Congratulations on your pregnancy! One of the first and most exciting questions is, 'When will my baby arrive?' Your estimated due date (EDD) is the first major milestone on this incredible journey. Our Due Date Calculator is a simple tool designed to give you this special date, helping you and your healthcare provider plan for the months ahead.
This calculator uses the same methods that doctors and midwives use to estimate your due date, giving you a reliable starting point for your pregnancy timeline.
How to Calculate Your Due Date
To calculate your estimated due date, our tool needs just a couple of key details:
- The First Day of Your Last Menstrual Period (LMP): This is the universal starting point for pregnancy dating in the medical community. Select the first day you started bleeding on your most recent period.
- Your Average Cycle Length: While the standard calculation assumes a 28-day cycle, we know everyone is different. Entering your typical cycle length will adjust the calculation for a more personalized and accurate estimate.
The calculator will then provide you with your estimated due date and tell you how many weeks pregnant you are.
The Science Behind the Calculation: Naegele's Rule
For centuries, doctors have used a method called Naegele's Rule to estimate due dates. The rule works by taking the first day of your LMP, subtracting three months, and adding seven days. This calculation is based on a 40-week (280-day) pregnancy. Our calculator uses an adapted version of this rule that also accounts for your unique cycle length, providing a more precise estimate than the standard one-size-fits-all approach.
Why Your Due Date is an *Estimate*
It's exciting to have a date to circle on the calendar, but it's crucial to remember that your EDD is an estimate, not an expiration date! Only about 5% of babies are born on their actual due date. The main purpose of your due date is to serve as a guide for your healthcare provider to track your baby's growth, schedule important tests and screenings at the right time, and monitor your overall progress. A healthy, full-term pregnancy can last anywhere from 37 to 42 weeks, so think of your due date as the center of a 'due window.'
What If You Have Irregular Cycles or Don't Know Your LMP?
If you can't remember your last period or have highly irregular cycles, the LMP method can be inaccurate. In these cases, the most reliable way to determine your due date is with a first-trimester ultrasound. A doctor will measure the baby's crown-rump length to accurately date the pregnancy based on the baby's actual size. This ultrasound-based due date will then be used for the rest of your pregnancy.
Important Medical Notes
This calculator provides a reliable estimate for informational purposes. The due date provided by your doctor or midwife, especially one confirmed or adjusted after an ultrasound, should always be considered your official due date for all medical care and planning.