Due Date Calculator

Calculate estimated due date from conception date.

Gestational age is calculated from the first day of LMP

How to Do It Manually

Due date is estimated as 280 days (40 weeks) from the first day of the last menstrual period. Naegele's rule provides an easy approximation.

Due Date ≈ Last Menstrual Period (LMP) + 280 days (or + 9 months + 7 days)
  1. Note the first day of your last menstrual period.
  2. Add 280 days, or use Naegele's rule: add 1 year, subtract 3 months, add 7 days.
  3. Confirm with ultrasound dating in the first trimester.

Frequently Asked Questions

Is my due date accurate?

Only about 5% of babies are born on the due date. It's an estimate; delivery within ±2 weeks is normal.

What if I don't know my last period date?

Ultrasound dating in the first trimester is most accurate. Use this calculator for estimates only.