About this tool
Percentage Calculator
Percentage Calculator handles the four percentage questions people actually ask, each in its own box: what is X percent of Y, X is what percent of Y, percentage change between two numbers, and adding or subtracting a percentage from a number. Every result copies with one click.
How to use it
- Pick the box that matches your question.
- Enter the two numbers.
- Read the answer and press Copy if you need it elsewhere.
The four calculations
Percent of: multiply the number by the percentage and divide by 100. 15 percent of 200 is 200 x 15 / 100 = 30.
Is what percent: divide the part by the whole and multiply by 100. Percentage change: subtract the old value from the new, divide by the old value, multiply by 100. Add or subtract: multiply by (100 plus or minus the percentage) divided by 100.
Worked example
The default values, showing the first two calculations are inverses of each other:
- 15% of 20030
- 30 is what % of 20015%
Result: The same relationship read in both directions, which is the check most percentage errors fail.
When it helps
- Working out a discount or a tax amount.
- Calculating percentage growth between two figures.
- Adding a markup or taking off a discount.
- Checking a figure someone else has quoted.
Common mistakes
- Assuming a percentage increase and decrease cancel out. Add 10% then subtract 10% and you land at 99% of where you started, not 100%.
- Confusing percentage points with percent. Going from 5% to 7% is a rise of 2 percentage points but a 40% increase.
- Using the wrong base for percentage change. The change is always measured against the original value.
