How Does the Calculator Work?
Our calculator uses Naegele's rule, which is the standard method used by obstetricians and midwives worldwide. It calculates your Estimated Due Date (EDD) by adding exactly 280 days (40 weeks) to the first day of your Last Menstrual Period (LMP).
Why Do We Use the LMP?
You might wonder why pregnancy is calculated from the start of your last period, rather than the date of conception. This is because most women do not know exactly when they ovulated or conceived, but they usually remember the start of their last period. As a result, the first two weeks of your "pregnancy" actually take place before you even conceive!
What if my cycle isn't 28 days?
Naegele's rule assumes a perfectly average 28-day menstrual cycle. However, if your cycle is longer or shorter, your ovulation date shifts. Our calculator allows you to input your average cycle length. If your cycle is 30 days, we add 2 extra days to your due date. If it is 26 days, we subtract 2 days.
Important Note About Due Dates
Your Estimated Due Date is just that—an estimate. Only about 5% of babies are born exactly on their due date. A pregnancy is considered full-term at 37 weeks, and it is completely normal to go into labor anytime between 37 and 42 weeks. If you receive an early ultrasound, your doctor may adjust your EDD based on the baby's measurements.