Calculator Accuracy Policy

How we build, verify, and maintain accurate calculators — and what to do when you find an error.

Last Updated: July 4, 2026

Our Commitment to Accuracy

Every calculator on FreebieCalculator.com is built to produce results that are mathematically correct and practically useful. We believe that a free online calculator has a responsibility to be as accurate as any paid software tool — and we take that responsibility seriously.

However, no calculator can perfectly account for every real-world situation. For decisions involving health, finance, taxes, or legal matters, our calculators provide estimates and educational context. We always recommend consulting a qualified professional for important personal decisions.

How We Build Our Calculators

1. Formula Research and Sourcing

Every calculator begins with research. We identify the standard formulas used by authoritative sources — including government agencies (IRS, CDC, WHO), academic institutions, and professional organizations (CFA Institute, American Heart Association). We document the source of every formula we implement.

2. Formula Verification

Before any calculator is published, we verify its formula against at least two independent sources. For financial calculators, we cross-check with bank or government publications. For health calculators, we reference peer-reviewed medical literature. For math calculators, we verify against established mathematical definitions.

3. Manual Test Cases

We create a set of manual test cases — inputs where the correct output is known — and run them through each calculator before publication. We include edge cases (zero values, maximum values, negative inputs where relevant) to ensure the calculator handles all scenarios correctly.

4. Cross-Calculator Verification

Where possible, we cross-check our results against reputable external calculators (government websites, established financial institutions) using the same inputs. Any significant discrepancy triggers a full formula review.

Data Sources We Use

The following is a non-exhaustive list of the types of sources we rely on for calculator data:

  • Tax rates: IRS official publications, state revenue department websites
  • Health formulas: World Health Organization (WHO), CDC, National Institutes of Health (NIH), peer-reviewed journals
  • Financial formulas: Consumer Financial Protection Bureau (CFPB), Federal Reserve publications, standard actuarial and financial mathematics
  • Mathematical formulas: Standard mathematical definitions as published in academic textbooks
  • Exchange rates: Live data from financial data providers (subject to delay)
  • Canadian tax rates: Canada Revenue Agency (CRA) official publications

For a full bibliography organized by calculator, see our Sources & References page.

Known Limitations

We are transparent about what our calculators cannot do:

  • Tax calculators use current-year rates but cannot account for all deductions, credits, AMT, or state-specific rules. Results are estimates only.
  • Health calculators use population-average formulas (like Mifflin-St Jeor or WHO BMI thresholds) that may not reflect individual variation due to genetics, medications, or medical conditions.
  • Currency converters use rates that may be delayed by 15–60 minutes and do not reflect bank or exchange service fees.
  • Investment calculators use assumed rates of return. Past market performance does not guarantee future results.
  • Retirement calculators cannot predict Social Security policy changes, healthcare cost inflation, or market volatility.

Our Review and Update Process

We review each calculator when:

  • Underlying data changes (e.g., new IRS tax brackets each January)
  • A user or reader reports a potential error
  • A referenced source updates its published formula or thresholds
  • Scheduled annual reviews for high-use financial and health calculators

When a calculator is updated, we note the update date on the calculator page itself. Major formula changes are also logged in our Update Log.

What to Do If You Find an Error

We genuinely appreciate error reports from our users — they help us maintain quality for everyone. If you believe a calculator is producing incorrect results:

  1. Note the calculator name, the inputs you used, the output you received, and the expected output.
  2. Include a reference source if you have one (e.g., a link to an authoritative calculation).
  3. Email us at bugs@freebiecalculator.com with this information.

We review all error reports within 48 hours and respond within 5 business days with either a correction or an explanation of the calculation methodology.

Disclaimer

FreebieCalculator.com calculators are provided for educational and informational purposes only. While we make every effort to ensure accuracy, we cannot guarantee that every result is correct in every circumstance. Our results should not be used as the sole basis for health, financial, legal, or other important personal decisions.

For binding or high-stakes decisions, please consult a qualified professional: a licensed physician for medical matters, a certified financial planner or CPA for financial and tax matters, and a licensed attorney for legal matters.