Percentage Calculator

A percentage calculator that covers all six questions people actually mean by “percentage” — and shows the formula and substituted numbers behind every answer, so you can check it rather than trust it.

How to use Percentage Calculator

  1. Pick the mode that matches your question — “% of”, “X is what % of Y”, increase or decrease, add or subtract a %, reverse a %, or percentage difference.
  2. Type your two numbers. The answer updates as you type; there is no submit button.
  3. Read the working panel under the result to see the exact formula and the values substituted into it.
  4. Use the tip, discount and VAT helper at the bottom for the three most common real-world percentage jobs.
  5. Copy the answer, or copy the full working line, with one click.

About Percentage Calculator

The word “percentage” hides at least six different sums, and most calculators only do one or two. Working out 15% of 240 is a different operation from working out that 36 is 15% of 240, which is different again from knowing that a price rose from 240 to 276 — a 15% increase. Add reverse percentages (what was the price before VAT?), percentage difference (a symmetric comparison of two measurements) and add-or-subtract-a-percent, and you have the full set. This tool puts all six in one page so you never have to work out which calculator you need.

Every mode prints its working. The result panel shows the general formula, then the same formula with your numbers substituted, then the answer — the way a maths teacher would set it out. That matters more than it sounds: percentage mistakes are almost never arithmetic mistakes, they are base mistakes, where the wrong number ends up as the denominator. Seeing (276 − 240) ÷ 240 × 100 written out makes an incorrect base obvious in a way that a bare “15%” never can.

The tip, discount and VAT helper handles the everyday jobs on their own terms: a bill split between diners with the service charge included, a sale price with the saving shown in cash as well as percent, and VAT added or removed at any rate — 20% and 5% for the UK, or whatever rate your country uses. Reverse VAT in particular trips people up constantly, because subtracting 20% from a VAT-inclusive total does not give the net figure. The tool always divides rather than subtracts, and shows that it did.

Frequently asked questions

How do I calculate a percentage of a number?

Divide the percentage by 100 and multiply by the number. For example 15% of 240 is 0.15 × 240 = 36. The “% of” mode does this and prints the substituted formula alongside the answer.

What is the difference between percentage change and percentage difference?

Percentage change has a direction: it measures how far the new value moved from the old one, so the old value is the denominator. Percentage difference is symmetric — it compares two values against their average and gives the same figure whichever order you enter them.

How do I work out the original price before VAT or a discount?

Divide the final amount by 1 plus the rate as a decimal. £120 including 20% VAT was £120 ÷ 1.20 = £100 before VAT. Subtracting the percentage from the final price is the classic mistake and gives £96, which is wrong.

Why does a 50% rise followed by a 50% fall not return to the start?

Because the two percentages are taken from different bases. 100 rises by 50% to 150, then falls by 50% of 150, which is 75. Percentages compound multiplicatively: 1.5 × 0.5 = 0.75, a net 25% loss.

Is this percentage calculator free and private?

Yes. It is free with no sign-up, and every calculation runs in your browser — no number you type is ever sent anywhere.

Can it handle negative numbers and decimals?

Yes. Decimals are accepted everywhere, and negative values work in all modes. Percentage change from a negative starting value is flagged, because the sign convention there is genuinely ambiguous.

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