How Is My Due Date Calculated?
Your estimated due date (EDD) is typically calculated using Naegele's rule. This method is based on the first day of your last menstrual period (LMP) and assumes a regular 28-day cycle. While it's a widely used and simple method, it's important to remember that it's only an estimation.
Naegele's Rule Explained
The calculation is as follows:
- Start with the first day of your LMP.
- Add one year.
- Subtract three months.
- Add seven days.
A simpler way to think about it is just adding 280 days (or 40 weeks) to the first day of your LMP. Our calculator automates this for you. It also gives you an estimate of how far along you are in your pregnancy based on today's date.
Why Is It Just an Estimate?
The due date is an estimate because it's based on the assumption of a 28-day cycle with ovulation occurring on day 14. However, many women have cycles that are longer or shorter, and ovulation can vary. Only a small percentage of babies are born on their exact due date. Your doctor or midwife may provide a more accurate due date based on an ultrasound scan. This calculator is a helpful guide, but it is not a substitute for professional medical advice.