About CalcBox

Who we are

CalcBox is built and maintained by a small team of independent web developers and content editors based in Brazil, writing for an international English-speaking audience. The project began in 2024 as an internal tool for verifying everyday financial and health calculations and grew into a public reference after readers asked for a single source they could trust for the formulas behind common decisions.

We are not a financial-services company, a medical provider, or a legal advisor. We do not sell user data, push affiliate products, or accept payment to feature specific tools. The site is funded entirely by display advertising served through standard ad networks, which lets every calculator stay free to use.

What we cover

CalcBox currently publishes more than 20 calculators across four categories, with new tools and accompanying blog explainers added regularly.

• Finance — mortgage, personal loan, compound and simple interest, savings goal, retirement planner, currency conversion, U.S. income-tax estimate.
• Health — Body Mass Index (BMI), Basal Metabolic Rate (BMR), body-fat percentage, daily water intake, running pace, Karvonen target-heart-rate zones.
• Math — percentages, percentage change, fractions, tips, discounts, sales tax, rule of three, area and volume of common shapes.
• Conversions — length, weight and temperature across the metric, U.S. customary and imperial systems.

Our methodology

Every calculator follows the same four-step process before it goes live:

1. Source the formula from a primary authority — peer-reviewed publications, official standards bodies (WHO, NIST, U.S. Treasury), or canonical textbooks. We never copy a formula from another calculator site.
2. Implement and unit-test the math in TypeScript with a suite of automated tests that compare our output against known reference values (for example, our compound-interest implementation is validated against worked examples from finance textbooks).
3. Write the explainer — every calculator ships with a 'How it works' section, a complete guide with at least one worked numerical example, and an FAQ that addresses the questions readers actually send us.
4. Manual review by a second team member before publishing, focused on edge cases (zero values, negative inputs, extreme ranges) and on plain-language clarity.

All math runs locally in your browser. Nothing you type is ever uploaded to our servers, logged, or shared with third parties.

Sources we rely on

We cite the underlying authority for each category rather than for each calculator, because the same standards are reused across multiple tools.

• Finance: standard amortization formulas as taught in introductory corporate-finance textbooks (Brealey, Myers & Allen; Bodie, Kane & Marcus); U.S. federal tax brackets published annually by the IRS; U.S. Treasury rate publications for the short-term simple-interest reference.
• Health: BMI cut-offs and interpretation from the World Health Organization (Obesity: preventing and managing the global epidemic, WHO Technical Report Series 894); Mifflin-St Jeor and Harris-Benedict equations for BMR as published in the original peer-reviewed papers; Karvonen heart-rate-reserve formula (Karvonen, Kentala & Mustala, 1957); Jackson-Pollock skinfold body-fat equations.
• Math & conversions: NIST Special Publication 811 (Guide for the Use of the International System of Units) for unit definitions and conversion factors; CODATA-recommended values where physical constants are involved.
• Currency conversion: reference rates from a major public foreign-exchange API, refreshed daily. Rates are indicative and do not include spreads or fees charged by banks and exchanges.

Editorial standards

• Accuracy first. If a formula has known limitations (for example, BMI is a poor estimator of body composition for very muscular individuals), we say so in the calculator's own page — not buried in a footer.
• No sponsored placements. No calculator on CalcBox is paid for, sponsored, or influenced by any third party. Display ads served on the site are clearly delineated and never embedded inside calculator results or article text.
• Plain English. We write at roughly an 8th-grade reading level. Jargon is defined the first time it appears.
• Corrections. If you spot an error, email us. We correct verified mistakes within 48 hours and note material changes at the bottom of the affected page.
• No medical, legal or financial advice. Our calculators are educational reference tools. They do not replace consultation with a qualified professional in your jurisdiction.

How we update content

Calculators are reviewed at least once per year and whenever the underlying standard changes (for example, when the IRS publishes new federal tax brackets or when the WHO issues revised BMI guidance). Blog articles include a publication date in their metadata and are revisited when reader feedback or new sources indicate an update is warranted. We publish three new educational articles per week in our blog.

Privacy & advertising

All calculator computations run in your browser; we do not store the values you enter. We collect anonymous traffic statistics (page views, referrer, country at the country level) to understand which tools are most useful. Third-party advertising partners may set cookies in accordance with their own policies, which you can review and opt out of via the standard ad-personalisation controls. See our privacy policy and terms of use for the full disclosure.

Contact

Found a bug, want a new calculator, have a correction, or want to discuss our methodology? We read every message.

• Email: contato@calcboxapp.com
• Contact form: /contact