Percentage Calculator
Calculate X% of Y, what percent X is of Y, percentage increase/decrease, or percentage difference — with the formula and substitution shown.
Calculated entirely in your browser — nothing you enter here is sent to a server.
Percentage increase/decrease and percentage difference are often confused but answer different questions. Increase/decrease compares a new value back to a specific starting point (order matters: going from 50 to 75 is a 50% increase, but going from 75 back to 50 is a 33.3% decrease, not 50%). Percentage difference instead compares two values to each other with no notion of which came first, using their average as the base.
A percentage change from a starting value of zero, or a percentage of zero, is mathematically undefined — this calculator reports that clearly instead of showing a meaningless Infinity or NaN.
The four percentage formulas
- X% of Y:
(X ÷ 100) × Y. 15% of 240 is 36. - X is what percent of Y:
(X ÷ Y) × 100. 45 is 25% of 180. - Percentage change:
(new − old) ÷ |old| × 100. From 50 to 65 is a 30% increase. - Percentage difference:
|A − B| ÷ ((|A| + |B|) ÷ 2) × 100. 50 and 65 differ by 26.09%, whichever comes first.
Common percentage mistakes
- Increases and decreases don't cancel out. 100 raised by 20% is 120; 120 cut by 20% is 96, not 100, because the second percentage applies to a bigger number.
- Percent vs percentage points. A rate rising from 4% to 5% has gone up 1 percentage point, which is a 25% increase. Say which one you mean.
- Finding the original before an increase. Divide instead of subtracting: a price of 120 that includes 20% tax was 120 ÷ 1.2 = 100 before tax, not 120 − 20% = 96.
- Use percentage change when there is a clear before and after, and percentage difference when comparing two values on an equal footing.
How to use the Percentage Calculator
- Choose a Calculation: X% of Y, X is what % of Y, % increase/decrease, or % difference between two values.
- Fill in the two fields; their labels change to match the calculation (for example Old value and New value).
- Click Calculate to see the result, the formula used, and the formula with your numbers substituted.
- Click Reset to clear both fields and the result.
Example: A price drop from 80 to 60
Choose % increase/decrease, enter 80 as Old value and 60 as New value, and click Calculate. The result is -25%, with the formula % change = ((New − Old) ÷ |Old|) × 100 and the substitution ((60 − 80) ÷ |80|) × 100 = -25.
Questions about the Percentage Calculator
- Why does the big result show fewer decimals than the substitution line?
- The main result is rounded to at most four decimal places for readability, while the substitution line shows the full unrounded value. For example, 1 is what % of 3 displays 33.3333% above (1 ÷ 3) × 100 = 33.33333333333333.
- How are negative starting values handled in % increase/decrease?
- The change is divided by the absolute value of the old value, so the sign of the result always follows the direction of the move. Going from -50 to -25 is reported as a 50% increase.
- Why is the X% of Y result shown without a percent sign?
- That calculation returns an amount, not a percentage: 15% of 80 is 12. The other three calculations return percentages and are shown with a % sign.
- Can I enter decimals or negative numbers?
- Yes, all four calculations accept decimals and negative numbers. The only inputs rejected are empty fields and the zero cases that would divide by zero.
- How do I calculate a percentage increase?
- Subtract the old value from the new one, divide by the old value and multiply by 100. Going from 50 to 65 is (65 − 50) ÷ 50 × 100 = a 30% increase. Choose % increase/decrease in the calculator to do this.
- What is the difference between percentage change and percentage difference?
- Percentage change measures movement from a starting value, so the order matters. Percentage difference compares two values against their average, so the order doesn't: 50 and 65 differ by 26.09% either way, while 50 → 65 is a 30% increase and 65 → 50 a 23.08% decrease.