Due date calculator
An estimate. Only about one baby in twenty-five is born on its estimated due date; anything from 37 to 42 weeks is term.
The estimated due date is 40 weeks — 280 days — from the first day of the last menstrual period. Only about 4% of babies arrive on it; term is anywhere from 37 to 42 weeks, so a fortnight either side is entirely normal.
How to find your due date
Two milestones matter more than the due date itself. Twenty-four weeks is the legal threshold of viability in many countries and the point at which neonatal care changes substantially. Thirty-seven weeks is full term, after which birth is no longer considered premature. The due date sits at forty and functions mainly as a planning anchor and a reference point for monitoring — its precision is far lower than the specificity of a single named day suggests.
Questions
Forty weeks from the last period, but 37 to 42 weeks is all considered term.