Percentage Calculator with Step-by-Step Working
Five everyday percentage questions side by side, each answered as you type. Every result shows the formula with your numbers substituted, so you can check it or copy the method.
How to calculate a percentage
- Find the card that matches your question, such as "What is X% of Y?" or "Percentage change".
- Type your two numbers. Commas as thousands separators are fine.
- Read the answer under the inputs. The line below it shows the formula with your numbers.
- For add/subtract, choose whether to increase or reduce the number by the percentage.
Percentage change vs percentage difference
Percentage change has a direction: it compares a new value with an original one, so going from 80 to 100 is a 25% increase but going back from 100 to 80 is a 20% decrease. Percentage difference has no direction: it divides the gap by the average of the two values, so 80 and 100 differ by about 22.2% whichever way round you enter them. Use change for prices over time and difference for comparing two measurements. For tax added on top of a price, the GST Calculator handles inclusive and exclusive amounts.
Benefits
- All five common percentage questions on one screen, so there's no mode to switch.
- Each result shows the formula with your numbers substituted, which makes it easy to check.
- Rounding noise like 0.30000000000000004 is cleaned up, and numbers use your locale's format.
Limitations
- Results use standard double-precision arithmetic, so very large or very precise values are accurate to about 15 significant digits.
- Percentage change from 0 and percentage of a total of 0 are undefined, so the tool reports them as such instead of showing a number.
Privacy and security
Every number you type is calculated by JavaScript in this browser tab. Nothing is sent to a server or saved after you close the page.
Read our privacy policy for details about the site as a whole.
Frequently asked questions
How do I calculate a percentage increase?
Subtract the original value from the new value, divide by the original value and multiply by 100. From 80 to 100: (100 − 80) ÷ 80 × 100 = 25% increase. A negative result is a decrease.
Why doesn't adding 10% and then subtracting 10% give the original number?
The second percentage is taken from a different base. 100 + 10% = 110, but 10% of 110 is 11, so 110 − 10% = 99. To undo a 10% increase, divide by 1.10 instead.
Can I use negative numbers or decimals?
Yes. Any real number is accepted. For percentage change the original value's absolute size is used as the base, so a move from −50 to −25 is reported as a 50% increase.