HEALTH · PREGNANCY DUE DATE
Pregnancy Due Date Calculator
Estimate your baby's due date using Naegele's Rule (LMP + 280 days) or your conception date. Adjusts for non-28-day cycles.
About This Calculator
Naegele's Rule — the clinical standard since the 19th century — estimates your due date as 280 days (40 weeks) from the first day of your last menstrual period. If you know your conception or IVF transfer date, the calculator uses that instead. The result is always an estimate; ultrasound dating is more accurate, especially after the first trimester.
How It Works
Enter the first day of your last menstrual period and your typical cycle length. For cycles longer or shorter than 28 days the calculator adjusts the due date by the difference — a 30-day cycle shifts the EDD two days later. If you know your conception date, switch to conception mode (EDD = conception + 266 days).
The Formula
EDD = LMP + 280 + (cycle_length − 28)
- LMP
- first day of last menstrual period
- cycle_length
- typical cycle length in days (default 28)
Frequently Asked Questions
- How accurate is the due date estimate?
- Naegele's Rule gives a statistical average — only about 5% of babies are born on their estimated due date, and a normal delivery window spans weeks 37–42. Ultrasound dating between 8 and 14 weeks is more accurate and supersedes the LMP estimate per ACOG guidance.
- Why does cycle length matter?
- The formula assumes ovulation occurs 14 days before the next period. If your cycle is 30 days instead of 28, ovulation happens 2 days later — and conception, and therefore the due date, shifts by the same 2 days.
- What if I used IVF?
- Switch to Conception mode and enter your embryo transfer date. For a day-5 blastocyst transfer, the transfer date is used directly. For a day-3 embryo, add 2 days to the transfer date before entering it.