Percentage Calculator

What is a percentage?

A percentage is a way of expressing a number as a fraction of 100. The word comes from the Latin "per centum," meaning "by the hundred." Percentages make it easy to compare proportions — saying a tax rate is 25% is more intuitive than saying it is one quarter, and far more precise than saying it is "about a quarter."

Percentages are used everywhere in daily life: sales tax, discounts, interest rates, exam scores, battery levels, nutrition labels, and statistical data. Understanding how to calculate percentages quickly is one of the most practical math skills you can have.

How to calculate percentages

• X% of Y: Multiply Y by X and divide by 100. Example: 15% of 80 = 80 multiplied by 15 divided by 100 = 12.
• X is what % of Y: Divide X by Y and multiply by 100. Example: 12 is what % of 80 = (12/80) multiplied by 100 = 15%.
• Percentage change: (New minus Old) divided by the absolute value of Old, multiplied by 100. A positive result is an increase; negative is a decrease.
• Add or subtract a percentage: For a 20% increase, multiply by 1.20. For a 20% decrease, multiply by 0.80.

How to use this tool

Select the type of calculation you need from the options provided. Enter the known values and the result appears instantly. The calculator handles all four common percentage operations: finding a percentage of a number, finding what percentage one number is of another, percentage increase/decrease, and adding or subtracting a percentage.

Common percentage examples

• Restaurant tip: 18% of $45 = $8.10, making the total $53.10.
• Sales tax: $100 item plus 8% tax = $108.
• Discount: $80 item with 25% off = $60.
• Salary raise: $50,000 salary with a 5% raise = $52,500.

Common percentage mistakes

The most common error is confusing percentage points with percentages. If interest rates rise from 5% to 7%, that is a 2 percentage point increase but a 40% relative increase. Another common mistake is applying percentage increases and decreases asymmetrically — a 50% increase followed by a 50% decrease does not return to the original value (100 becomes 150, then 75).

Frequently asked questions

How do I calculate a percentage in my head?

Break the calculation into easier steps. To find 15% of a number, calculate 10% (move the decimal point left) and add half of that (5%). So 15% of 80: 10% is 8, half of 8 is 4, and 8 + 4 = 12.

What is the difference between margin and markup?

Markup is the percentage added to cost to get the selling price (based on cost). Margin is the percentage of the selling price that is profit (based on revenue). A 50% markup on a $100 item gives a $150 price. The margin on that same sale is 33.3% ($50 profit / $150 revenue).