Percentage Calculator
What is X% of Y? Percentage change, increase, decrease — all in one tool.
This calculator handles the three percentage problems you'll ever meet: finding X% of a number (discounts, tips, tax), working out what percent one number is of another (test scores, proportions), and measuring the percentage change between two values (price rises, salary increases). Type your numbers and results appear instantly.
The formulas behind the tool
X% of Y = (X ÷ 100) × Y. X as a percent of Y = (X ÷ Y) × 100. Change from A to B = ((B − A) ÷ A) × 100. That last divisor — the original value — is where most manual mistakes happen, which is exactly why this tool exists.
Want to master the mental math?
Percentages are very learnable. Our guide Percentages Made Simple teaches the 10% shortcut, the "X% of Y = Y% of X" flip trick, and the reversal trap that catches almost everyone.
Frequently asked questions
How do I calculate a percentage of a number?
Divide the percentage by 100 and multiply by the number. For example, 25% of 80 is (25 ÷ 100) × 80 = 20.
How do I work out percentage increase?
Subtract the old value from the new value, divide by the old value, and multiply by 100. Going from 50 to 65 is ((65 − 50) ÷ 50) × 100 = a 30% increase.
Why doesn’t a 20% increase then 20% decrease cancel out?
Because the decrease is applied to a larger number. 100 plus 20% is 120; 120 minus 20% is 96. Percentage changes are always relative to the current value, not the original.
Can I use this for discounts and tips?
Yes — use the "X% of Y" mode. For a 30% discount on $45, calculate 30% of 45 ($13.50) and subtract it, or calculate 70% of 45 directly to get the final price.