Due Date Calculator
Estimate your pregnancy due date and current week of pregnancy.
Updated
How Due Dates Are Calculated
Due dates are estimated by adding 280 days (40 weeks) to the first day of the last menstrual period (LMP), or 266 days (38 weeks) from the conception date. This is known as Naegele's rule.
Only about 5% of babies are born on their exact due date. Most births occur within two weeks before or after the estimated date. This calculator provides an estimate — your healthcare provider may adjust based on ultrasound measurements.
Frequently Asked Questions
How is my due date calculated?
Using Naegele's rule: 280 days (40 weeks) from the first day of your last menstrual period, or 266 days from conception if you know that date instead.
How accurate are due dates?
Only about 5% of babies arrive on their exact due date; most are born within two weeks either side. A first-trimester ultrasound gives the most accurate dating.
What if my cycles are longer or shorter than 28 days?
Naegele's rule assumes a 28-day cycle with ovulation on day 14. If your cycles differ, the estimate shifts — your care provider can adjust it, often using ultrasound.
Can my due date change during pregnancy?
Yes. If an early ultrasound measurement disagrees with the menstrual-period estimate by more than about a week, providers typically re-date the pregnancy to match the ultrasound.