Pregnancy Due Date Calculator
Estimate your due date and current week of pregnancy
Frequently Asked Questions
This calculator uses Naegele's rule: your due date is your last menstrual period (LMP) plus 280 days (40 weeks), assuming a typical 28-day cycle. It's the same method most doctors use for an initial estimate.
Only about 4-5% of babies arrive on their exact due date — it's a statistical estimate, not a guarantee. A full-term pregnancy is considered anywhere from 37 to 42 weeks. An ultrasound in the first trimester typically refines the estimate.
Naegele's rule assumes a 28-day cycle with ovulation on day 14. If your cycles are longer or shorter, your actual due date may differ — an early ultrasound is the most reliable way to date the pregnancy in that case.
Pregnancy is dated from the first day of your last period, not from conception, which is why you're already considered about 2 weeks pregnant around the time you actually ovulate and conceive.
How this is calculated
Due date = first day of last period + 280 days, adjusted for cycle lengths other than 28 days. Conception is estimated at cycle length minus 14 days after your last period began.