Pregnancy Due Date Calculator – Estimate Your Birth Date
Calculate your estimated due date and current pregnancy week from your last menstrual period. Includes trimester breakdown and key milestone dates.
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Naegele's Rule: How Due Dates Are Calculated
The standard due date calculation (Naegele's rule) adds 280 days (40 weeks) to the first day of your last menstrual period. This assumes a 28-day cycle and ovulation on day 14. Only about 5% of babies are born exactly on their due date; 80% are born within 2 weeks before or after.
Pregnancy Trimesters
First trimester (weeks 1–12): Organ formation, highest miscarriage risk, morning sickness common. Second trimester (weeks 13–26): Energy typically returns, baby begins moving, anatomy scan around week 20. Third trimester (weeks 27–40): Rapid weight gain, baby lung development, birth preparation.
Ultrasound vs LMP Dating
Early ultrasound (before 14 weeks) is more accurate than LMP-based calculation, especially for women with irregular cycles. If ultrasound shows a different gestational age than LMP dating, the due date is typically revised to match the ultrasound measurement.