Health calculator

Pregnancy Due Date Calculator

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

FormulaEstimated due date = LMP + 280 days

Formula

Due date estimate

Due dates are estimates. Ask a qualified clinician for pregnancy dating and medical decisions.

Estimated due date = LMP + 280 days

A last menstrual period on 1 January gives an estimated due date around 8 October.

FAQ5 common questions for this calculator.

FAQs

How is the due date estimated?+

A common estimate adds 280 days to the first day of the last menstrual period.

How does the Pregnancy Due Date Calculator calculate the result?+

For the Pregnancy Due Date Calculator, it uses the Due date estimate: Estimated due date = LMP + 280 days. A last menstrual period on 1 January gives an estimated due date around 8 October.

What information do I need to use the Pregnancy Due Date Calculator?+

For the Pregnancy Due Date Calculator, enter first day of the last menstrual period. Keep the units consistent with the calculator fields and compare your setup with the worked example on the page.

How accurate is the Pregnancy Due Date Calculator?+

Pregnancy Due Date Calculator is only as accurate as the first day of the last menstrual period entered. It applies the Due date estimate shown on this page, then rounds for readability. Treat the output as screening guidance rather than a diagnosis.

What should I check before using the Pregnancy Due Date Calculator result?+

For the Pregnancy Due Date Calculator, check first day of the last menstrual period, unit choices, and whether the calculator's assumptions fit the person being assessed. Use the result as screening or planning context, not as a diagnosis.

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Health guide

How to use the Pregnancy Due Date Calculator

Estimate a pregnancy due date from the first day of the last menstrual period. The page also explains the due date estimate and shows a practical example: A last menstrual period on 1 January gives an estimated due date around 8 October.

  1. 1

    Enter your details

    Enter the first day of the last menstrual period, then complete any other fields shown in the calculator.

  2. 2

    Check the calculation

    Review the result alongside the due date estimate: Estimated due date = LMP + 280 days.

  3. 3

    Compare scenarios

    Change one or more inputs to see how they affect the pregnancy Due Date Calculator result before you use the estimate.