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About

Percentage Calculator

Five sentences, each with three boxes: fill in any two and the one left over is worked out exactly, with the arithmetic shown. The usual percentage page has a separate form for each direction; here, typing 240 and −20% into “from 300 to 240 is a change of −20%” turns the first box into the price before the discount.

What it does

  • Percent of, percentage change, percentage difference, percentage points and percent error, each a sentence with three boxes.
  • Any box can be the one worked out, so the figure before a rise, a discount or a tax has a place.
  • Exact arithmetic: 5% of 17.99 is 0.8995, and a result that repeats, like a third, says so instead of being rounded.
  • The working with the numbers filled in, so every answer can be checked.
  • Pasted numbers read either way, 1,234.56 or 1.234,56, and a percent sign allowed in the boxes.
  • A question with no answer answered in words, such as “nothing is a percentage of 0”.
  • The percentage also read as a decimal and as a fraction; the answer copied in a click.

How to use it

  1. Pick the sentence that matches the question.
  2. Fill in the two boxes you know.
  3. Read the answer and the working under it.
  4. Copy it.

What it does not do

  • Tip, discount, VAT, margin and markup as separate forms: each is the change sentence under another name, and five more tabs would bury the five that differ.
  • A history of past sums: each answer is a sentence to copy, working and all.

Questions

Percentage change or percentage difference?

Change has a reference: from the old value to the new. Difference has none: two values measured against their average, for when neither comes first.

Percentage points or percent?

A rate that goes from 10% to 12% is up 2 percentage points and up 20 percent. Both are true, and people argue about which was meant, so both are shown.

Why does another calculator give 0.8994999?

It works in binary floating point, where 17.99 cannot be stored exactly. This one works on whole numbers with a scale, so decimals come out exact.

How do I find the price before a discount?

In the change sentence, leave the first box empty, put the final price in the second and −20% in the third: 240 after a 20% discount was 300. Adding 20% back to 240 gives 288, which the working warns against.

Everything here runs in your browser. Nothing you type, paste or open is uploaded, and there is no account and no queue. How that works.

For one job

Often used with

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