Pregnancy Due Date Calculator
Enter the first day of your last menstrual period (LMP) and your usual cycle length to estimate your due date, your current week and when each trimester begins.
How the due date is estimated
Healthcare providers usually use Naegele’s rule: add 280 days (40 weeks) to the first day of your last period. That assumes a 28-day cycle with ovulation around day 14. If your cycle is longer or shorter, the calculator shifts the date by the difference.
Trimesters
| Trimester | Weeks |
|---|---|
| First | Weeks 1 to 13 |
| Second | Weeks 14 to 27 |
| Third | Week 28 to birth |
How accurate is it?
Only a small share of babies are born exactly on their due date; most arrive within about two weeks before or after. An early ultrasound measurement is usually more accurate, and your provider may adjust your due date after your dating scan.
This calculator is for information only and does not replace advice from your doctor, midwife or nurse practitioner. Learn more: how is a due date calculated?