Due Date Calculator: Pregnancy Due Date Accurately
Estimate your baby's due date using Naegele's Rule or ultrasound data. Learn how gestational age is calculated and what the first, second, and third trimesters mean.
How is a Pregnancy Due Date Calculated?
A pregnancy due date (estimated date of delivery, or EDD) is typically calculated from the first day of the last menstrual period (LMP). The average human pregnancy lasts 280 days (40 weeks) from LMP. This is known as Naegele's Rule, the global standard for estimating due dates.
👶 Due Date Calculator
Use our free calculator for instant, accurate results.
📐 Formula
EDD = LMP + 280 days
Naegele's Rule: Add 1 year, subtract 3 months, add 7 days to the LMP. Assumes a regular 28-day cycle with ovulation on day 14.
📝 Worked Example
LMP = January 1, 2026:
EDD = January 1 + 280 days = October 8, 2026
Or: Jan 1 + 1 year − 3 months + 7 days = Oct 8, 2026 ✓
📝 How to Use the Calculator
❓ FAQ
Is a due date an exact date?
Only about 5% of babies are born on their exact due date. The EDD marks the middle of a normal delivery window (37–42 weeks).
What if I don't know my LMP?
An early ultrasound (before 12 weeks) can establish gestational age from fetal measurements and is often more accurate.
Veer Kumavat
Founder & AuthorVeer is a 14-year-old student from Nashik, Maharashtra, who built SciFi Calculators to help students worldwide master STEM subjects. He is passionate about making complex science and math problems accessible through intuitive digital tools.