How We Calculate

Calculators Cafe is an independent project. Our aim is simple: give you the same number a careful analyst would reach by hand, and show you exactly how it was reached. Nothing is hidden behind a black box — if you disagree with a result you can follow the formula and check it yourself.

1. Standard, published formulas

We use the formulas that banks, tax authorities and medical bodies publish, and we say which one we used. Examples:

Loans: the reducing-balance EMI formula.
Income tax: the slab rates, rebate and cess notified for the financial year shown on the page.
BMI and BMR: the standard BMI index and the Mifflin-St Jeor equation.
Unit conversion: fixed, internationally defined conversion factors (for example, 1 inch = 2.54 cm exactly).

2. Rates are configurable, and dated

Rates that change over time — income tax slabs, EPF and PPF interest, GST rates, capital gains rates — are stored in one configuration file rather than buried in code. Each affected page states the year it applies to. When a rate changes, we update it in one place and every related calculator follows.

3. Worked examples on every page

Each calculator includes a worked example with real numbers, so you can sanity-check the result before trusting it. If our example and the calculator disagree, that is a bug and we want to know about it.

4. How we verify

Every formula is tested against hand calculations and, where possible, against an official calculator.
The automated test suite covers the calculators and the site itself, so a change cannot silently break an existing tool.
Currency, regional rules and rounding behaviour are stated on the page where they matter.

5. What our results are not

Our calculators are for general information and planning. They are not financial, investment, tax, legal or medical advice. Real outcomes depend on lender terms, fees, market movements, your personal circumstances and rules we cannot see. Always confirm important figures with a qualified professional or the official authority before acting.

6. Corrections and feedback

Spotted a mistake? Please tell us. Send the calculator name, the inputs you used and the result you expected, and we will investigate and correct it. Accuracy is the whole point of this site, so reports are genuinely welcome.