About this site

What this is

Percentage Calculator is a free set of tools for the calculations percentages are usually needed for: a percentage of a number, what share one number is of another, percentage increase and decrease, change, difference, and discounts. Every tool shows the formula and the steps alongside the answer.

How it works

The site is a static website. Every calculation runs in your browser using JavaScript that ships with the page — there is no calculation server, no API call, and nothing to wait for. The practical consequences:

• Results appear instantly, with no network round trip.
• The numbers you type never leave your device.
• Once a page has loaded, the calculators keep working even if your connection drops.

How the calculators are built

All the arithmetic lives in one shared module with an automated test suite covering the worked examples, decimals, negative values, very large numbers, division by zero, floating-point precision and rounding. The step-by-step explanations are generated by that same tested module rather than written separately, so the working shown always matches the answer given.

Three principles shape the rest:

• Show the working. An answer you cannot check is not much use. Every result includes the formula, your numbers substituted into it, and each step in plain language.
• Be honest about precision. Repeating decimals are marked with ≈ rather than presented as exact.
• Explain the distinctions. Percentage change, difference, increase and decrease are routinely treated as interchangeable. They are not, and the site says so wherever the confusion is likely.

What it is not

These are general-purpose tools for everyday arithmetic. They are not financial, tax, medical or legal advice, and results should be checked independently before being relied on for anything consequential. See the disclaimer for the full position.

Corrections and suggestions

If you find a result that looks wrong, an explanation that is unclear, or a calculator that is missing, please get in touch. Reports of incorrect results are taken seriously — accuracy is the only thing that matters here.