How does this calculator work?

The standard estimate is 280 days from the first day of the last menstrual period, adjusted for cycle length.

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

Pregnancy Calculator

First day of last menstrual periodAverage cycle length (days)

ResultCalculated for the selected inputs

—

What Is the Pregnancy Calculator?

A pregnancy calculator estimates an expected due date and pregnancy timing from the first day of the last menstrual period and average cycle length. Use it to estimate key pregnancy dates and understand approximately how far along a pregnancy may be based on the dates entered. It is an estimate and an ultrasound or clinician assessment may provide a different dating estimate.

How to Use the Pregnancy 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

Estimated due date = first day of the last menstrual period + 280 days, adjusted for a cycle length different from 28 days.

Example

Example: enter the values relevant to your Pregnancy 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 Pregnancy 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.