About Calcboxer

Calcboxer is a collection of 600+ free online calculators — from BMI and percentages, through loan instalments and car TCO, to tools for AI Act and GDPR compliance. Everything runs in your browser, no signup and no fees, in English and Polish.

Why this site exists

Calcboxer grew out of a simple frustration. The web has plenty of calculators, but most have at least one of three problems: (1) they force a single unit system — metric-only or US-only, never both; (2) they don't show the formula, so you can't see what's happening under the hood; (3) they're wrapped in popups, signup walls and "premium" tiers.

Calcboxer does things differently:

You choose units and currency — switch between metric (kg, km, L) and US customary (lb, mi, gal) in the page header, and pick USD, EUR, PLN or GBP. Every calculator respects your choice, including the formula explanation.
Every result shows the formula — the "How results are calculated" section reveals the exact formula and steps. If you want to verify by hand, you can.
Fully available in English and Polish — not only the interface, but also formula explanations, FAQs and examples are localised.

How we verify formulas and choose sources

For each calculator we rely on primary sources or widely accepted formulas:

Health — BMI classification per the World Health Organization, the Mifflin-St Jeor (1990) equation for BMR/RMR, Katch-McArdle when body-fat % is known, Devine and Lorentz formulas for ideal body weight, Mosteller formula for BSA.
Finance — standard annuity loan payment formula, APR per the EU Consumer Credit Directive 2008/48/EC, compound interest, VAT per each country's VAT law.
Physics & math — textbook formulas drawn from university materials (Halliday/Resnick, Griffiths) and standard high-school references.
Motoring and ecology — CO₂ emissions following the UK DEFRA methodology and the EPA GHG Emission Factors Hub, L/100 km ↔ mpg conversions from SI definitions.
Construction — typical material coefficients published by manufacturers and European norms (PN-EN) for concrete, adhesives, mortars and paints.
AI regulation / GDPR — Article 83 GDPR for fine estimates, EDPB guidelines for DPIA, the EU AI Act (Regulation 2024/1689) for AI system risk classification.

Each calculator page includes the sections: What this calculator computes, Formula, Variables (definitions), Step by step, Interpretation of the result and Units. For educational categories (physics, math) you'll also find historical notes and links to Wikipedia and primary sources.

Limitations we state openly

A calculator is an indicative tool — it does not replace a specialist:

Health calculators (BMI, BMR, TDEE, child percentiles) are estimates. BMI doesn't distinguish muscle from fat; for athletes and pregnant users results may be misleading. When in doubt — consult a doctor or dietitian.
Finance calculators do not account for all bank fees, tax reliefs or future rate changes. For loan, deposit or investment decisions, consult a financial adviser or accountant.
Tax calculators (VAT, income tax, inheritance) are simplifications — real tax treatment depends on the specific situation, the tax authority's interpretation and the current legal status.
Regulation calculators (GDPR, AI Act) are educational. Actual obligations and sanctions are determined by the supervisory authority.

Privacy and trust

Calculations run locally in your browser — the values you enter (weight, income, medical data, costs) are not sent to our servers. Exception: some ecology calculators use coefficients fetched from our server, but your own inputs are still not transmitted.
No signup — using a calculator requires no account or personal data.
Advertising (Google AdSense) covers hosting and development costs. You can opt out of personalized ads following the instructions in our Privacy policy.
Traffic analytics (Google Analytics) — aggregated data about visits, without identification of individuals.

Updates and ongoing development

Content is reviewed and expanded regularly. When a regulation changes (VAT rate, minimum wage, VAT exemption threshold, income tax brackets), the affected calculators are updated. Bug reports and suggestions are treated as a priority.

Last major update: April 2026.

Contact and feedback

Questions, suggestions for new calculators, or bug reports (e.g. unexpected result, typo, outdated coefficient) — write to contact@calcboxer.com. We typically reply within 1–3 business days. For advertising partnerships — see the Partnership page.