How We Build and Check Our Calculators

Money decisions deserve numbers you can trust. This page explains exactly how every calculator on Clear Money Math is built and checked, so you can judge the results for yourself.

1. Standard, published formulas

Our calculators use the standard formulas of personal finance: loan amortization, compound growth, the Fisher relation between nominal returns, inflation and real returns, and the safe-withdrawal-rate framework from retirement research. Every calculator page shows its formula and a worked example, so you can reproduce the result with a spreadsheet or a pocket calculator.

2. Automated tests against known values

Each formula is covered by automated tests that run every time the site is updated. The tests check results against independently known values. For example, a 30-year $200,000 loan at 6% must produce a $1,199.10 monthly payment, and payoff times must match closed-form formulas. If a test fails, the update is not published.

3. Authoritative sources

Facts and rules of thumb (such as the 4% withdrawal rate, credit card rate levels, or how lenders evaluate debt-to-income ratios) are checked against primary sources: U.S. government agencies like the Consumer Financial Protection Bureau, the Federal Reserve, the IRS and the Bureau of Labor Statistics, lender guidelines, and peer-reviewed or professional research. Each calculator lists its sources at the bottom of the page.

4. Human review

Every calculator and article is reviewed by our editor, Patrick Legallais, before publication and again whenever it is updated. The "Updated" date on each page shows the last review. Software tools, including AI assistants, help us write code and drafts, but nothing is published without passing the tests above and a human review.

5. Transparent limitations

Calculators simplify reality. Markets don't deliver steady average returns, lenders apply their own rules, and taxes depend on your situation. Each page explains the main assumptions and limitations of its calculator. Results are estimates for education and planning, not financial, tax or legal advice.

6. Independence

Clear Money Math is funded by advertising, and in the future may earn commissions from clearly labeled partner links. Advertising and partnerships never change how a calculator works or what result it shows. Any partner link will be disclosed on the page where it appears.

Found an error?

Tell us at hello@clearmoneymath.com with the page, the numbers you entered and the result you expected. We review every report and correct confirmed errors promptly.