Pregnancy due date calculator
Dating a pregnancy counts forward 280 days from the last period, adjusted for cycle length. You get the estimated due date, how far along you are in completed weeks and days, and when each milestone falls.
- How far along
- 10w0d
- Trimester
- 1
- Days to go
- 210 days
- Weeks to go
- 30
- Progress
- 25 %
- Estimated conception
- August 26, 2026
- 24 weeks
- January 27, 2027
- Full term, 37 weeks
- April 28, 2027
| Milestone | Date |
|---|---|
| milestone:t1end | November 11, 2026 |
| milestone:t2end | February 17, 2027 |
| milestone:viable | January 27, 2027 |
| milestone:term | April 28, 2027 |
| milestone:due | May 19, 2027 |
| milestone:late | June 2, 2027 |
An estimate, not a medical assessment. Your midwife or doctor's dating, based on examination and ultrasound, is the one that counts.
The formula
Naegele's rule: due date = first day of last period + 280 days, plus the difference between your cycle length and 28 days. Conception dating anchors 14 days later, so it adds 266 days instead. Gestational age is written as completed weeks and days, so 13w2d.
Worked example
A last period starting 1 January with a 28-day cycle gives a due date of 8 October. On 20 October of the previous pattern you would be 13w2d along, in the second trimester.
How to use it
- 1Use the first day of your last period, not the day it ended.
- 2Switch to conception dating if you know the date — after IVF, for instance — since it removes the cycle assumption.
- 3If you have had a dating scan, its date replaces any calculation. Early ultrasound measurement is more accurate than counting.
Questions people ask
How likely is the baby to arrive on the due date?
Around one in twenty births falls on it. Most arrive within two weeks either side, which is why 37 to 42 weeks is treated as the normal range rather than a single date.
Why does my clinic's date differ from this?
A dating ultrasound in the first trimester measures the fetus directly and overrides any calculation from dates. If the two differ by more than about five days, the scan is normally used.
Last reviewed: 2026-10-20