Calculate pregnancy due date from last menstrual period
Built & maintained by Pappu Venkata Subbi Reddy, founder of Clacify · Formulas verified against official Indian government sources
Clacify's Pregnancy Due Date Calculator uses Naegele's Rule — the standard method used by obstetricians — to calculate your Estimated Due Date (EDD): add 280 days (40 weeks) to the first day of your Last Menstrual Period (LMP). The tool also shows your current pregnancy week, trimester, and milestone dates. Note that only 5% of babies are born exactly on the EDD; most births occur within 2 weeks before or after.
Naegele's Rule: add 280 days (40 weeks) to the first day of your last menstrual period. Alternatively, add 7 days and subtract 3 months. Example: LMP = 1 January 2026 → Due date = 8 October 2026. Clacify's Due Date Calculator does this automatically and shows your current week.
Due date calculators based on LMP assume a 28-day cycle with ovulation on day 14. If your cycle length differs, the actual due date may be off by a few days. Ultrasound dating (especially in the first trimester) is more accurate. Only 5% of babies are born on their EDD — 80% are born within 2 weeks of it.