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Percentage Calculator

Three percentage problems, one tool. Find X% of a number, work out what percent one number is of another, or measure the percentage change between two values.

Result

30

X

15

Y

200

Tip: for percentage change, a negative result means a decrease and a positive result means an increase.

How it works

A percentage is just a fraction of 100. 'Percent' literally means 'per hundred', so 25% is 25/100, or 0.25. Every percentage problem reduces to multiplying or dividing by that decimal.

'What is 15% of 200?' converts 15% to 0.15 and multiplies: 0.15 × 200 = 30. 'X is what % of Y?' divides X by Y and multiplies by 100. Percentage change compares the difference to the starting value — which is why going from 100 to 150 is +50%, but going from 150 back to 100 is only −33%.

That asymmetry trips people up constantly: a 50% loss needs a 100% gain to break even. The direction of change matters because the base you divide by changes.

X% of Y          = (X / 100) × Y
X as % of Y      = (X / Y) × 100
% change X → Y   = ((Y − X) / |X|) × 100

Frequently asked questions

How do I calculate a percentage of a number?

Convert the percentage to a decimal by dividing by 100, then multiply. For 15% of 200: 15 ÷ 100 = 0.15, and 0.15 × 200 = 30.

How do I work out what percent X is of Y?

Divide X by Y and multiply by 100. For example, 45 out of 60 is (45 ÷ 60) × 100 = 75%.

How is percentage change calculated?

Subtract the old value from the new value, divide by the old value, then multiply by 100. Going from 80 to 100 is ((100 − 80) ÷ 80) × 100 = +25%. A negative result means a decrease.

What's the difference between percentage points and percent?

If an interest rate goes from 4% to 6%, it rose 2 percentage points — but that's a 50% relative increase. Percentage points measure absolute differences between percentages; percent measures relative change.

Why doesn't a 50% decrease then a 50% increase get back to the start?

Because each change is measured against a different base. 100 minus 50% is 50; adding 50% of 50 only gets you to 75. To undo a 50% drop you need a 100% gain.