Percentage Calculator
Calculate percentages, find what % one number is of another, and compute % change.
How to Use
- Choose a mode: "X% of Y", "X is what % of Y?", or "% Change".
- Enter your values in the input fields.
- The result updates instantly — no need to click Calculate.
- Switch between modes anytime without losing your inputs.
When to Use This
- Checking a quoted markup: enter the old and new price in change mode to see whether a supplier's increase matches the figure they stated.
- Grading a test where the total marks differ from 100, since the second mode turns a raw score out of any denominator into a percentage.
- Working out a tip or a commission share when the X percent of Y mode is faster than reaching for a phone calculator.
- Comparing two months of traffic or revenue, where the signed change plus the absolute difference gives you the size and the direction at once.
Frequently Asked Questions
About This Calculator
Three questions all get called percentage problems, and they are different operations. Finding X percent of a number is multiplication by X/100. Asking what percentage one number is of another is division. Percentage change divides the difference by the starting value, which is why the relationship is not symmetric: a move from 80 to 100 is a 25 percent increase, while 100 back to 80 is a 20 percent decrease.
Each mode here is a separate panel that recalculates on every keystroke. The change mode divides by the absolute value of the starting number, so a negative baseline still produces a correctly signed result, and it prints the raw difference next to the percentage. Results under 1000 are trimmed to six decimal places, larger numbers get locale thousands separators, and percentages are shown to four. The arithmetic runs in the page itself.
Notes & Limits
- Percentage change needs a non-zero starting value; enter zero as the starting number and the result panel hides rather than reporting an undefined or infinite change.
- Displayed percentages are rounded to four decimal places and plain results to six, so a long repeating decimal is shown truncated rather than exact.
- The three modes are independent panels; a value typed into one is not carried into another, and nothing is saved between page loads.
- This handles one operation at a time. Chaining two steps, such as a markup followed by a discount, means feeding each result back in by hand.