Percentage Calculator
Find a percentage of a number, what percentage one number is of another, and percentage change.
Processed on your device — no upload
What is X% of Y?
15% of 240 is 36
X is what percent of Y?
36 out of 240 is 15
Percentage change
Change from 80 to 100 is 25
An increase of 25%.
Remove a percentage from a total
Before the 16% was added it was 100
Subtracting 16% from 116 would give 97.44 — which is the wrong answer, and the most common mistake in tax arithmetic.
How to use it
- Find the calculator that matches your question — there are four.
- Fill in the two numbers.
- The answer updates as you type.
How it works
All four calculators are one line of arithmetic each. They are separated because the hard part of a percentage question is never the sum. It is working out which sum you need.
Percentage change is not symmetric, and this catches people constantly. Going from 80 to 100 is a 25% increase. Going from 100 back to 80 is a 20% decrease. Same two numbers, different percentages, because the base changed. A price that rises 25% and then falls 25% does not return to where it started — it ends 6.25% lower.
The fourth calculator exists because of a specific, expensive mistake. To find the pre-tax figure behind a tax-inclusive total, you divide by 1.16 — you do not subtract 16%. On a total of 116, dividing gives exactly 100. Subtracting 16% gives 97.44, which is wrong by 2.56 and wrong in the direction that under-reports your income.
The tool shows both answers side by side for that reason: the correct one, and the one you would have got by subtracting, so the size of the error is visible rather than theoretical.
A worked example
A restaurant bill comes to 240 and you want to leave a 15% tip.
First calculator: 15% of 240 is 36. The total is 276. Straightforward.
Now the one that costs money. You are self-employed, you invoiced a client for 116 including 16% sales tax, and you need to report the pre-tax amount.
Fourth calculator: enter 116 and 16. The answer is 100 — and beneath it the tool notes that subtracting 16% would have given 97.44. Check it: 16% of 100 is 16, and 100 + 16 = 116. The division is right. The subtraction takes 16% of the larger number, which is not the tax that was added.
Over a year of invoices that error compounds into a real misstatement, and it always runs in the same direction.
The asymmetry example. Third calculator, 80 to 100: a 25% increase. Swap them, 100 to 80: a 20% decrease. Neither is wrong. The percentage is always relative to where you started, and the starting point changed.
The same trap appears in discounts. An item marked down 40% and then a further 20% off is not 60% off. It is 52%, because the second discount applies to the already-reduced price. Chain the third calculator twice to check any offer that stacks.
For discounts on quantities rather than prices, other arithmetic tools are in the same section.
Questions
Can I use this for VAT or a markup?
Yes. Adding VAT is a percentage increase, and removing it is finding the original before an increase, which is the calculation people get wrong. A markup is the same arithmetic applied to a cost price.
How do I find the pre-tax amount from a total?
Divide by 1 plus the rate. For 16% tax on a total of 116, divide by 1.16 to get 100. Do not subtract 16% — that gives 97.44, which is wrong.
Why is subtracting the percentage wrong?
Because the tax was calculated on the smaller pre-tax figure, not on the total. Subtracting takes the percentage of the larger number, which removes too much.
Why is a 25% rise not cancelled by a 25% fall?
Because the second percentage applies to a bigger number. 100 rises to 125, then 25% of 125 is 31.25, leaving 93.75 — not 100.
How do stacked discounts work?
They multiply rather than add. 40% off then 20% off leaves 0.6 × 0.8 = 0.48 of the price, a 52% discount rather than 60%.
How do I calculate a tip?
Use the first calculator: the tip percentage of the bill. 15% of 240 is 36.
Is anything uploaded?
No. All four calculators run in your browser, so invoice figures and salaries stay on your device.
What is the difference between percentage points and percent?
A rate moving from 4% to 6% has risen two percentage points, but 50 percent. Both are correct and they describe different things — news reports frequently confuse them.
Can I calculate a percentage decrease?
Yes — the third calculator handles both directions. A negative result is a decrease, and the size is shown in words below it.
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