Toolkeel

Percentage calculator

Three everyday percentage questions, answered as you type: how much is X% of Y, what percent is A of B, and how much did something go up or down.

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What is X% of Y?

Result

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X is what percent of Y?

Result

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Percentage change from X to Y

Change

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How to use it

  1. Choose the question that matches yours.

  2. Type the two numbers.

  3. Read the answer; it updates as you type.

About this tool

The formulas: X% of Y = X ÷ 100 × Y. A as a percent of B = A ÷ B × 100. Percentage change = (new − old) ÷ |old| × 100. A positive result is an increase, a negative one a decrease.

A common trap: a 50% increase followed by a 50% decrease does not return to the start (100 → 150 → 75), because the second percentage applies to a bigger number.

Good to know

  • "Percentage change" is undefined when the old value is 0.
  • Results are rounded to two decimal places.

Frequently asked questions

How do I calculate 20% of a number?

Multiply the number by 0.20. For example, 20% of 250 is 50. Type 20 and 250 in the first calculator.

How do I calculate percentage increase?

Subtract the old value from the new value, divide by the old value and multiply by 100. From 80 to 100 is a 25% increase.

What is the difference between percent and percentage points?

If an interest rate rises from 4% to 5%, it rose by 1 percentage point, which is a 25% increase in the rate itself.

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Last updated 2026-10-20 by the Toolkeel team. How we build and check our tools.