Methodology and calculation standards

Deterministic formulas

Every calculator uses a documented, deterministic financial formula. The same inputs always produce the same outputs. There is no AI, no estimation service, and no server-side model involved in producing a result.

Each calculator page includes a “Formula” section showing the exact formula used, written out in plain notation, together with the assumptions applied.

Calculations happen in your browser

All normal calculations run locally in your browser using JavaScript. The financial values you enter are not uploaded to any server, stored in logs, sent to analytics, or shared with third parties.

If you explicitly create a share link, your inputs are encoded into that link's address so the recipient's browser can recreate the calculation — that is the only time your inputs leave the page, and only because you chose to copy them.

Results depend on your inputs

Calculators project outcomes from the values you enter and the stated assumptions. Real products differ: rates change, fees vary, lenders round differently, and tax rules evolve. Treat results as estimates for comparison and understanding, not as quotes or advice.

Country-specific rules are versioned

Where a calculator depends on country-specific rules (for example tax bands or transfer duties), the page states the country, the rule year, and the effective date of the configuration it uses. Rules are updated manually through a versioned configuration — we do not claim automatic, real-time regulatory updates.

Rounding

Calculations are performed at full floating-point precision and rounded only for display and export. Displayed columns can therefore differ from displayed totals by a small rounding amount. CSV exports use two decimal places.

Automated testing

Every formula is covered by automated unit tests, including reference cases verified by independent manual calculation, zero-rate cases, minimum and maximum values, rounding-sensitive cases, and invalid-input rejection. A calculator is not published until its tests pass.

Not financial advice

FinanceCalcWorks calculators are informational tools. They are not financial, tax, legal, or investment advice, and they do not consider your personal circumstances. For decisions that matter, verify the numbers with the actual provider and consider consulting a qualified professional.