How Calculators Cloud Calculates

Three principles govern every calculator we build.

Source first. Before writing a single line of code, we identify the authoritative source for the formula. For financial calculations this is usually standard accounting convention or a named financial model. For health calculations it is a published clinical guideline or peer-reviewed equation. For unit conversions it is the International System of Units (SI) or an established conversion standard. The source is documented on each calculator page.

Implement exactly. We apply the formula as specified in the source, with no modifications that would alter the result. Where a source specifies rounding rules, we follow them. Where a source specifies the order of operations, we follow it. The goal is a result that matches what you would get if you worked through the formula by hand.

Test against known outputs. Every calculator is tested against published reference values before it goes live. For a compound interest calculator, that means testing against published amortization examples. For a BMI calculator, that means testing against WHO published reference cases. If the output does not match the reference, we do not publish until it does.

Business calculators

Business formulas follow standard accounting conventions as documented by established financial and accounting bodies. Profit margin, markup, break-even, and ROI formulas derive from fundamental accounting identities that are consistent across territories.

• Profit margin:net profit ÷ revenue × 100. Gross vs net distinction follows standard income statement definitions.
• Break-even:fixed costs ÷ (price per unit − variable cost per unit). Standard contribution margin formula.
• Markup:(selling price − cost) ÷ cost × 100. Distinguished from margin, which divides by revenue not cost.
• ROI:(return − cost) ÷ cost × 100. Annualised ROI uses the compound annual growth rate formula.

Finance calculators

Mortgage, loan, and amortization calculations use standard time-value-of-money formulas. These are documented in financial mathematics textbooks and used by every major lender's own calculation tools.

• Monthly payment:P × [r(1+r)ⁿ] ÷ [(1+r)ⁿ− 1], where P is principal, r is monthly rate, n is total payments.
• Compound interest: A = P(1 + r/n)^nt, where P is principal, r is annual rate, n is compounding periods per year, t is years.
• Amortization schedules:derived from the monthly payment formula, with each period's interest recalculated on the remaining balance.

Health calculators

Health formulas are sourced from published clinical guidelines and peer-reviewed equations.

• BMI:weight (kg) ÷ height (m)². Source: World Health Organization (WHO). Classification ranges follow WHO standard ranges.
• Calorie intake / TDEE: Mifflin–St Jeor equationfor basal metabolic rate × activity multiplier. Source: Mifflin MD et al., “A new predictive equation for resting energy expenditure in healthy individuals,” American Journal of Clinical Nutrition, 1990.
• Body fat percentage: US Navy method body fat formula. Source: Hodgdon and Beckett, Naval Health Research Center, 1984.
• Due date calculator: Naegele's rule (LMP + 280 days). Source: standard obstetric convention.
• Ideal weight: Devine formula (50 kg + 2.3 kg per inch over 5 feet for males; 45.5 kg for females). Source: Devine BJ, Drug Intelligence and Clinical Pharmacy, 1974.

Unit converters

Unit conversion factors are sourced from the International System of Units (SI) as published by the Bureau International des Poids et Mesures (BIPM), and from the US National Institute of Standards and Technology (NIST) for US customary units. Conversion accuracy is maintained to at least 6 significant figures. Results are displayed rounded to a practical precision for the unit type.

Tax calculators

Tax rates and brackets are sourced from official government publications and updated when legislative changes are announced. Tax calculators display the rate year and a note that results should be verified with a tax professional or official government calculator for final filing purposes.

Tax calculations are necessarily simplified. They apply standard rates without individual allowances, credits, deductions, or jurisdictional variations unless explicitly stated.

Construction and home calculators

Material estimation formulas follow industry standard methods as published by construction trade bodies and engineering references. Results include a standard waste factor where applicable. The waste factor used is stated on each calculator page.

Every calculator follows the same process from formula to published page.

1. Source identification. We identify the primary source for the formula. Peer-reviewed papers for health calculations. Financial mathematics references for finance. Official standards bodies for units and physical constants.
2. Formula verification. We cross-reference the formula against at least two independent sources. Where sources differ, we document the variation and use the most widely accepted version.
3. Implementation. The formula is implemented as a pure TypeScript function in our codebase. Pure functions take inputs and return outputs with no side effects. This makes them independently testable.
4. Unit testing. Every formula function is tested against a set of known reference outputs before integration. Tests cover standard cases, edge cases (zero values, negative inputs), and boundary conditions. A formula that does not pass its test suite is not published.
5. Review. Formula implementation and test results are reviewed before the calculator goes live.
6. Documentation.The source is documented on the calculator page in the “How it works” section. The formula is displayed in the open so users can verify the calculation themselves.

We do not invent formulas. If an established formula does not exist for a calculation, we do not build a calculator for it. Calculators Cloud does not produce original research or proprietary scoring systems.

We do not adjust outputs for commercial reasons. No partner, advertiser, or sponsor influences the result of any calculation. Results reflect the formula applied to your inputs, nothing else.

We do not guarantee results match your situation. The formulas are correct. Whether they perfectly model your specific lender, employer, jurisdiction, or medical circumstances is a separate question. See the Disclaimer for the full explanation.

Formulas can contain implementation errors. Tax rates and medical guidelines change. When either happens, we fix it.

If you find an error in any calculator — wrong result for a known input, formula that does not match the source, or outdated rate — email support@calculator-s.cloud with the calculator name and the specific discrepancy. We verify and correct within 48 hours in most cases.

Formula sources and the date each calculator was last reviewed are documented on each individual calculator page.

• Disclaimer — what our results can and cannot tell you
• About — who runs Calculators Cloud and why
• Contact — report an error or request a missing calculator