Due Date Calculator
Enter the first day of the last menstrual period (LMP) to calculate the EDD by Naegele’s rule.
Enter the LMP to calculate the due date.
How dating works
Naegele’s rule assumes a 28-day cycle with ovulation around day 14 — gestational age is counted from the LMP, not conception. Only about 1 in 20 babies arrives on the EDD; term spans weeks 37 through 42.
First-trimester ultrasound is the most accurate dating method and supersedes LMP dating when they disagree significantly — the provider establishes the official EDD.
Educational use only. Pregnancy dating is established and adjusted by the provider, often using first-trimester ultrasound; this calculator supports learning and estimation only. This material supports nursing education and exam review. It is not medical advice and is not a substitute for clinical judgment, institutional policy, or medical direction. Always follow facility protocols and current provider orders.