About Countora
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Countora is an independent website of free online calculators. It covers four areas: construction and DIY projects, math, health, and personal finance. Every calculator is free to use, and you don't need an account.
Why we built it
Many calculators online give you a number with no explanation. You can't see how it was worked out or which assumptions went into it. We think you should be able to check the answer. So every calculator page onCountora shows:
- the formula, written out in plain language
- a worked example with real numbers that you can check by hand
- tips and common mistakes, plus answers to frequent questions
- the sources behind any figures it relies on, and the date the page was last reviewed
How the calculators are built
The math behind each calculator is kept separate from the page design and covered by automated tests, so normal inputs, edge cases and unit conversions are checked every time the site is updated. Health and finance pages cite government agencies, regulators, professional bodies or published research, not other calculator sites. Our methodology page explains our rounding rules, waste allowances and other assumptions in detail.
What the calculators are not
The results are estimates for general information. They aren't professional, medical, financial, tax or legal advice. Read our disclaimer for more.
How the site is funded
Countora may show advertising and may earn a commission from some product links. Neither ever changes what a calculator tells you. Our affiliate disclosure explains how this works.
Get in touch
Found a mistake, or want a calculator we don't have yet? Contact us. We read every message, and corrections to formulas or figures come first.