Calculator

Pregnancy Due Date Calculator

Estimate due date, gestational age, and trimester from LMP.

Last updated: August 21, 2026

How it works

Method

The due date estimate uses the common last-menstrual-period method: add 280 days, or 40 weeks, to the first day of the last period.

Assumptions

Due-date estimates from LMP are approximate. A clinician may adjust dating after ultrasound or clinical review.

Limitations

This estimate is informational and should not replace prenatal care, ultrasound dating, or advice from an obstetric clinician.

References

ACOG: Methods for Estimating the Due Date ACOG: When Pregnancy Goes Past Your Due Date

FAQ

How is the due date calculated?

The common LMP method adds 280 days, or 40 weeks, to the first day of the last menstrual period.

Can an ultrasound change the due date?

A clinician may use ultrasound and clinical context to confirm or revise pregnancy dating.

Is the due date guaranteed?

No. It is an estimate used for planning prenatal care and tracking pregnancy progress.

Should I rely on this instead of a doctor?

No. Use this as a planning estimate and confirm dates with an obstetric clinician.