About Stepwise

Most calculator sites hand you a number and leave. You get a monthly payment with no indication of what it includes, a BMI with no explanation of what it fails to measure, and a body of text below the tool that was written for a search engine rather than for you.

That is a problem when the number matters. A mortgage figure that quietly omits property tax and insurance is not a small inaccuracy — it can understate the real monthly cost by a quarter. A freelance rate calculator that divides target income by 2,080 hours produces a number that would bankrupt you.

So every calculator here states the formula it uses, defines each variable, works through a real example, lists what it assumes, and says where its answer stops being reliable. You should be able to reproduce the result on paper if you want to.

There are currently 278 calculators across 13 categories. Each one is a single definition containing its input schema, its calculation, its explanation and its tests, so the maths and the documentation cannot drift apart.

Every calculator must pass an automated suite before it can ship. That suite checks that it:

• produces a valid result from its own default values;
• never renders NaN, Infinity or undefined;
• fails with a specific, actionable message rather than crashing on bad input;
• carries a formula, a worked example that actually runs, assumptions and limitations;
• links only to calculators that exist, and never to itself;
• has a unique title and meta description of a usable length.

The financial mathematics is verified against independently computed values — annuity payments, amortisation schedules that close to exactly zero, effective annual rates, IRR checked by confirming that net present value at that rate is zero. The hash functions are checked against their published test vectors.

Formulas are standard and cited where a source adds value: the Mifflin–St Jeor equation for metabolic rate, the US Navy circumference method for body composition, the WHO BMI categories, the exact 1959 definitions of the inch and the pound.

Where a figure is a convention rather than a constant — the 7,700 calories per kilogram used in weight planning, the 238 words per minute reading speed — the calculator says so rather than presenting it as settled fact.

Every calculator shows the date its formula and content were last reviewed. See how we calculate for the full methodology.

Calculations run in your browser. Your salary, your loan balance, your date of birth and your body measurements are never transmitted to a server, because there is no server call to make.

This is not a policy we could quietly reverse — it is how the software is built. You can confirm it in thirty seconds with your browser’s network inspector. The privacy policy describes the few things that are recorded, which is essentially just standard web server logs.

• Put an advert between you and your result, or style one to look like a button.
• Require an account to use a calculator.
• Claim to be “the most accurate calculator on the internet”. We show the formula instead.
• Publish thin pages generated to capture a keyword.
• Invent FAQs, testimonials, authors or review counts.
• Present an estimate as professional financial, medical or legal advice.

If a calculator gives a wrong answer, we want to know — and we would rather hear about it from you than not hear about it at all. Every calculator page has a report an error link. Tell us what you entered and what you expected, and we will check the formula against its source.