Rex says
The fast lane for the math you almost remember from school. Type the numbers, get the answer, move on with your day.
Try a scenario
Click to load — tweak from there.Inputs
Result
X% of Y
50.00
X is what % of Y
12.50%
% change from X to Y
700.00%
Psst — share this and help Rex grow
One click, a permanent link with your numbers baked in.
How to use this
- 1Enter x.
- 2Enter y.
- 3Read your x% of y on the right — it updates as you type.
- 4Hit Share to keep the scenario or send it to someone.
About this calculator
Three common percentage operations in one place — handy for tips, discounts, growth rates, and quick math.
Worked example
Using the values the calculator loads with:
Inputs
- X: 25
- Y: 200
Results
- X% of Y: 50
- X is what % of Y: 12.50%
- % change from X to Y: 700.00%
What each field means
Inputs
- X
- The x used in the calculation. Starts at 25 so you have a working example on load.
- Y
- The y used in the calculation. Starts at 200 so you have a working example on load.
Results
- X% of Y
- Returned as a decimal number and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- X is what % of Y
- Returned as a percentage. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- % change from X to Y
- Returned as a percentage. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
How does the percentage calculator work?
Three common percentage operations in one place — handy for tips, discounts, growth rates, and quick math.
What do I need to enter?
2 values: x, and y. Each field starts with a sensible default, so you can change one number at a time and watch the result move.
What does the x% of y result mean?
It is returned as a decimal number and updates live as you edit the inputs, so you can compare two or three versions of a scenario in a few seconds.
Is this calculator free, and do I need an account?
Yes, it's free, and no account is required. Nothing you type is stored on our servers — the maths runs entirely in your browser.
How accurate is the result?
It applies the standard formula exactly, so the arithmetic is precise. Results are rounded for display; the underlying calculation keeps full precision.
Who is this tool for?
It's built for students, developers, and anyone who needs the answer right now without setting up a spreadsheet.
Accuracy and limitations
- Results are rounded for display; the underlying calculation keeps full precision.
- Very large or very small inputs may hit floating-point limits in the browser.
- Inputs outside the accepted range are clamped rather than rejected.
Related tools
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). Percentage Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/percentage
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/percentage" target="_blank" rel="noopener">Percentage Calculator — RevenueLab</a> (2026).</p>
Source: [Percentage Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/percentage) (2026).