weeks count from my last period?
By convention, pregnancy is dated from the LMP, about two weeks before conception, so you’re “4 weeks pregnant†around the time of a missed period.
My scan gave a different date. Which is right?
Follow your provider. An early ultrasound is generally more accurate than period-based dating.
Is my information stored?
No. The calculation runs in your browser.
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