Pregnancy Due Date Calculator

Reviewed by the CalculatorHub team, edited by James Graham. Method from NICHD Pregnancy. Last verified 2026-06-23.

The Pregnancy Due Date Calculator computes pregnancy due date from the relation days to due date = (LMP serial day + 280) - today serial day. It takes 6 inputs (last menstrual period year, last menstrual period month 1 to 12, last menstrual period day 1 to 31, today year, today month 1 to 12, today day 1 to 31) and returns the pregnancy due date. Because this is a pure mathematical or physical formula rather than a jurisdiction-specific rule, the result never changes over time: the same inputs always produce the same answer, so you can rely on it whether you are checking homework, sizing a design, or sanity-checking another tool. Enter your values in the fields below and the result updates instantly; you can also share a permalink that pre-fills the exact calculation, which is useful for teaching, reports, or collaboration. For example, with last menstrual period year = 2026, last menstrual period month 1 to 12 = 1, last menstrual period day 1 to 31 = 1, today year = 2026, today month 1 to 12 = 1, today day 1 to 31 = 1, the pregnancy due date works out to 280, and the worked example further down the page shows every step so you can follow the arithmetic and reproduce it by hand. The method is the standard form documented by NICHD Pregnancy, and the figure above each result carries the date it was last verified. This tool is general information and is not a substitute for professional engineering, medical, financial, or scientific advice; always check critical results against the primary source and your own judgement.