Percentage Calculator
This free percentage calculator handles the three percentage problems people look up most: finding X% of Y, working out what percent X is of Y, and measuring percent increase or decrease. Type your numbers and every answer updates instantly, with the worked formula shown step by step.
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How to use this calculator
Start by choosing the kind of percentage problem you're solving with the buttons above the fields. "What is X% of Y?" is for taking a cut of something — a discount, a tip, a tax. "X is what % of Y?" compares a part to a whole — your test score, your savings rate, a click-through rate. "Percent change A → B" measures growth or decline between two values, like a price rise or a shrinking balance.
Enter your numbers and the answer appears instantly — there's no need to press anything. Switch modes freely; your last entered values stay put so you can experiment with the same numbers in each mode.
Every answer comes with the full worked formula, so you can see exactly how the result was reached and copy the method into your homework, spreadsheet, or budget.
How it works
What is X% of Y? The word "percent" means "per hundred," so the formula converts the percentage to a decimal and multiplies: result = (X ÷ 100) × Y. For example, 20% of 150 = 0.2 × 150 = 30.
X is what % of Y? This flips the idea around: divide the part by the whole, then multiply by 100 to express the ratio as a percent: result = (X ÷ Y) × 100. So 30 out of 150 is (30 ÷ 150) × 100 = 20%. Note that Y can't be zero, since division by zero is undefined.
Percent change from A to B compares the difference between the two values against the starting point: result = (B − A) ÷ |A| × 100. A positive answer is an increase and a negative one is a decrease. From 80 to 100 that's (100 − 80) ÷ 80 × 100 = +25% (an increase of 25%), while 100 to 80 gives −20% (a decrease of 20%). Using the absolute value of A keeps the sign correct even if the starting value is negative. Percent change from a starting value of zero is undefined, since there's no base to compare against.
Frequently asked questions
How do I calculate a percentage?
Divide the part by the whole and multiply by 100. For example, 30 out of 150 is (30 ÷ 150) × 100 = 20%.
What is the percent increase formula?
Percent increase = (new value − old value) ÷ old value × 100. For example, going from 80 to 100 gives (100 − 80) ÷ 80 × 100 = 25%.
What is 20% of 150?
30. Convert 20% to the decimal 0.2 and multiply by 150: 0.2 × 150 = 30.
What's the difference between percent and percentage points?
Percent describes relative change; percentage points describe the absolute difference between two percentages. If a rate rises from 20% to 25%, it rose 5 percentage points — which is a 25% relative increase.