Below is a percentage calculator that handles the six most common percentage problems. Find the percentage of a number, figure out what percent one number is of another, calculate percent change between values, apply discounts, compute percent error for lab work, and even find a percentage of a percentage.
Percentage calculator
Using the percentage calculator
Select a calculation type using the buttons at the top, enter your numbers, and see results instantly. The tool updates as you type - no need to click a calculate button.
% of Number (default)
The most common percentage question: What is X% of Y? Enter a percentage and a number, and the tool multiplies them for you. Use this for tips, tax calculations, or finding any fraction of a total.
Example: What is 15% of 200? Answer: 30
What %?
The reverse question: X is what percent of Y? Enter a part and a whole, and the tool calculates the percentage. Perfect for test scores, completion rates, or understanding proportions.
Example: 45 is what percent of 180? Answer: 25%
% Change
Calculate the percent increase or decrease between two values. Enter a starting value and a final value, and the tool shows the percentage change with a directional indicator (↑ increase or ↓ decrease).
Example: From 100 to 125 is a 25% increase
For more specialized needs, see our dedicated Percent Change Calculator, Percent Increase Calculator, or Percent Decrease Calculator.
% Off
The shopping discount mode. Enter an original price and a discount percentage, and the tool shows the final price after the discount plus how much you save. Works for any sale, coupon, or markdown.
Example: $100 at 20% off = $80 (you save $20)
% Error
For science labs and quality control. Enter your measured value and the actual (or expected) value, and the tool calculates the percent error - how far off your measurement was as a percentage of the true value.
Example: Measured 105 when actual was 100 = 5% error
% of %
A less common but sometimes confusing calculation: What is X% of Y%? This converts the first percentage to a decimal and multiplies by the second percentage. Useful for compound discounts, probability, and multi-step percentage problems.
Example: 25% of 80% = 20%
We also have a dedicated Percentage of Percentage Calculator if you need more detail on this calculation.
The percentage formula
A percentage is a fraction of 100. The word itself comes from Latin per centum, or "by the hundred."
\text{Percentage} = \frac{\text{Part}}{\text{Whole}} \times 100To find a percentage of a number, convert the percentage to a decimal (divide by 100) and multiply:
15\% \text{ of } 200 = \frac{15}{100} \times 200 = 0.15 \times 200 = 30Percent change uses a similar approach - find the difference, then divide by the original:
\text{Percent Change} = \frac{\text{New Value} - \text{Original Value}}{\text{Original Value}} \times 100And percent error measures accuracy - the absolute difference divided by the actual value:
\text{Percent Error} = \frac{|\text{Measured} - \text{Actual}|}{|\text{Actual}|} \times 100Related calculators
For more specialized percentage and fraction conversions:
