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TinySolve

Percentage Calculator

Work out percentages four ways — of a number, as a proportion, as a change, or added on.

Runs in your browser — nothing you type is sent anywhere

What is X% of Y?

%

Enter both numbers

The answer appears here as you type — there is no button to press.

About the Percentage Calculator

Almost every percentage question people actually have is one of four, and they are easy to confuse with each other. Finding 20% of 850 is a different operation from working out what percentage 170 is of 850, and both differ from the rise between two figures. This calculator keeps them as separate tabs so you pick the question first and cannot accidentally answer a different one.

The one that trips people most often is percentage change, because it is not symmetric. A price that rises from 100 to 150 has gone up by 50%, but falling from 150 back to 100 is a drop of only 33.3%. The starting figure is the base, so swapping the two numbers does not simply flip the sign. This is why a shop can advertise a 50% increase and a 33% sale and end up exactly where it began.

Percentage change from zero has no answer at all, and nor does asking what percentage something is of zero. Rather than showing an infinity symbol or a NaN, the calculator says plainly that the question has no answer and why. Results are also trimmed to four decimal places, so a third of something reads as 33.3333% instead of a long string of floating point noise.

Everything updates as you type, with no calculate button, and nothing you enter is sent anywhere.

How to use the Percentage Calculator

  1. Pick the kind of question

    Choose one of the four tabs: a percentage of a number, one number as a percentage of another, the change between two numbers, or adding a percentage on.

  2. Type the two numbers

    Enter both values. Commas as thousands separators are fine, and so are negative numbers and decimals.

  3. Read the answer and the sentence

    The result appears immediately, with a plain-English sentence underneath showing exactly what was calculated so you can check it is the question you meant.

  4. Copy it if you need it

    The copy button puts the result on your clipboard, ready to paste into a spreadsheet, an invoice or a message.

Frequently asked questions

How do I calculate a percentage of a number?
Divide the percentage by 100 and multiply by the number. For 20% of 850: 20 ÷ 100 = 0.2, and 0.2 × 850 = 170. The first tab does this for you, and the sentence underneath shows the figures so you can check them.
What is the formula for percentage increase?
Subtract the original from the new value, divide by the original, and multiply by 100. From 200 to 260 that is (260 − 200) ÷ 200 × 100 = 30%. A negative answer means it decreased rather than increased.
Why isn't a 50% rise cancelled out by a 50% fall?
Because each percentage is taken from a different starting point. 100 rising by 50% gives 150, but 50% of 150 is 75, so falling by 50% lands on 75, not 100. To reverse a 50% rise you need a 33.3% fall.
Why does it say the calculation has no answer?
Two questions genuinely have no answer: what percentage a number is of zero, and the percentage change starting from zero. Both involve dividing by zero, so the result would be infinite rather than a number. Showing that plainly is more useful than printing an error value.
How do I work out a discount percentage?
Use the percentage change tab with the original price as From and the sale price as To. The negative result is the discount. For a price cut from 80 to 60 the answer is −25%, so it is a 25% discount.
Can I use negative numbers?
Yes, and percentage change handles them sensibly. Going from −100 to −50 is reported as a 50% improvement rather than a 50% fall, because the calculation divides by the size of the starting figure rather than its signed value.

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