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Percentage Calculator

Pick one of four questions — what is X% of Y, X is what percent of Y, the percentage change between two numbers, or adding and removing a percentage — and type your numbers. The answer updates as you type and shows the working. For example, 15% of 240 is 0.15 × 240 = 36.

Runs entirely in your browser

Updated

How to use the Percentage Calculator

  1. 1Pick the type of question you want to answer using the tabs.
  2. 2Type your numbers — the result updates as you type.
  3. 3Read the worked explanation below the answer to check the method.
  4. 4Switch tabs at any time; each keeps its own values.

How it works

A percentage is just a fraction with 100 on the bottom. Every calculation here is that one idea rearranged: to find a part you multiply, to find a rate you divide, and to find a change you compare the difference with where you started.

The one people most often get wrong is percentage change, because it matters which number you divide by. Going from 50 to 75 is a 50% increase, but going back from 75 to 50 is a 33.3% decrease — the same gap measured against a different starting point.

Results are rounded for display but calculated at full precision, so chaining answers together does not accumulate rounding error.

The formula

part = (percent ÷ 100) × whole percent = (part ÷ whole) × 100 change = ((new − old) ÷ old) × 100
percent
the rate, written without the % sign
whole
the number the percentage is taken from
part
the resulting amount
old / new
the values before and after the change

Percentage change always divides by the original value, which is why an increase and the decrease that undoes it are different percentages.

Worked example

A £80 jacket is reduced to £60

  1. Choose the percentage change tab.
  2. Enter 80 as the original value and 60 as the new value.
  3. The tool computes (60 − 80) ÷ 80 × 100.

Result: A 25% decrease — a saving of £20.

Tips and common mistakes

  • For a percentage change, always divide by the starting value. Going from 50 to 75 is a 50% rise; going back from 75 to 50 is a 33.3% fall.
  • Percentages can be swapped: 8% of 50 is the same as 50% of 8, which is 4. Pick whichever is easier to work out in your head.
  • Say “percentage points” when comparing two rates. A rate that moves from 4% to 6% has risen by 2 points, or by 50%.
  • Check that the answer is sensible: a part should be smaller than the whole unless the percentage is over 100.

Frequently asked questions

How do I work out a percentage of a number?
Divide the percentage by 100 and multiply by the number. 15% of 240 is 0.15 × 240 = 36.
Why is a 50% rise not cancelled by a 50% fall?
Because each is measured against a different base. 100 rising by 50% gives 150; 150 falling by 50% gives 75, not 100. To undo a 50% rise you need a 33.3% fall.
What is the difference between percent and percentage points?
If a rate moves from 4% to 6% it has risen by 2 percentage points, but by 50 percent. Percentage points measure the gap between two rates; percent measures relative change.
How do I add tax or a tip to a price?
Use the "Add or subtract a percentage" tab. It multiplies by 1 plus the rate, so 20% added to 50 gives 60.
How do I find what percentage one number is of another?
Divide the part by the whole and multiply by 100. 18 out of 24 is 18 ÷ 24 × 100 = 75%.
How do I undo a percentage increase?
Divide by one plus the rate rather than subtracting the percentage. A price of 120 after a 20% rise was 120 ÷ 1.2 = 100, not 96.
How do I calculate a percentage decrease?
Subtract the new value from the old, divide by the old value and multiply by 100. From 80 to 60 is (80 − 60) ÷ 80 × 100 = 25%.
Can I average percentages?
Only when each one is out of the same total. Otherwise add up the underlying amounts and totals and divide once: 9 out of 10 and 60 out of 100 is 69 out of 110, which is 62.7%, not the 75% a simple average gives.
Why don't my percentages add up to exactly 100%?
Usually because each figure was rounded separately: three equal shares of 33.3% round to 33% each, totalling 99%. Show one decimal place, add a note about rounding, or give the missing point to the figure with the largest remainder.
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