Due Date Calculator
Estimate a pregnancy due date from the first day of the last menstrual period or a known conception date, with gestational timing shown as an estimate.
About This Tool
Adds 280 days to the first day of the last menstrual period, or 266 days to a known conception date. Conception mode subtracts 14 days when displaying conventional gestational age.
People seeking a general pregnancy dating estimate. It does not confirm pregnancy, fetal development, viability or the timing of labour.
All calculations happen entirely in your browser. No dates or health data is transmitted or stored. ToolBullet never collects your health data.
How pregnancy dating is estimated
Standard gestational dating counts from the first day of the last menstrual period, about 280 days before the estimated due date. A conception-date estimate adds 266 days, while conventional gestational age is still displayed from an assumed date 14 days before conception.
Trimester labels begin at 14 and 28 completed weeks. Term categories are not all the same: 37–38 weeks and 6 days is early term, while 39–40 weeks and 6 days is full term.
Authoritative references
Reviewed 23 June 2026: ACOG: methods for estimating the due date; ACOG: definition of term pregnancy; World Health Organization: maternal health.