CalcArcade.

Percentage Calculator

Three common percentage problems in one place. Fill in any pair of boxes and the answer appears instantly.

Your numbers

A. X% of Y
B. X is what % of Y
C. Percent change
Result

How we calculate it

X% of Y = X ÷ 100 × Y. X is what percent of Y = X ÷ Y × 100. Percent change = (new − old) ÷ |old| × 100.

For example, 15% of 240 is 36, 45 is 25% of 180, and going from 80 to 100 is a 25% increase.

How to read your result

  • "X% of Y" gives the part: for example 15% of 200 is 30.
  • "X is what % of Y" gives the share: for example 30 is 15% of 200.
  • "Change from X to Y" gives the percent increase or decrease, with the starting value as the base.
  • Each result is a separate question: fill in only the boxes for the one you need.

Common mistakes

  • Using the wrong base. Percent change always divides by the starting value, not the ending one.
  • Adding and subtracting percents. A 20% rise followed by a 20% fall does not bring you back to the start.
  • Mixing up percentage points and percent. Going from 4% to 5% is one percentage point and a 25% increase.
  • Typing 0.15 when the box expects 15. Enter the percent as a plain number.

Assumptions and limits

  • A percent change is not symmetric: a 50% increase followed by a 50% decrease does not return you to the starting value.
  • Percent change from zero is undefined, so the calculator skips it.

Frequently asked questions

How do I calculate a percentage of a number?

Divide the percentage by 100 and multiply by the number. 20% of 150 is 0.2 × 150 = 30.

How do I find what percent one number is of another?

Divide the part by the whole and multiply by 100. 45 out of 180 is 45 ÷ 180 × 100 = 25%.

What is the difference between percent and percentage points?

Going from 10% to 12% is a 2 percentage point rise but a 20% relative increase.

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Worked example (a fixed example using the starting numbers, it does not change as you type)

Inputs: What is (percent) % … = 15; … of (number)? = 240; (number) … = 45; … is what % of (number)? = 180; Change from (old value) … = 80; … to (new value) = 100.

  • 15% of 240 36
  • 45 is what % of 180 25%
  • Change from 80 to 100 25%

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Last reviewed: . Formulas and assumptions are described on our methodology page. For information only; not professional advice.