Como funciona a Pregnancy Due Date Calculator
The calculation uses Naegele's Rule, the medical standard since 1812: the estimated due date (EDD) is 280 days (40 weeks) after the first day of your last menstrual period (LMP). If your cycle length differs from 28 days, the difference is added or subtracted.
Formula: EDD = LMP + 280 + (cycle length − 28) days. Gestational age is counted from day 1 of your last period: week = ⌊days since LMP ÷ 7⌋ + 1. Trimesters: weeks 1–13 = first trimester, weeks 14–27 = second trimester, week 28+ = third trimester.