Estimated due date from last menstrual period (Naegele).
These calculators use established formulas (such as Mifflin-St Jeor for calorie needs or the Devine formula for ideal weight) to provide general estimates. They're built for a general population and don't account for individual medical conditions, medications, or circumstances. They aren't a substitute for advice from a doctor, registered dietitian, or other qualified healthcare provider — especially for anything related to pregnancy, chronic conditions, or medication dosing.
Naegele's rule adds 280 days (40 weeks) to the first day of your last menstrual period.
About 4% of babies arrive on the exact predicted date — most within a 2-week window on either side.
This method assumes a standard 28-day cycle with ovulation on day 14 — it's a widely used starting estimate, but an early ultrasound dating scan is what clinicians rely on for a more precise date.
LMP on January 1 → estimated due date around October 8 of the same year (280 days later).
Accurate for regular 28-day cycles. First-trimester ultrasound is more accurate and used to confirm.
Add extra days. A 32-day cycle usually ovulates on day 18, shifting the due date about 4 days later.
37 to 42 weeks. 39–40 is optimal.
Ultrasound measurements, especially in the first trimester, are generally considered more reliable than calendar-based estimates and often become the date of record once confirmed.