Percentage calculator
Work out a percent of a number, what percent one number is of another, and percent change in your browser.
The numbers you type stay in this browser and are not uploaded.
Numbers you type never leave this device.
How to use it
- 1
Pick the question you have
Use the first box for a percent of a number, the second for a share, and the third for a change between two values.
- 2
Type the two numbers
Fill both boxes of that calculator. Decimals such as 12.5 and negative numbers such as -40 work, and thousands commas like 1,200 are accepted.
- 3
Read the result
The answer appears under the boxes with no button to press. A rise in percent change is shown with a plus sign.
- 4
Change a number to compare
Edit either box to see a new answer at once. Nothing is saved, so closing the tab clears every number you typed.
Common use cases
Security and privacy
Your numbers stay on your device
Every calculation is done by browser code on your device while you type. No upload route exists for this tool, no request carries your numbers, and nothing is stored after you close the tab. You can enter private prices or figures without sending them to anyone.
Supported inputs and outputs
What it calculates
- Y percent of a number X
- What percent a number X is of a number Y
- Percent change from a starting value to a new value
- Results shown to ten significant digits
FAQ
Are my numbers uploaded?
No. The calculation runs inside your browser. No request that carries your numbers is sent to Frisbly or anyone else.
How is percent change calculated?
It is the new value minus the starting value, divided by the starting value, times 100. Going from 80 to 100 is a 25% rise, and going from 100 to 80 is a 20% drop. If the starting value is negative, its size without the sign is used.
Why does it say I cannot divide by zero?
A share needs a whole that is not zero, and a percent change needs a starting value that is not zero. Change the number that is 0 to get an answer.
Why is a percent change not the same in both directions?
Each change is measured against its own starting value. Rising from 80 to 100 is 25%, but falling back from 100 to 80 is 20%, because the starting value is different.
How many digits are shown?
Results are rounded to ten significant digits, which hides tiny computer rounding noise such as 0.30000000000000004 while keeping useful precision.