How Due Dates Are Calculated
Calculation Example
Here's a practical example using the Pregnancy Due Date Calculator: Enter your values in the fields above to get instant results. Try adjusting the parameters to compare different scenarios. This tool helps you make informed decisions by providing accurate pregnancy due date calculations based on standard formulas and up-to-date data.
Frequently Asked Questions
How is the due date calculated?
Using Naegele’s rule: add 280 days to the first day of your last menstrual period, or 266 days from the conception date.
How accurate is a due date calculator?
Only about 5% of babies are born on the exact due date. Most arrive within 1–2 weeks before or after.
What are the three trimesters?
First: weeks 1–12. Second: weeks 13–27. Third: weeks 28–40. Each has distinct milestones.
Can my due date change?
Yes. An early ultrasound can adjust the due date if fetal measurements differ from the LMP estimate by more than a week.
When should I see a doctor?
Schedule your first prenatal appointment around week 8. Contact your doctor sooner if you experience bleeding or pain.