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Percentage Calculator with the working shown

Pick the question you are really asking. The tool prints the answer and the arithmetic behind it, so you can check it by hand or show the working.

Short answerLast edited October 31, 2026

The Percentage Calculator solves the three everyday percentage problems: what a percentage of a number is, what percentage one number is of another, and the change between two values. For example, 80 to 100 is a 25% increase.

How it works

1

Enter the numbers

Add the value and the percentage you are working with.

2

Pick the operation

Choose a share, an increase or a decrease.

3

Read the result

The working is shown next to it.

Which question do you have?

Everyday situationMode to chooseExample
A waiter wants 15% of a billWhat is X% of Y15% of 86.40
A test score of 42 of 50X is what percent of Y84%
Rent went from 900 to 1,050Change from X to Y+16.67%
Add tax to a net priceAdd X% to Ynet × 1.20
A sale price with 30% offTake X% off Yprice × 0.70

The four formulas worth knowing

Percent of a number

Multiply by the percentage and divide by one hundred: 15% of 240 is 240 × 15 ÷ 100 = 36. In shops, "20% off" is the same as multiplying by 0.8.

One number as a percent of another

Divide the part by the whole and multiply by 100. 42 of 50 is 42 ÷ 50 × 100 = 84%. The order matters: swapping the two numbers gives a different answer.

Percentage change

Subtract the old value from the new one, divide by the old, multiply by 100. Going from 900 to 1,050 is 150 ÷ 900 = 16.67% up. Going back down the same amount is not a 16.67% drop — it is 14.29%, because the base changed.

Percentage points are not percent

An interest rate rising from 4% to 6% is up 2 percentage points, or 50% relative. Politicians and adverts switch between the two; now you can too.

Adding then subtracting the same percentage does not return to the start. 200 plus 10% is 220; 220 minus 10% is 198. Always apply the last percentage to the larger number.
How do I take a percentage off a price?
Multiply by (100 − discount) ÷ 100. For 30% off, multiply by 0.7.
How do I work out the original price after a discount?
Divide the sale price by the same factor. A 30% discount means dividing by 0.7.
What is the difference between percent and percentage points?
A change from 4% to 6% is 2 percentage points, but 50% relative to the original value.
Can I use decimals?
Yes. Type 12.5 or 0.75 and the answer keeps two decimals.
Why is my percentage change negative?
Because the second number is smaller than the first: the value went down.

Percentages Without the Panic

Almost every percentage question reduces to one multiplication. The confusion comes from not knowing which number is the whole.

Find the base first

Ask "percent of what?". A 20% increase on a salary is large; 20% off a coffee is small. Once the base is clear, the operation is obvious.

The ten percent trick

Ten percent of anything is one decimal place moved. From there, build: 5% is half of 10%, 15% is 10% plus 5%, 30% is three times 10%. A 15% tip on 86 comes out at 8.6 + 4.3, which is 12.90 — no calculator needed in the restaurant.

Compounding surprises

Percentages applied in sequence multiply, they do not add. Two 10% increases are a 21% rise, not 20%. Two 10% discounts are an 19% reduction, not 20% — stores call the difference "extra off" for a reason. The discount calculator shows the cascade step by step.

When the percentage is the whole story

"Rated 90% by customers" means nothing without the number of customers. 9 out of 10 and 900 out of 1,000 read the same and carry very different weight. Percentages hide sample sizes; always ask.

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Quick facts

  1. A change is the difference divided by the starting value: 80 to 100 is a 25% rise, while 100 to 80 is a 20% fall.
  2. Percentages do not cancel out: a 20% rise followed by a 20% fall ends 4% below the start, because 1.2 × 0.8 = 0.96.
  3. The SI defines the kilo as exactly 1000 and the centi as exactly one hundredth, which is why conversions are exact, not approximate.BIPM
  4. Since 2019 the kilogram is defined by a fixed value of the Planck constant, not by a metal cylinder in Paris.BIPM

Questions people ask

How do I calculate a percentage of a number?
Multiply the number by the percentage written as a decimal. For 15% of 240, that is 240 × 0.15 = 36. Pick "percent of" in the calculator, enter the two numbers, and the result appears.
How do I work out percentage increase?
Subtract the old value from the new value, divide by the old value and multiply by 100. From 80 to 100 the difference is 20, and 20 divided by 80 is 0.25, so the increase is 25%.
Why is a 50% drop followed by a 50% rise not back to the start?
Each percentage applies to a different base. After a 50% drop, 100 becomes 50, and a 50% rise on 50 gives 75, not 100. Recovering from a fall needs a larger percentage rise than the fall itself.

What this page is about

  • SI units

    The International System of Units maintained by the BIPM, with the metre, kilogram, second and their prefixes defined exactly.

Official sources cited on this page

  1. The International System of Units (SI Brochure)BIPM

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