Percentage Calculator

How to use the Percentage Calculator

1. Pick a mode: % of a number, What %, Increase, Decrease or % change.
2. Fill both fields. Labels change with the mode: percentage and number, part and whole, original and percent, or from and to.
3. The result updates as you type. Use Calculate if you want to force a check, Swap values to flip the two boxes, Copy result for the figure alone, or Clear to empty the fields.
4. Read the worked line under the answer so you can see what was calculated.

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What it is for

% of a number answers “what is 15% of 200?”. What % answers “30 is what percent of 200?”. Increase and Decrease take an original amount and a percent and return the new amount, plus the difference. % change is the move from one figure to another, such as a price that went from 80 to 100, or a score that dropped.

Use it for VAT-style add-ons, discounts, test scores, tips and simple growth. It is not a tax engine and it will not apply a rate to a basket of goods. For adding or removing VAT at a set rate, use the VAT Calculator.

Why it runs in your browser

The arithmetic stays in the tab. You do not upload a spreadsheet and Catpool does not keep the numbers. Close the page and the fields are empty.

Two percentage traps

Percent versus percentage points

If a savings rate rises from 4% to 5%, it has gone up by one percentage point, but by 25% in percent terms. Put 4 and 5 into % change and you will see 25%. News stories and adverts sometimes mix the two, so it is worth checking which one is meant.

Finding the price before a discount

A jacket costs £40 in a 20% off sale. The original price was not £48. The sale price is 80% of the original, so divide £40 by 0.8 to get £50. You can check it with Decrease: £50 decreased by 20% gives £40.

The same idea works for VAT. A £120 price that includes 20% VAT is £100 before VAT, not £96, because £120 is 120% of the net price.

Common questions

Is “15% of 200” the same as “200 is what percent of 15”?

No. Those are the first two modes, and they are not interchangeable. If the answer looks like nonsense, you are probably in the wrong tab, or you can hit Swap and see if the labels now match the question.

Why can I not work out a percentage of zero?

Dividing by zero is undefined. “What %” needs a whole that is not zero. “% change” needs a “from” value that is not zero.

How many decimal places do you show?

Up to four if they are needed, fewer if the result is a whole number. Copy takes that same figure.

Does Increase add the percent on top of the original?

Yes. 80 increased by 25% is 100. Decrease works the other way: 80 decreased by 25% is 60. The line under the result states the difference as well.

Is % change the same as Increase?

No. Increase starts from an amount and a percent. % change starts from two amounts and tells you the percent that sits between them.

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