Pregnancy Due Date Calculator

Estimate pregnancy due date from the first day of the last menstrual period.

Enter your details and select Calculate.

This tool provides an estimate. Verify results before making financial, educational or medical decisions.

Pregnancy due date estimates

This guide explains how to use the calculator, includes an example, discusses limitations and answers common questions.

A due date is an estimate, not a guaranteed delivery date. Pregnancy dating often begins from the first day of the last menstrual period.

How to use this calculator

Enter the requested last menstrual period or other dating information. A common initial estimate adds 280 days (40 weeks) to the first day of the last period.

Worked example

If the first day of the last period was 1 January, a simple 280-day estimate places the due date around early October, depending on the year.

When this calculator is useful

Useful for understanding an approximate pregnancy timeline and preparing questions for antenatal appointments.

When not to rely on it

Cycles vary and conception timing is uncertain. Ultrasound dating and clinical assessment may revise the estimated due date. This tool cannot assess pregnancy health.

Practical tip

Use the date confirmed by your maternity team for clinical decisions and appointments.

Frequently asked questions

Will my baby arrive on the due date?

Not necessarily. Many births occur before or after the estimated date.

Is a 28-day cycle assumed?

Many simple methods assume a typical cycle; different cycles can shift estimates.

Can this replace an ultrasound?

No. Clinical dating and assessment are more appropriate for care decisions.

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Educational information only. Results are estimates unless otherwise stated. Verify important financial, medical or legal decisions with a qualified professional.