Overview
Switch between the three percentage calculations people actually reach for: finding X% of a number, figuring out what percent one number is of another, and computing the percent change (increase or decrease) between two values. Each mode shows the exact formula being applied above the result - like "(20 / 100) × 150" - so the answer isn’t a black-box number but something you can verify by hand or learn from. The percent change mode uses the original value’s absolute value in the denominator, which is the standard convention that keeps the sign of the result meaningful (positive for an increase, negative for a decrease) even when the original value itself is negative. Runs entirely client-side.
Best for: Calculating a discount or year-over-year change
How to use this tool
- Choose a calculation mode. X% of Y, X is what % of Y, or % change from X to Y.
- Enter your two numbers. The fields relabel themselves to match what each mode expects.
- See the formula used. The exact calculation, like "(20 / 100) × 150," is shown above the result.
- Read the answer. The result updates live as you type either number.
Why use this tool
Three modes in one tool
Covers the three percentage questions people actually ask, without needing three separate calculators.
Shows its work
The formula is displayed above every result, so it’s a learning aid, not just a black-box number.
Correct sign handling
Percent change uses the original value’s absolute value, keeping increase/decrease signs meaningful.
Live results
No calculate button - the answer updates as soon as you finish typing either number.
Frequently asked questions
"X% of Y" answers a question like "what is 20% of 150?" - you already know the percentage and want the resulting amount. "X is what % of Y" answers the reverse question, like "30 is what percent of 150?" - you know two actual amounts and want to find the percentage relationship between them. They use different formulas and solve for different unknowns, which is why they’re kept as separate modes rather than one combined calculator.
A negative result means the value decreased from X to Y - for example, going from 200 to 150 is a -25% change. The formula divides by the absolute value of the original number specifically so the sign of the result always reflects the direction of the change (decrease vs. increase) rather than flipping unpredictably when the original value itself happens to be negative.