How accurate is the due date?
An estimate. Most babies arrive within 2 weeks before or after. Only 4% deliver on exact due date.
Health Fitness
Pregnancy Calculator
Estimate pregnancy with quick inputs.
Fast, practical estimates
Adjust inputs for the most useful result.
What this calculator does
A pregnancy calculator tracks gestational progress from last menstrual period (LMP) through delivery. It shows current week, trimester, and estimated due date. Standard pregnancy is 40 weeks (280 days) from LMP.
How it works
Enter LMP. Calculator determines current gestational week, trimester, and days until due date.
Formula
Due Date = LMP + 280 days. Current Week = (Today - LMP) ÷ 7. Trimesters: 1-13 weeks, 14-26 weeks, 27-40 weeks.
Tips for using this calculator
- Accurate LMP improves due date accuracy
- First trimester ultrasound can refine dating
- Due date is an estimate—only 4% deliver on exact date
- Track prenatal appointments by gestational week
- Learn milestone timing for each trimester
Frequently asked questions
What if I don't know my LMP?
Early ultrasound can estimate gestational age within 3-5 days.
When does each trimester start?
First: weeks 1-13. Second: weeks 14-26. Third: weeks 27-40.