How to Calculate a Percentage
Use the formula (part ÷ whole) × 100 to find what percentage one number is of another. To find a percentage of a number, use number × percentage ÷ 100.
Percentage calculator
Percentage formulas at a glance
Find X% of a number
number × percentage ÷ 100
20% of 150 = 150 × 20 ÷ 100 = 30.
Find what percent X is of Y
part ÷ whole × 100
45 is what percent of 180? 45 ÷ 180 × 100 = 25%.
Find the whole from a percentage
part ÷ (percentage ÷ 100)
30 is 20% of what number? 30 ÷ 0.20 = 150.
How do you calculate a percentage of a number?
Convert the percentage to a decimal by dividing it by 100, then multiply by the number. For example, to find 15% of 240:
- 15 ÷ 100 = 0.15
- 0.15 × 240 = 36
- So, 15% of 240 is 36.
The shortcut is the same calculation written as 240 × 15 ÷ 100 = 36.
How to calculate percentage increase or decrease
Use the original value as the denominator:
If a price rises from $80 to $100, the difference is $20. Divide 20 by 80 and multiply by 100: 25% increase.
If a price falls from $100 to $80, the difference is −$20. Relative to the original $100, that is a 20% decrease.
How to add or subtract a percentage
To increase a number by p%, multiply it by 1 + p/100. To decrease it by p%, multiply by 1 − p/100.
Add 15% to $80: $80 × 1.15 = $92.
Take 20% off $75: $75 × 0.80 = $60.
How to calculate a reverse percentage
When you know the final value after a percentage increase or decrease, divide by the multiplier instead of simply subtracting the percentage.
Example: a price is $120 after a 20% increase. The original price was $120 ÷ 1.20 = $100.
For a decrease, use final ÷ (1 − p/100). If a $72 price is the result of a 10% discount, the original price was $72 ÷ 0.90 = $80.
Percentage vs. percentage points
Percentage points describe the arithmetic difference between two percentages. Relative percentage change compares that difference with the starting percentage.
If a rate moves from 5% to 6%, it rises by 1 percentage point. Relative to 5%, however, the increase is 20%: (6 − 5) ÷ 5 × 100.
Common percentage mistakes
Using the wrong base
For percent change, divide by the original value, not the new value.
Assuming opposite changes cancel
+20% and −20% use different bases, so they do not cancel each other.
Confusing percent with percentage points
A move from 10% to 12% is +2 percentage points, but a 20% relative increase.
Percentage examples in everyday life
Discount
A $120 jacket with 25% off has a $30 discount: 120 × 0.25 = 30. Final price: $90.
Tip
An 18% tip on a $50 bill is 50 × 0.18 = $9. Total: $59.
Test score
42 correct answers out of 50 is 42 ÷ 50 × 100 = 84%.
Sales tax
At an example 8% tax rate, tax on $75 is 75 × 0.08 = $6. Total: $81.
Conversion rate
36 purchases from 1,200 visits is 36 ÷ 1,200 × 100 = 3%.
Growth
Moving from 200 to 250 is (250 − 200) ÷ 200 × 100 = 25% growth.
Sources & methodology
AskNelu calculates percentages directly from the formulas shown on this page. NIST describes the percent symbol as representing 0.01 — parts per hundred. For percentage change, the U.S. Bureau of Labor Statistics describes the standard sequence as subtracting the earlier value from the later value, dividing by the earlier value, then multiplying by 100.
Examples are illustrative arithmetic, not financial, tax, or legal advice. Actual tax rates and other real-world percentages vary by jurisdiction and situation.
Explore percentage calculations
Percentage increase
Measure growth from an original value.
Percentage decrease
Measure a reduction from an original value.
Reverse percentage
Work backward to the original value.
Percentage points
Compare point change with relative percent change.
Source & methodology
NIST defines the percent symbol as representing the number 0.01.
Frequently asked questions
What is the easiest way to calculate a percentage?
For X% of a number, multiply the number by X and divide by 100. For example, 10% of 250 is 250 × 10 ÷ 100 = 25.
How do I calculate what percentage one number is of another?
Divide the part by the whole and multiply by 100. For example, 30 out of 120 is 30 ÷ 120 × 100 = 25%.
How do I calculate a 20% increase?
Multiply the original value by 1.20. A value of 50 increased by 20% is 60.
How do I calculate a 20% discount?
Multiply the original price by 0.80. An $80 item discounted by 20% costs $64.
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