bumpcalc.comPregnancy Due Date Calculator
Enter your last menstrual period (LMP) or conception date to estimate your due date and current pregnancy stage.
Select a date to see your due date estimate and milestones.
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Frequently Asked Questions
How accurate is the due date calculator?
This calculator uses Naegele's rule, the same formula used by OB-GYNs worldwide. Only about 5% of babies are born on their exact due date, but most arrive within 2 weeks of the estimate. Your doctor may adjust the date based on ultrasound findings.
How is my due date calculated?
Your due date is calculated by adding 280 days (40 weeks) to the first day of your last menstrual period (LMP), or 266 days (38 weeks) from your conception date. This is known as Naegele's rule and has been the standard obstetric method since the 19th century.
Can my due date change?
Yes. Your doctor may adjust your due date based on ultrasound measurements, especially if done in the first trimester. First-trimester ultrasound dating is generally more accurate than LMP-based calculations, particularly if your cycles are irregular.
What is Naegele's rule?
Naegele's rule is a standard method to estimate the due date of a pregnancy. It assumes a 28-day menstrual cycle and calculates the due date as 280 days (40 weeks) after the first day of the last menstrual period. It was named after German obstetrician Franz Karl Naegele (1778–1851).