How We Calculate
Our approach to formula accuracy, data sourcing, and keeping results up to date.
Our Philosophy
Every calculator on TrueTools.org is designed to produce the same result you would get from a CPA, financial planner, or clinical reference table — not an approximation. We build our math as pure, testable functions in a central library (formulas.js) and run an automated test suite against known-good reference values before each release.
Tools are educational. They help you understand your numbers, explore scenarios, and prepare for conversations with licensed professionals. They are not a substitute for professional financial, tax, medical, or legal advice.
Data Sources
We source data exclusively from official government agencies, international bodies, and peer-reviewed standards. The specific sources for each category are:
US Tax & Finance
- Income tax brackets and standard deductions: IRS Revenue Procedures (annual inflation adjustments)
- Social Security & Medicare rates: Social Security Administration OACT
- 401(k) contribution limits: IRS Retirement Topics
- HSA limits: IRS Revenue Procedure (annual HDHP announcement)
- Capital gains rates and estate tax thresholds: IRS Topic 409
- State sales tax rates: State Department of Revenue official rate schedules
Canadian Tax
- Federal and provincial brackets: Canada Revenue Agency
- CPP & EI rates: CRA Payroll Deductions
- RRSP & TFSA limits: CRA RRSP contributions
UK Tax
- Income tax bands and Personal Allowance: HMRC Income Tax rates
- National Insurance rates: HMRC NI rates
- Stamp Duty Land Tax: HMRC SDLT guidance
Australian Tax
- Income tax rates: Australian Taxation Office
- Medicare Levy: ATO Medicare Levy
- Superannuation rate: ATO Super Guarantee
Health
- BMI formula and weight categories: World Health Organization
- Calorie requirements (Mifflin-St Jeor equation): Mifflin et al., Journal of the American Dietetic Association (1990)
- Body fat percentage methods: U.S. Navy circumference method and American Council on Exercise reference ranges
- Daily water intake: National Academies of Sciences Dietary Reference Intakes (DRI)
- A1C to eAG conversion: American Diabetes Association formula
Formula Accuracy
All calculation logic lives in formulas.js — a pure, side-effect-free JavaScript library. Each exported function takes numbers in and returns numbers out, with no DOM access. This separation means we can unit-test every formula in isolation.
We maintain an automated test suite with over 400 tests covering known-good reference values. Before any update is released, all tests must pass. If a test reveals a discrepancy with an official source, the formula is corrected and the source is updated in the test file with a citation to the authoritative document.
Update Schedule
Tax and financial constants (brackets, limits, rates) are reviewed and updated every October when the IRS and equivalent agencies publish annual inflation adjustments. UK, Canadian, and Australian tools are updated when budgets are announced or confirmed by the respective government agency. Health and mathematical tools are reviewed annually or when a relevant clinical guideline is updated.
Each page displays a "Last reviewed" date in the page header so you can see exactly when the information was last verified.
Our Review Process
Shalini Pathak (Senior Account Officer, M.A. Finance & Accounting) reviews all finance, tax, and business calculators for formula correctness, appropriate caveats, and alignment with current regulations. Health and medical tools are reviewed against the cited clinical sources for accuracy of reference values and interpretation guidance.
Santosh Timilsina (Founder, TrueTools.org) is responsible for the underlying software implementation, automated test coverage, and annual data updates.
Disclaimer
Results from TrueTools.org calculators are for educational and informational purposes only. They do not constitute financial, tax, medical, legal, or investment advice. Tax laws and benefit rules change frequently — always verify the current rules with the relevant government agency or consult a qualified professional before making decisions based on these calculations.
Questions about a specific tool's sources? Contact us and we'll provide the exact reference.