Our Methodology

This page explains how CalcAuthority builds, documents, and maintains its calculator tools. Transparency about methods is a core principle: if you cannot see how a result was calculated, you cannot judge whether it applies to your situation.

Formula Selection

Where a standard, widely accepted formula exists — such as the amortization formula for loans and mortgages, or the percentage change formula — we use it exactly as established. We do not approximate or substitute proprietary methods. The formula is stated on each calculator page in plain language so any user can reproduce the calculation by hand.

For estimates with no single authoritative formula (such as take-home pay, which depends on individual tax variables), we use a simplified model, state the simplification explicitly, and note what is not included in the estimate.

Stated Assumptions

Every calculation involves assumptions. CalcAuthority states these directly on each calculator page rather than burying them in footnotes. Common examples:

  • Salary-to-hourly conversions assume a user-specified number of hours and weeks. The default (40 hours × 52 weeks) is stated, not silently applied.
  • Loan and mortgage calculations assume fixed interest rates and equal monthly payments. Variable-rate loans are not modeled.
  • Take-home pay estimates use a single combined effective deduction rate supplied by the user. They do not apply a tax-table calculation, which would require personal filing information.
  • Gas cost calculations use the MPG figure entered by the user, which may differ from the EPA sticker.

Worked Examples

Every calculator includes at least two worked numeric examples. These serve two purposes: they demonstrate the formula in action with real numbers, and they allow any user to verify that the calculator is functioning correctly by checking a known input/output pair. If the calculator and the worked example produce different results for the same inputs, that is a signal to investigate — please use the contact page to report it.

Limitations of Each Estimate

Each calculator page includes a disclaimer section that specifies what the estimate does not include. For example:

  • Mortgage calculator results do not include property tax, insurance, PMI, or HOA fees.
  • Take-home pay results do not account for state-specific tax rules, multiple income sources, or complex deduction scenarios.
  • Loan payment results do not include origination fees, prepayment penalties, or other lender charges.

Stating these limitations is not a legal disclaimer only — it is essential for the estimate to be useful. A number without its limitations is easy to misapply.

Review and Accuracy

Formulas are verified against reference sources (textbooks, government publications, or established financial standards) and cross-checked with worked examples before publication. Calculator logic is tested against the worked examples shown on each page. If you find a discrepancy between a calculator's output and its stated worked example, please report it via the Contact page.

We update pages when regulatory thresholds, tax rates, or standard figures change materially — for example, FICA rates or FLSA overtime thresholds. If you notice outdated information, contact us.

What Our Calculators Are Not

CalcAuthority calculators are educational tools. They are not:

  • Financial advice
  • Tax advice or tax preparation tools
  • Mortgage or lending applications
  • Legal advice
  • Personalized professional recommendations

See our Financial Disclaimer for the full statement. For decisions that depend on accurate financial, tax, or legal outcomes, consult a qualified professional.