Percentage Calculator

The traps worth knowing

• Increases and decreases do not cancel. Add 20 percent then take 20 percent off and you land at 96 percent of where you started, not 100.
• Percentage points are not percent. Moving from 5 percent to 7 percent is a rise of two percentage points and of forty percent. Both are true and they mean different things.
• Discounts do not add. Thirty percent off then a further twenty percent off is 44 percent off in total, not fifty.
• Reversing a percentage needs division. If a price including 20 percent tax is 120, the price before tax is 120 divided by 1.2, not 120 minus 20 percent.
• Averaging percentages is usually wrong unless the groups behind them are the same size.

Worked examples

The five calculations the tool offers, each shown with real numbers so you can check you have picked the right one.

Notice that the first two are the same relationship read from different ends, which is why the wording of a question matters so much. What is 15 percent of 80 and 12 is what percent of 80 describe one fact and ask for different parts of it.

Percentages in everyday money

Three cases account for most of the percentage arithmetic people actually do, and each has a trap in it.

A sale price. Thirty percent off then a further twenty percent off is not fifty percent off. The second discount applies to the already reduced price, so you pay 0.7 times 0.8, which is 56 percent of the original: a 44 percent discount. Retailers know this and word the signs carefully.

Tax on a price. Removing tax from a total means dividing, not subtracting. A price of 120 including 20 percent tax was 100 before tax, because 100 times 1.2 is 120. Subtracting 20 percent from 120 gives 96, which is wrong by four.

A tip or service charge. Adding 10 percent and then paying tax on the total is a different amount from paying tax and then adding the tip. Which order applies depends on the jurisdiction and is worth checking on a large bill.

Percentage points, and why the distinction matters

This is the one that gets misreported constantly. If an interest rate moves from 5 percent to 7 percent, that is a rise of two percentage points. It is also a rise of forty percent, because two is forty percent of five. Both statements are true and they sound wildly different.

Headlines pick whichever is more dramatic, which is why the same change can be reported as a modest two point rise or an alarming forty percent jump. Neither is a lie, and knowing which one is being used tells you a great deal about who is writing.

The rule is simple: percentage points describe the arithmetic gap between two percentages, and percent describes the relative change. When a figure is itself a percentage, say which of the two you mean, because the reader cannot tell otherwise.

The same care applies to anything reported as a change in a rate: unemployment, market share, conversion rate, interest. A change from 1 percent to 2 percent is one percentage point and a doubling, and describing it either way without saying which is how statistics get misused.

Free, with no account

There is no limit on how many conversions you make, no sign up wall and no paid tier. The percentage calculator costs nothing to run because the arithmetic happens on your device, so there is nothing to meter.

The page is also small. One stylesheet and one script, together less than a single photograph, which means it loads in well under a second on a phone connection rather than after several seconds of adverts and trackers.

Every other tool on the site works the same way. Over a hundred of them, all running in the browser, none of them asking for an account and none of them uploading anything you give them.

How to use it

Type into the field and the answer appears as you go. There is no calculate button to press and no page reload, because the arithmetic is a few milliseconds of work happening on your own device rather than a round trip to a server.

Every control recalculates immediately when you change it, so you can try several variations without retyping the numbers. The result stays selectable, so you can copy it straight into whatever you were filling in.

On a phone the layout stacks and the number fields open a numeric keypad rather than the full keyboard. Nothing about the tool is held back for a desktop, and nothing is hidden behind a menu.

What it will not do

This is a calculator, not advice. It tells you what a number is, not what you should do about it, and it has no way of knowing the fees, taxes or terms attached to whatever transaction you are planning.

Nothing is saved between visits. Close the tab and the figures are gone, which is the correct behaviour for a tool you reached for once to check one thing, and the reason there is no history to opt out of.