Calculators
Due Date Calculator
Estimate your due date from your last period, conception date, or IVF transfer, and see how far along you are with a milestone timeline.
Pick a date to estimate your due date.
This is an estimate based on an average 28 day cycle. Only about 4 in 100 babies arrive on the exact due date. Your doctor confirms dating with an ultrasound.
How it works
The standard method, called Naegele's rule, counts 280 days (40 weeks) from the first day of your last period. Conception and IVF dates skip the early part, so they count from a known later point.
From last period: due = LMP + 280 daysFrom conception: due = conception + 266 daysIVF day-5 transfer: due = transfer + 261 daysCurrent week and trimester are measured from the same start point, which is why pregnancy is usually described as 40 weeks even though development takes about 38.
Last period to due date
Example due dates for a few last-period dates, using the 280 day rule.
| Last period | Estimated due date |
|---|---|
| Jan 1, 2026 | Oct 8, 2026 |
| Mar 15, 2026 | Dec 20, 2026 |
| Jun 1, 2026 | Mar 8, 2027 |
| Sep 10, 2026 | Jun 17, 2027 |
Frequently asked questions
How accurate is a due date?
It is an estimate. Only about 1 in 20 babies arrive on the exact date, and most births happen within two weeks either side. An early ultrasound gives the most reliable dating.
What counts as full term?
Full term is 37 to 42 weeks. Babies born before 37 weeks are preterm, and pregnancies past 42 weeks are post-term and usually monitored closely.
What if my cycle is irregular?
The last-period method assumes a 28 day cycle with ovulation around day 14. If your cycle is longer, shorter, or irregular, the conception date or an ultrasound gives a better estimate.
How does the IVF date change things?
With IVF the embryo age is known, so dating is precise. A day-5 blastocyst transfer counts as 19 days of gestation already passed, which the calculator builds in.
Why is the due date 40 weeks from my last period?
Dating starts from the last period, about two weeks before conception, so the convention adds roughly 280 days even though the baby develops for about 38 weeks.