Pregnancy Due Date Calculator — When Is Your Baby Due?
Calculate your estimated due date using Naegele's rule. Based on your last menstrual period (LMP).
How Is Due Date Calculated?
Naegele's rule — the standard method used by obstetricians — adds 280 days (40 weeks) to the first day of your last menstrual period. The formula: LMP + 280 days = estimated due date. Only about 5% of babies arrive exactly on their due date; most are born within two weeks before or after.
Pregnancy Trimesters
First trimester: weeks 1-13. Second trimester: weeks 14-27. Third trimester: weeks 28-40. Each trimester brings unique developmental milestones and maternal changes.
Frequently Asked Questions
How accurate is the due date?
Only about 5% of babies are born on their exact due date. Most arrive within two weeks before or after. The due date is an estimate based on a standard 280-day pregnancy.
What if I don't know my LMP date?
An early ultrasound (before 20 weeks) provides the most accurate dating. Some healthcare providers use the date of conception if known, adding 266 days instead of 280.
Can the due date change?
Yes. Your healthcare provider may adjust your due date based on ultrasound measurements, especially if the LMP-based date differs significantly from ultrasound dating.