Pregnancy Due Date Calculator
Estimate your pregnancy due date, conception date, and current gestational age based on your last menstrual period.
How Due Dates are Calculated
Medical professionals calculate your Estimated Date of Delivery (EDD) using a method known as Naegele's rule. This standard obstetric formula bases the calculation on the first day of your Last Menstrual Period (LMP).
Naegele's Rule
The standard formula assumes a 28-day menstrual cycle. To calculate the due date:
- Take the first day of the Last Menstrual Period (LMP)
- Add 7 days
- Subtract 3 months
- Add 1 year
If your cycle is longer or shorter than 28 days, adjustments must be made (adding or subtracting the difference).
Gestational Age vs. Fetal Age
In the medical world, you are technically considered "pregnant" starting from the date of your LMP—about two weeks before you actually conceive. Therefore, your gestational age is always about two weeks older than the true age of the fetus.
Frequently Asked Questions
How accurate is an estimated due date?
It is only an estimate. Only about 4% to 5% of babies are born exactly on their estimated due date. The vast majority arrive somewhere between 37 and 42 weeks of gestation.