How is the due date calculated?

This tool uses the Naegele rule: due date = first day of last menstrual period (LMP) + 280 days.

Is the due date exact?

No. The date is an estimate. Many babies are born within a week or two. Your care team may refine it with early ultrasound.

Pregnancy Due Date (Naegele)

Estimated due date from last menstrual period (LMP + 280 days).

What this calculator does

This tool estimates your baby’s due date from the first day of your last menstrual period (LMP), using the Naegele rule (LMP plus 280 days).

What your result means

The date is an estimate. Many babies are born within a week or two of this date. Your care team will use it for planning and monitoring. Early ultrasound may be used to refine the date.

This is not medical advice. A healthcare provider should interpret results in your context.

Last menstrual period

Key terms

LMP: Last menstrual period; the first day of the last period before pregnancy.
Naegele rule: A common method: due date = LMP + 280 days (or LMP + 1 year − 3 months + 7 days).
EDD: Estimated date of delivery (due date).
Gestational age: How far along the pregnancy is, usually in weeks and days from LMP or from ultrasound.

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This tool is for educational and reference use only. It does not constitute medical advice. Always consult a healthcare professional for medical decisions.