Understanding your result
The result follows the calculation mode you selected. “What is X% of Y?” returns an amount. The other two modes return a percentage.
For a price reduction, the Discount Calculator also calculates the sale price and tax.
For coursework, the Grade Calculator combines scores using points or category weights.
To calculate with exact fractional parts, use the Fraction Calculator to add, subtract, multiply, or divide fractions.
The formula
To find a ratio, divide the part by the whole and multiply by 100. For percentage change, use (new − original) ÷ |original| × 100. A positive change is an increase; a negative change is a decrease.
What is 15% of 240?
Divide 15 by 100 to get 0.15, then multiply by 240. The answer is 36. If this is a 15% discount on an item priced at 240, subtract 36 from 240 to get a sale price of 204.
How to use this calculator
- Choose a calculation mode.
- Enter the two numbers. The field labels change to match your selection.
- Select Calculate to see the result. Reset restores the example values.
Three questions, three different calculations
Finding a percentage of a number gives you a portion of a total: a discount, a tip, or the amount represented by a rate. Finding what percentage one number is of another describes their relative size.
Percentage change compares a new value with an original value. Going from 80 to 100 is a 25% increase, but going from 100 to 80 is a 20% decrease. The original value determines the denominator.
Percentages and percentage points
A rate moving from 10% to 15% rises by 5 percentage points. Its relative increase is 50%, because the difference of 5 is half of the original 10. Specify which measure you mean when comparing rates.
Successive percentage changes multiply rather than add. A 20% increase followed by a 20% decrease leaves 96% of the starting amount.
Assumptions & limitations
What this calculation assumes
- Numbers use a period as the decimal separator.
- For negative starting values, percentage change uses the absolute value of the original as the denominator.
What to keep in mind
- A ratio with a zero whole and a change from zero are undefined.
- Negative starting values can make percentage comparisons misleading; consider the absolute difference as well.
- Results are rounded for display. Very small and very large results use scientific notation.
Common questions
How do I calculate a discount?
Use “What is X% of Y?” with the discount rate as X and the original price as Y. Subtract the result from the original price.
Can a percentage be greater than 100?
Yes. A percentage over 100 means the part is larger than the reference whole. For example, 150 is 150% of 100.
Why can’t I calculate a percentage change from zero?
Percentage change divides by the original value. Division by zero is undefined, so use the absolute increase instead.