Editorial Policy and Methodology

People use our calculators to make real decisions about money, health and their homes. This page explains how we build them, where the formulas and figures come from, and how we keep them accurate.

Our standards

Published methods only. Every calculator uses an established formula from a primary or widely recognized source, and names it on the page.
Show the working. Each tool includes the formula, a worked example with real numbers, and the assumptions behind the result.
Independence. Advertising pays for the site, but advertisers never influence our content, results or recommendations. We do not accept paid placements in calculators.
Plain English. We explain terms such as APR, amortization and marginal tax rate where they are used.

Sources we rely on

Tax and payroll: Internal Revenue Service revenue procedures and publications, and Social Security Administration announcements for wage base limits. Tax figures are updated when the IRS publishes the next year's inflation adjustments.
Loans and mortgages: the standard amortization formula used by US lenders, and consumer guidance from the Consumer Financial Protection Bureau.
Health: formulas from peer-reviewed research and public-health agencies, including the Mifflin-St Jeor equation, CDC and WHO adult BMI categories and the US Navy body fat method.
Units and dates: internationally defined conversion factors (for example, 1 inch = 2.54 cm exactly) and Gregorian calendar rules.

How we test

Before a calculator is published, we check its results against hand-worked examples and independent reference values, including edge cases such as zero interest rates, leap years and very large inputs. Every worked example on the site is generated from the same code that powers the calculator, so the text and the tool agree.

Reviews and updates

Each calculator shows the month it was last reviewed. Pages that depend on figures that change, such as tax brackets and contribution limits, are reviewed at least once a year and whenever official figures change.

Limitations

Calculators give estimates based on the inputs and assumptions shown. They are not financial, tax, legal or medical advice. For decisions with significant consequences, confirm the numbers with a qualified professional.

Corrections

If you find an error, please tell us through the contact page or at [email protected]. We review every report and correct confirmed errors promptly.