Estimate a due date and calendar-based gestational age from either the last menstrual period or an estimated conception date.
Estimated Due Date
How Pregnancy Dating Is Estimated
Choose the date you know. When using the last menstrual period (LMP), the calculator adds 280 days to estimate the due date. When using a conception date, it adds 266 days. For gestational-age display, conception-based dating estimates the LMP as approximately 14 days earlier.
Clinical dating may differ
These calendar rules assume typical timing and do not account for every cycle pattern. A clinician may adjust dates using menstrual history, ultrasound, or other clinical information. The displayed trimester and week count are date-based estimates only.
Health note: This calculator does not confirm pregnancy or assess maternal or fetal health. Use prenatal care for diagnosis, dating, and decisions about care.
Source and important context
The American College of Obstetricians and Gynecologists notes that ultrasound may confirm or revise a last-menstrual-period estimate. This page provides a calendar estimate, not clinical pregnancy dating. ACOG: Methods for Estimating the Due Date. This page provides general educational estimates and is not a diagnosis or a substitute for individualized care. Page information updated: 4 November 2026.