How does the calculator use last menstrual period?

When last menstrual period is selected, the calculator adds 280 calendar days to the entered date. It also uses that same entered date as the start date for trimester endpoints, full term date, and current week calculation shown in the results.

How does it use conception date?

When conception date is selected, the due date is the conception date plus 266 days. The calculator then sets its timeline start date as conception date plus 14 days, which affects the displayed current week, trimester dates, and full term date.

Can this replace an ultrasound due date?

No. A clinician may use early ultrasound, cycle history, embryo transfer information, physical findings, or other medical details to assign the official estimated due date. Use the provider's date for appointments, screening windows, medication timing, and medical decisions safely.

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Pregnancy

Pregnancy dates, growth, and related estimates.

Choose the tool whose inputs and output match your task. Check each calculator’s assumptions and limitations before using its result.

Latest update: Aug 14, 2026

Pregnancy tools estimate the dates that shape appointment timing and planning: due date, gestational age, conception, and reverse dating. The pregnancy due date calculator computes an expected due date from the first day of the last menstrual period (the 280-day convention) or from a conception date (266 days) and lays out trimester milestones. Reach for it when you know one of those dates and want a planning estimate — but treat the result as education, not a promise: due dates assume a typical cycle, early ultrasound may revise them, and your clinician assigns the working date. The reverse due date calculator works back from a target date, and the gestational age calculator finds the current week from a known start. See more planning tools in the Health collection.

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Pregnancy Due Date Calculator

Estimate pregnancy due date from last menstrual period or conception date, with current week and trimester timeline details.

Updated Aug 14, 2026

Verified Aug 14, 2026

Frequently asked questions

How does the calculator use last menstrual period?: When last menstrual period is selected, the calculator adds 280 calendar days to the entered date. It also uses that same entered date as the start date for trimester endpoints, full term date, and current week calculation shown in the results.
How does it use conception date?: When conception date is selected, the due date is the conception date plus 266 days. The calculator then sets its timeline start date as conception date plus 14 days, which affects the displayed current week, trimester dates, and full term date.
Can this replace an ultrasound due date?: No. A clinician may use early ultrasound, cycle history, embryo transfer information, physical findings, or other medical details to assign the official estimated due date. Use the provider's date for appointments, screening windows, medication timing, and medical decisions safely.