Percentage Calculator

Solve the three everyday percentage problems: a percent of a number, one number as a percent of another, and percent change.

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How to use the percentage calculator

Pick the type of question you want to answer, then fill in the two values. The answer appears straight away along with the arithmetic used, so you can check the logic or copy it into homework. Switch between modes at any time – your numbers stay in place.

The three percentage formulas

1. What is A% of B? Multiply B by A and divide by 100. For example, 15% of 200 is 200 × 15 ÷ 100 = 30. This is the calculation behind discounts, tips and sales tax.

Result = A ÷ 100 × B

2. A is what percent of B? Divide A by B and multiply by 100. If you answered 42 questions out of 50 correctly, your score is 42 ÷ 50 × 100 = 84%.

Percent = A ÷ B × 100

3. Percent change from A to B. Subtract the old value from the new one, divide by the old value and multiply by 100. A price that rises from $80 to $100 has increased by 25%. A fall from $100 to $80 is a 20% decrease – the base is different, so the percentages are not symmetric.

Change = (B − A) ÷ |A| × 100

In change mode the calculator also shows the "percentage difference", which compares two values relative to their average. It is useful when neither value is the obvious starting point.

Common percentage mistakes

  • Adding percentages in sequence: a 50% rise followed by a 50% fall leaves you 25% below where you started, not back at zero.
  • Percent versus percentage points: an interest rate moving from 4% to 5% is a rise of one percentage point but a 25% increase.
  • Wrong base: always divide by the original value when measuring change.

Need to work with fractions instead? Try the fraction calculator.

Frequently asked questions

How do I calculate a percentage of a number?

Multiply the number by the percentage and divide by 100. For example, 20% of 150 is 150 × 20 ÷ 100 = 30.

How do I calculate percentage increase?

Subtract the original value from the new value, divide by the original value and multiply by 100.

What is the difference between percent change and percentage difference?

Percent change uses the starting value as the base. Percentage difference uses the average of both values, so it is the same in either direction.

Why isn’t a 10% increase then a 10% decrease zero?

Because the decrease is applied to a larger number. 100 → 110 → 99, an overall 1% decrease.

Last reviewed 2026-10-27. This percentage calculator is provided for general information; verify important decisions with a qualified professional.