How this works
A percentage is just a fraction with 100 as the denominator — "25%" means 25 out of 100. This calculator handles the three questions people ask most: what is X% of Y, what percentage is X of Y, and how much did a value change in percent. Pick a tab, enter the two numbers, and the answer updates as you type.
The formula
A negative result on the third formula means a decrease; the absolute value in the denominator keeps the sign right when A itself is negative.
Example calculation
- A jacket costs €120 and is on sale at 25% off. What is 25% of 120? (25 / 100) × 120 = €30 saved.
- You scored 42 on a test out of 60. What percentage is that? (42 / 60) × 100 = 70%.
- A stock rose from $80 to $92. What was the % change? ((92 − 80) / 80) × 100 = +15%.
Frequently asked questions
How do I calculate a discount?
Use the "X% of Y" tab. Enter the discount percentage as X and the original price as Y — the result is the amount you save. Subtract that from the original price to get the sale price.
What's the difference between percentage points and percent?
If interest rates rise from 4% to 5%, that's a 1 percentage point increase but a 25% relative increase. This calculator returns the relative percent change in the "% change" tab — fine for most everyday questions; just be careful with rates and probabilities.
How do I work backwards — find the original price before tax?
If a price already includes 20% tax, divide by 1.20 (not by 0.80). Use the "X is what % of Y" tab with the after-tax price as X and 1.20 as Y to verify, or just compute directly: original = total / (1 + rate/100).
Why is "% change" different depending on which value you start from?
A change from 100 to 120 is +20%, but going back from 120 to 100 is −16.7% — not −20%. Percentage change is always relative to the starting value (the denominator). When comparing two periods, be explicit about which one is the baseline.