Due Date Calculator
Estimate your baby’s due date from the first day of your last menstrual period (LMP) using Naegele’s rule: LMP + 280 days. Also calculates current week of pregnancy.
Inputs
About Due Date Calculator
Naegele’s rule
Developed in the 1800s: due date = first day of LMP + 1 year − 3 months + 7 days = LMP + 280 days = ~40 weeks. Based on average 28-day cycles with ovulation at day 14. Most pregnancies actually deliver within 2 weeks of this estimate.
Accuracy
Only about 5% of babies arrive exactly on the due date. Most arrive within a 5-week window (week 37 to week 42). Ultrasound dating in the first trimester is more accurate than LMP for irregular cycles.
For irregular cycles
If your cycle isn’t 28 days, adjust by the difference. Cycle 30 days → add 2 days to the calculated due date. Cycle 26 days → subtract 2 days. Or rely on first-trimester ultrasound dating.