How accurate is the due date?
Only 4% of babies arrive on due date. Most come within 2 weeks. Ultrasound refines accuracy.
Health Fitness
Due Date Calculator
Calculate due date with your details.
Personalized estimate
Use realistic inputs for the most useful results.
What this calculator does
Pregnancy due date uses Naegele's rule: LMP + 280 days (40 weeks). Most babies arrive within 2 weeks of estimated date.
How it works
Add 280 days to first day of last menstrual period. Ultrasound in first trimester can refine estimate.
Formula
Due Date = LMP + 280 days. Or: LMP + 7 days - 3 months + 1 year.
Tips for using this calculator
- Track LMP accurately for best estimate
- First trimester ultrasound is most accurate (±3-5 days)
- Due date is an estimate—expect 37-42 week range
- Plan for 2-week window before and after
- Learn warning signs requiring medical attention
Frequently asked questions
What if I don't know my LMP?
Early ultrasound can estimate gestational age and calculate due date.
Can the due date change?
Yes, doctors may adjust based on ultrasound measurements, especially if significantly different from LMP calculation.