EDD Calculator
Calculate your Estimated Due Date using Naegele's Rule from your Last Menstrual Period.
How to Use the EDD Calculator
Enter the first day of your last menstrual period (LMP) and click Calculate EDD. The calculator will show your estimated due date along with your current pregnancy week, trimester and other details.
What Is Naegele's Rule?
Naegele's Rule is the standard method used to estimate a pregnancy due date. It was first described by German obstetrician Franz Karl Naegele in the early 19th century.
Formula: EDD = LMP + 1 year − 3 months + 7 days
This is mathematically equivalent to adding 280 days (40 weeks) to the LMP date.
Assumptions
- A regular 28-day menstrual cycle
- Ovulation occurring on day 14 of the cycle
- Conception occurring near ovulation
For irregular cycles or cycles significantly longer or shorter than 28 days, the estimated due date may be less accurate.
Sources & References
- Naegele FC. "Lehrbuch der Geburtshülfe für Hebammen." 1830.
- American College of Obstetricians and Gynecologists (ACOG) — Committee Opinion on Methods for Estimating the Due Date.
- National Health Service (NHS) — Your due date.
Frequently Asked Questions
What does EDD stand for?
EDD stands for Estimated Due Date — the approximate date when your baby is expected to be born, calculated from the first day of your last menstrual period.
How accurate is Naegele's Rule?
Naegele's Rule provides a reasonable estimate for women with regular 28-day cycles. However, only about 5% of babies are born on their EDD. An ultrasound in the first trimester can provide a more accurate due date.
What if my cycle is not 28 days?
Naegele's Rule assumes a 28-day cycle. If your cycle is longer or shorter, the estimated due date may differ. Discuss your cycle length with your healthcare provider for a more personalised estimate.