Instant percentage calculator with step-by-step working
Calculate percentage of a number, percentage change, and proportions instantly. Fast, free, reactive calculations with full mathematical working.
How it works
Choose calculation mode
Select whether to find a percentage of a number, percentage change, or reverse percentage.
Enter numbers
Type your values into the interactive fields. Results update dynamically in real time.
Review worked steps
Inspect the mathematical formula and substitution steps displayed below the answer.
It is processed on your machine
This is the kind of content people are most nervous about pasting into a website. Here nothing is transmitted: your browser reads the input, the tool works on it in the tab, and the result is handed straight back. Close the tab and it is gone.
- Opened from your disk by your browser — not sent anywhere first.
- Held in the tab while the tool works, then dropped.
- Saved to your device by your browser, not by a link to a server.
- Closing the tab clears the working copy completely.
- No account, so nothing is ever attached to an identity.
- No tracking of what you worked on or what was inside the file.
There is no queue and no retention policy to read. Whatever you pasted is released the moment the tab closes. See how your data stays inside the tab for the full picture, or follow the DevTools check to verify your file never leaves.
What people use it for
Formats & limits
What this tool accepts, what it produces, and what it will never ask you for.
- Input
- The formats listed above
- Output
- Set in the controls above
- Maximum file size
- Set by your device, not by a plan
- Files per run
- One at a time
- Sign-up required
- None
- Watermark
- Never added
- Works offline
- Yes, once the page has loaded
- Supported browsers
- Any current Chrome, Edge, Firefox or Safari
When something goes wrong
Invalid input stops with a plain message that points at the exact problem, rather than a spinner that never finishes.
The content is not in the shape this tool expects. Check for a missing bracket or an extra character and try again.
Why not an online service
A hosted version of this tool means your input is transmitted to a server you have no relationship with. Removing that step removes the whole category of risk.
A typical upload site
This tool
Questions
How do I calculate what percentage one number is of another?
Divide the first number by the second number and multiply by 100. For example, 25 of 200 is (25 / 200) * 100 = 12.5%.
How is percentage increase or decrease calculated?
Subtract the original value from the new value, divide by the absolute original value, and multiply by 100.
Does this calculator upload my numbers?
No. All math runs entirely in your browser using client-side JavaScript. No data is sent to any server.
Can I use decimal values or negative numbers?
Yes. Decimal and negative values are fully supported across all calculation modes.
Is there a file size limit?
No fixed limit is imposed by the tool. The practical ceiling is how much memory your device has free, because the whole job runs inside this browser tab.
Does it work without an internet connection?
Yes, once the page has loaded. Nothing is fetched while you work, so a dropped connection does not interrupt a run.