Due date
Estimated due date, trimesters and current week, from your last period.
- Instant
- Free
- Private (processed locally)
- No sign-up
One date, three milestones, and your current week
For two centuries, Naegele’s rule has estimated the due date: last period + 280 days. The tool applies it, places the trimester boundaries, and if your pregnancy is underway, shows today’s gestational week — the one your midwife will use.
-
Pick the mode
Last menstrual period (LMP), or conception date if you know it.
-
Enter the date
The due date and milestones compute immediately.
-
Track your progress
Current weeks + days and trimester are displayed.
Example: LMP on January 1st
| Milestone | Date |
|---|---|
| End of 1st trimester (week 13) | April 2 |
| End of 2nd trimester (week 27) | July 9 |
| Estimated due date (week 40) | October 8 |
An indicative estimate: only the dating ultrasound is the medical reference, and 90% of births occur within 2 weeks of the due date. This calculation does not replace follow-up by your midwife or doctor.
Frequently asked questions
Where does the 280-day rule come from?
From Naegele’s rule (1812): a pregnancy lasts on average 40 weeks (280 days) from the first day of the last period, i.e. 38 weeks (266 days) from conception — ovulation occurring about 14 days after the cycle starts.
Gestational age vs fetal age: what’s the difference?
Gestational age counts from the last period; fetal age from conception. Gestational = fetal + 2 weeks. Medical follow-up almost always uses gestational weeks — which is also what this tool displays.
How reliable is this estimate?
Only about 4-5% of babies are born on their exact due date; 90% are born within the surrounding two weeks. The first-trimester dating ultrasound (crown-rump length) refines the estimate to ±5 days and takes precedence over the calculation.
What if my cycles aren’t 28 days?
Naegele’s rule assumes a 28-day cycle with ovulation on day 14. With longer or irregular cycles, the calculated term shifts accordingly — use the “conception date” mode if you know it, or rely on the dating ultrasound.