How to Check If a Calculator Answer Is Reasonable

Calculators are only as good as the inputs you give them. A single misplaced decimal can turn a mortgage payment or BMI result from plausible to absurd. Ask: should this answer be bigger or smaller than what I started with? - A percentage of a large number should not be tiny unle

Published June 8, 2026

Calculators are only as good as the inputs you give them. A single misplaced decimal can turn a mortgage payment or BMI result from plausible to absurd.

Does the magnitude make sense?

Ask: should this answer be bigger or smaller than what I started with?

A percentage of a large number should not be tiny unless the rate is tiny
BMI for an adult should usually fall between 15 and 40
A monthly loan payment should not exceed the loan amount

Unit checklist

Why did my BMI look wrong?: Height might be in feet while the tool expects centimeters.
Why is my percentage over 100%?: Sometimes that is correct (growth), sometimes the rate was entered as 0.20 instead of 20.