This page explains how we build and check the calculators on this site.
How our calculators are built
Each calculator implements a standard, published formula. Where a field has multiple accepted formulas or conventions, we state which one we use and why.
Verification
New calculators are tested against worked examples with known answers before publication. We re-check tools when we change their logic.
Showing our work
Wherever it is helpful, we show the formula and the intermediate steps so that you can follow and verify the calculation yourself.
Corrections
If we discover an error, we fix it and, where the change is significant, note it on the affected page. To report an error, see our contact page.
Advertising independence
This site is funded by advertising. Advertisers have no influence over our calculators, formulas or content.