How to Calculate Percentages
A percentage is a number expressed as a fraction of 100. The word comes from the Latin per centum, meaning "by the hundred." Percentages are used everywhere — from calculating discounts and tax, to measuring growth rates, exam scores, and salary increases.
Formula: What is X% of a number?
To find a percentage of a number, multiply the number by the percentage and divide by 100.
Result = (Percentage ÷ 100) × Number
Example: What is 20% of 150? → (20 ÷ 100) × 150 = 30
Formula: What percentage is X of Y?
To find what percentage one number is of another, divide the first by the second and multiply by 100.
Percentage = (X ÷ Y) × 100
Example: What percentage is 30 of 150? → (30 ÷ 150) × 100 = 20%
Formula: Percentage Increase or Decrease
To calculate the percentage change between two values, subtract the old value from the new, divide by the old value, and multiply by 100. A positive result is an increase, a negative result is a decrease.
% Change = ((New Value − Old Value) ÷ Old Value) × 100
Example: Price went from £80 to £100 → ((100 − 80) ÷ 80) × 100 = 25% increase
Common Percentage Examples
% increase: 100 to 120
20% increase
% decrease: 200 to 160
20% decrease
Frequently Asked Questions
How do I calculate a percentage of a number?
Multiply the number by the percentage, then divide by 100. For example, to find 20% of 150: (150 × 20) ÷ 100 = 30. Or use the calculator above — enter 20 in the first field and 150 in the second.
How do I calculate percentage increase?
Subtract the old value from the new value, divide by the old value, then multiply by 100. Example: From 100 to 125 → ((125 − 100) ÷ 100) × 100 = 25% increase.
What is the difference between percentage increase and percentage change?
They use the same formula. Percentage change is the general term — if the result is positive, it's an increase. If negative, it's a decrease. Our calculator labels them separately for clarity.
How do I add a percentage to a number?
Multiply the number by (1 + percentage/100). For example, to add 20% to 100: 100 × 1.20 = 120. This is useful for calculating prices with tax or markup added.
How do I calculate a discount?
Use the "Subtract a Percentage" calculator above. Enter the original price and the discount percentage. For example, 20% off £150: 150 − (150 × 0.20) = £120. Or try our dedicated
Discount Calculator.
What is 1% of a number?
Simply divide the number by 100. For example, 1% of 500 = 5. This is a useful mental math trick — once you know 1%, you can easily find any percentage by multiplying.