How to use the percentage calculator
- Find the calculator card that matches your question, for example “What is X% of Y?” or “Percentage change from X to Y”.
- Type your two numbers. The answer updates as you type.
- Check the formula line under each answer to see exactly how it was calculated.
- Copy an answer or share a link with your numbers filled in.
Worked example
Common percentage questions
15% of 200 is 30. 30 is 15% of 200. Going from 80 to 100 is a 25% increase. 200 increased by 15% is 230, and if 230 is the price after a 15% increase, the original was 200.
How it works
X% of Y = X ÷ 100 × Y. X as a percent of Y = X ÷ Y × 100. Percentage change = (new − old) ÷ |old| × 100. Increase by X% = Y × (1 + X ÷ 100); decrease = Y × (1 − X ÷ 100). Reverse percentage: original = result ÷ (1 + X ÷ 100). Percentage difference = |A − B| ÷ ((A + B) ÷ 2) × 100.
Assumptions
- Results are shown to up to 6 decimal places.
- Division by zero is reported as undefined rather than a number.
Frequently asked questions
Why is a 20% decrease not undone by a 20% increase?
The percentages apply to different bases. 100 minus 20% is 80; 80 plus 20% is 96. To get back to 100 from 80 you need a 25% increase.
What is the difference between percentage change and percentage difference?
Percentage change has a direction (from an old value to a new one). Percentage difference compares two values without a direction, using their average as the base.
How do I remove tax from a price?
Use the reverse percentage card: enter the price including tax and the tax rate as the percentage change. The result is the price before tax.
What is a percentage point?
The simple difference between two percentages. Going from 10% to 12% is a 2 percentage point rise, which is a 20% relative increase.
Limitations
- General arithmetic only; for money with rounding rules such as tax invoices, round the result as your rules require.