What is X% of Y?
- 200 × 15 ÷ 100 = 30
X is what percent of Y?
- 30 ÷ 200 × 100 = 15%
Percentage change from X to Y
- (75 − 50) ÷ 50 × 100 = 50%
Percentage point difference
- 15% − 10% = 5 percentage points
How to use
- Pick the question you want to answer. Each box on the page handles one type of percentage problem.
- Type your numbers. Commas are fine and results update as you type.
- Read the result and the formula underneath it, which shows exactly how the answer was calculated.
- Copy the formula into a spreadsheet or report if you need to show your working.
Four everyday percentage questions
Percentages appear everywhere: exam scores, tips, tax, sales, interest rates, survey results and business reports. Almost all of them come down to one of four questions, and this page has a calculator for each.
- What is X% of Y? Use it for tips, tax, commission or any share of a total.
- X is what percent of Y? Use it for test scores, completion rates and market share.
- What is the percentage change from X to Y? Use it for price changes, growth rates and year-over-year comparisons.
- What is the difference in percentage points? Use it when both values are already percentages, such as interest rates or election results.
The formulas
- Percent of a number: result = number × percent ÷ 100
- Percent of a total: percent = part ÷ whole × 100
- Percentage change: change = (new − old) ÷ |old| × 100
- Percentage points: points = new rate − old rate
When the old value is negative, the change is divided by its absolute value so that moving from −50 to 50 is reported as an increase of 200% rather than a confusing negative number.
Worked examples
A restaurant bill is $86 and you want to leave an 18% tip: 86 × 18 ÷ 100 = $15.48. A company grew its customers from 1,250 to 1,600: (1,600 − 1,250) ÷ 1,250 × 100 = 28% growth. A savings rate rises from 3.5% to 4%: that is 0.5 percentage points, or a relative increase of about 14.3%.
Common mistakes
The most common error is dividing by the wrong number. Percentage change is always measured against the starting value, not the ending value, so a fall from 75 back to 50 is a 33.3% decrease, not 50%. Another frequent mistake is adding percentages that apply one after another. Two discounts of 20% and 10% do not make 30% off; they make 28% off, because the second discount applies to the already reduced price. The discount calculator handles that case for you.
Finally, be careful with rounding. The calculator keeps full precision internally and rounds only the number it displays, so results stay accurate even when you chain several calculations.
Frequently asked questions
- How do I calculate a percentage of a number?
- Multiply the number by the percentage and divide by 100. For 15% of 200, that is 200 × 15 ÷ 100 = 30. You can also convert the percentage to a decimal first, 0.15 × 200 = 30.
- How do I find what percent one number is of another?
- Divide the part by the whole and multiply by 100. If you scored 42 out of 50, that is 42 ÷ 50 × 100 = 84%.
- How is percentage change calculated?
- Subtract the old value from the new value, divide by the old value and multiply by 100. A price that goes from 50 to 75 has increased by (75 − 50) ÷ 50 × 100 = 50%.
- What is the difference between percent and percentage points?
- Percentage points measure the plain difference between two percentages. An interest rate that moves from 10% to 15% has risen by 5 percentage points, but by 50% relative to where it started. News reports often mix these up.
- Why can't I divide by zero?
- Taking a percentage of zero is valid; for example, 15% of 0 is 0. Division by zero is undefined, so the calculator cannot find what percent a value is of 0 or calculate a percentage change from 0. Enter a nonzero total or starting value for those questions.
- Why does a 50% increase followed by a 50% decrease not return to the start?
- Each change is measured from a different base. 100 plus 50% is 150, and 150 minus 50% is 75. To undo a 50% increase you need a 33.3% decrease.