Percentage Calculator
Calculate percentages three ways: find X% of Y, find what percent X is of Y, and compute percentage change from X to Y
About Percentage Calculator
Overview
Percentage Calculator bundles the three percentage questions people ask most often into one fast, browser-based tool. Switch between "what is X% of Y", "X is what percent of Y", and "percentage change from X to Y" with a single dropdown. Each mode shows clearly labeled inputs, an instant result, and a short worked-out explanation so you can see exactly how the answer was reached. All math runs locally in your browser, so your numbers never leave your device.
Features
- Three percentage modes in one tool: part-of-whole, whole-from-part, and percent change
- Live Mode for instant results as you type
- Color-coded results: blue for neutral, green for increase, red for decrease
- Worked-out explanation with the formula and step-by-step calculation
- Handles decimals, large numbers, negative values, and zero-change cases
- Catches division-by-zero errors with a clear inline message
- Completely browser-based - no data uploaded to servers
- Mobile-friendly responsive design with full dark mode support
How to Use
- Pick a calculation mode from the dropdown (X% of Y, X is what % of Y, or % change from X to Y)
- Enter the two values using the labeled inputs that match the selected mode
- Read the instant result in the Result card
- Open the "How we calculated this" card to see the formula and step-by-step breakdown
- Toggle Live Mode off if you prefer a single explicit Calculate button click
FAQ
What is the difference between the three modes?
The "X% of Y" mode finds a part given a percentage and a whole (for example, 20% of 150 is 30). The "X is what % of Y" mode finds the percentage given a part and a whole (for example, 30 is 20% of 150). The "% change" mode finds how much something grew or shrank from an original value to a new value (for example, going from 80 to 100 is a 25% increase).
Can I enter negative numbers?
Yes. Negative values are valid in all three modes and produce signed results. For example, entering -10 and 200 in "X% of Y" returns -20, and entering 10 and 200 returns 20. The percentage change mode will show a negative percentage when the new value is smaller than the original.
Why does it show an error when Y is zero?
In the "X is what % of Y" and "% change" modes the calculator must divide by Y (or X) to compute the answer. Division by zero is undefined in mathematics, so the tool blocks the calculation and asks for a non-zero value rather than displaying infinity or NaN.
How many decimal places does the result show?
Results are shown with up to 6 significant decimal places, with trailing zeros removed for readability. So 1 divided by 3 displays as 0.333333 in "X% of Y" mode and 33.333333% in "X is what % of Y" mode. The worked-out steps show the same precision so you can verify the answer.
Is my data sent to a server?
No. All calculations happen entirely in your browser using client-side JavaScript. The numbers you type are never transmitted, logged, or stored anywhere. You can use the tool offline once the page has loaded.