Calculator

Pregnancy Due Date Calculator

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

Last updated: August 21, 2026

Private by design Inputs are calculated in this browser.
Educational estimate This tool does not diagnose or replace clinical care.
Use measured inputs Accurate dates and measurements improve the estimate.
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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.

How to use the Pregnancy Due Date Calculator

Use this health calculators tool by entering the requested information, reviewing the result, and adjusting your inputs when you need to compare another option. ToolsMagicPro processes the information needed for the selected task and presents a practical result you can copy, download, or use in your next step.

For the most reliable outcome, check that names, numbers, files, URLs, or settings are complete before you run the tool. Results are intended to help with everyday research and workflow decisions. Where a result affects an important financial, legal, health, security, or publishing decision, confirm it with the relevant official source or qualified professional. You can also explore the related tools above to continue the same workflow without starting from scratch.