How to use the percentage calculator
- 1Pick the type of calculation, such as "What is X% of Y?" or "Percentage change".
- 2Enter your two numbers. The answer updates as you type.
- 3Check the formula shown under the result to see how it was worked out.
- 4Press Copy to copy the answer.
The formulas
All percentage questions come down to one relationship: part = percent × whole ÷ 100. The calculator rearranges it for each question.
- What is X% of Y? Multiply Y by X and divide by 100. For example, 15% of 80 is 80 × 15 ÷ 100 = 12.
- X is what percent of Y? Divide X by Y and multiply by 100. For example, 12 out of 80 is 12 ÷ 80 × 100 = 15%.
- Percentage change from X to Y: subtract the old value from the new value, divide by the old value and multiply by 100. A rise from 80 to 92 is (92 − 80) ÷ 80 × 100 = 15%.
- Increase or decrease by a percentage: multiply by (1 + X ÷ 100) to increase or (1 − X ÷ 100) to decrease. A 20% discount on 50 is 50 × 0.8 = 40.
- X is Y% of what? Divide X by Y and multiply by 100. If 12 is 15% of a number, the number is 12 ÷ 15 × 100 = 80.
Percentage change versus percentage points
If an interest rate goes from 4% to 5%, it has risen by 1 percentage point, but by 25 percent relative to where it started. Mixing these up is one of the most common mistakes with percentages, so the calculator labels changes clearly.
Rounding
Results are shown with up to four decimal places and trailing zeros removed. Copy the value if you need to round it a particular way for a report or invoice.
Frequently asked questions
How do I calculate a percentage of a number?
Multiply the number by the percentage and divide by 100. For example, 25% of 200 is 200 × 25 ÷ 100 = 50.
How do I calculate percentage increase?
Subtract the original value from the new value, divide by the original value, then multiply by 100. Choose "Percentage change" to do this automatically.
Why is a 50% increase followed by a 50% decrease not the original number?
Each percentage applies to a different starting value. 100 increased by 50% is 150, and 150 decreased by 50% is 75.
Can I use negative numbers?
Yes. Negative values work in every mode. Percentage change from zero is undefined, so the calculator will tell you when that happens.
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