Pregnancy Due Date Calculator
Estimate your baby's due date and current gestational age from your last period.
Inputs
Estimated Due Date
—
Gestational Age Today
Enter your last period date
Trimester
Step by step
Waiting for the first day of your last period
Your due date is counted forward from that date, so it's the one input this calculator can't estimate for you.
How it works
Due date is estimated with Naegele's rule: 280 days (40 weeks) from the first day of your last menstrual period, adjusted if your cycle differs from 28 days.
Formula
Naegele's rule
EDD = LMP + 280 days + (cycle length − 28 days)
- 28
- Standard cycle length assumed by Naegele's rule
- 280
- Standard gestational period in days (40 weeks)
- EDD
- Estimated due date
- LMP
- First day of last menstrual period
- C
- Average cycle length in days
This is an estimate only and not a substitute for professional prenatal care. Always confirm your due date with your doctor or midwife.
Frequently Asked Questions
How accurate is the due date?
Only about 4% of babies arrive exactly on their due date. It's a best estimate — most births occur within two weeks either side.
What if my cycle isn't 28 days?
This calculator shifts the due date by the difference between your average cycle length and the standard 28 days, which improves the estimate for longer or shorter cycles.