Due Date Calculator
Estimate your due date (Naegele's rule, LMP + 280 days), current gestational age, and trimester. For reference—confirm with ultrasound. Everything runs in your browser.
Enter the first day of your last period
FAQ
Why count from the last period?
Ovulation is hard to pinpoint, so obstetrics counts from the last menstrual period as week 0. Conception typically happens ~2 weeks later.
Will the baby arrive on the due date?
Only ~5% of babies arrive on the exact date; 37–42 weeks is normal. Ultrasound dating adjusts for cycle length differences.
How are trimesters divided?
Here: 1st = weeks 0–13, 2nd = 14–27, 3rd = 28+. Definitions vary by a week or two between institutions.
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