Editorial Policy & Methodology
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People use our calculators to make real decisions about money. This page explains how we build, verify and update them.
Sources we use
We rely on primary, official sources wherever possible:
- United States: Internal Revenue Service (IRS) revenue procedures and notices, Social Security Administration, state departments of revenue, Bureau of Labor Statistics (BLS), Federal Reserve Bank of St. Louis (FRED), Freddie Mac Primary Mortgage Market Survey, U.S. Energy Information Administration (EIA), Department of Transportation.
- Canada: Canada Revenue Agency (CRA) payroll formulas (T4127) and tables (T4032), Revenu Québec, Retraite Québec, provincial finance ministries, Bank of Canada, Canada Mortgage and Housing Corporation (CMHC), Canadian Transportation Agency.
- International: European Central Bank euro reference rates.
Where we use a reputable secondary compilation (for example, the Tax Foundation's state tax tables), we cross-check key figures against the original government source.
How a calculator is built
- We document the official formula and every assumption.
- We implement the calculation and test it against worked examples published by the government or against official calculators.
- We write a plain-English explanation of how the result is calculated, including what the calculator does not account for.
- Every calculator lists its sources and its "last updated" date.
How we keep calculators current
- Automatic updates: market data (mortgage averages, central bank rates, exchange rates, CPI inflation, fuel prices) is refreshed automatically several times a day or week.
- Scheduled reviews: tax tables and contribution limits are reviewed every year as soon as new figures are published, and whenever a federal, state or provincial budget changes them.
- Reader corrections: if you find an error, tell us. We investigate every report and correct confirmed errors promptly.
Independence
Advertising pays for this site, but advertisers have no input into our tools or articles. We do not accept payment to change results or rankings.
Limitations
Calculators simplify complex rules. Results are estimates and may differ from your actual tax return, pay stub, loan offer or benefit amount. See our Disclaimer.