Pregnancy Due Date Calculator
By Santaji GadepatilinUpdated October 27, 2026
How to use this calculator
Choose the first day of your last period and your average cycle length. Your estimated due date, how many weeks pregnant you are today, and the days remaining are calculated.
Formula (Naegele’s rule)
Due date = LMP + 280 days + (cycle length − 28)
Trimesters
| Trimester | Weeks |
|---|---|
| First | 1–13 |
| Second | 14–27 |
| Third | 28–40 |
This tool gives an estimate only. Your doctor or midwife will confirm your due date, usually with an ultrasound scan.
Frequently asked questions
How is the due date calculated?
By Naegele's rule — 280 days (40 weeks) after the first day of the last period, adjusted for cycles longer or shorter than 28 days.
How accurate is it?
Only about 4–5% of babies arrive on their due date; most are born within two weeks either side. An early ultrasound gives a more accurate date.
Why count from the last period, not conception?
The period date is usually known. Conception typically happens about two weeks later, so you are counted as "2 weeks pregnant" at conception.