How does this calculator work?

Estimated due date = last menstrual period + 280 days + (cycle length − 28 days).

Are calculator results guaranteed to be exact?

Results are estimates based on the inputs and formula used by the calculator. Review the assumptions and use professional advice where appropriate.

ONLINE CALCULATOR

Due Date Calculator

First day of last menstrual periodAverage cycle length (days)

ResultCalculated for the selected inputs

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What Is the Due Date Calculator?

A due date calculator estimates the expected delivery date from the first day of the last menstrual period and average menstrual-cycle length. It is designed specifically for estimating the expected date of delivery and comparing different dating assumptions. It does not replace clinical pregnancy dating.

How to Use the Due Date Calculator

Enter the values requested by the calculator.
Check the units and assumptions for each field.
Select Calculate to generate the result.
Change an input and calculate again if you want to compare scenarios.

Calculation Method

For a 28-day cycle, the standard estimate is 280 days from the first day of the last menstrual period; the estimate is adjusted by the difference between the entered cycle length and 28 days.

Example

Example: enter the values relevant to your Due Date Calculator scenario, calculate the result, and then change one input at a time to see how that specific variable affects the outcome.

Understanding the Result

The result is determined by the inputs required for Due Date Calculator, the units used, and the assumptions built into its calculation. Review each field before comparing results.

Tips and Notes

For a useful comparison, keep units consistent and test more than one realistic scenario. When the result affects an important financial, health, legal, or technical decision, verify key assumptions with an appropriate authoritative source.