Percentage Calculator Online
Find X% of Y, work out what percent one number is of another, or measure percent change, right in your browser.
The Percentage Calculator runs entirely in your browser. The numbers you enter never leave your device and nothing is uploaded to ArrayKit.
Open the Fraction Calculator
About Percentage Calculator
The Percentage Calculator solves the three percentage problems people run into most often. Use X% of Y to find a portion of a number, such as a discount or a tip. Use X is what % of Y to see what share one number represents of another, like a test score or a budget line. Use Percent change to measure the increase or decrease between two values, such as a price, a metric, or a measurement over time. Each mode takes two numbers and shows the answer along with a worked line so you can see exactly how the result was reached. It is built for students checking homework, shoppers comparing discounts, and analysts sanity-checking a quick figure. Everything runs locally in your browser — no numbers are uploaded.
Features
- Three modes: X% of Y, X is what % of Y, and percent change
- Instant results as you type, with a worked line showing the calculation
- Handles negative numbers and percentages over 100%
- Percent change mode labels the result as an increase or decrease
- One-click copy of the result or the full worked line
- Clear error messages for invalid or zero-division input
- Rounded, readable output with thousands separators
- Runs entirely in your browser with no numbers sent anywhere
How to use the Percentage Calculator
- Pick a mode: X% of Y, X is what % of Y, or Percent change
- Enter the two known numbers for that mode
- Read the result and the worked line underneath
- Copy the result or the worked line with one click
Example
Input
20% of 150
Output
30
20% of 150 = (20 / 100) × 150 = 30.
Common errors & troubleshooting
- Percent change mode shows an error when the starting value is 0. — Percent change divides by the starting value, so it is undefined when that value is 0. Use X% of Y instead if you just need a portion of a number.
- Result looks wrong after typing a rate like 0.2 instead of 20. — Enter the percent as a whole number (20 for 20%), not a decimal fraction (0.2). The Percentage Calculator multiplies by percent ÷ 100 for you.
- Percent change shows a negative number when the value went up. — Check which field is 'From' and which is 'To' — a negative result means the 'To' value is smaller than the 'From' value, i.e. a decrease.
- 'X is what % of Y' shows an error with a whole of 0. — You cannot divide by a whole of 0. Enter a non-zero denominator, or switch to X% of Y if that fits your problem better.
Frequently asked questions
- What is the Percentage Calculator?
- It is a browser tool with three modes for common percentage problems: finding X% of Y, finding what percent one number is of another, and finding the percent change between two values.
- How does the Percentage Calculator find X% of Y?
- It multiplies Y by X divided by 100, so 20% of 150 becomes (20 / 100) × 150 = 30. The worked line under the result shows this calculation.
- How is percent change calculated?
- Percent change is ((new value − old value) / old value) × 100. A positive result is an increase and a negative result is a decrease, and the tool labels which one it is.
- Can the Percentage Calculator handle percentages over 100%?
- Yes. Values above 100% and negative numbers are all supported, so you can calculate things like 250% of a number or a percent decrease below zero.
- Does the Percentage Calculator round its answers?
- Results are rounded to two decimal places for readability. The copy button gives you the same rounded value so it matches what is shown on screen.
- Is my data sent anywhere when I use the Percentage Calculator?
- No. The Percentage Calculator runs entirely in your browser. The numbers you type never leave your device and are not uploaded to ArrayKit.
Related tools
All ArrayKit tools