How to Calculate Percentage: Formula, Examples & Easy Methods
Knowing how to calculate a percentage is a useful math skill that comes up in everyday life. Percentages are used to calculate discounts, compare numbers, understand test scores, measure increases and decreases, calculate profits, and much more.
The basic percentage formula is:
Percentage = (Part ÷ Whole) × 100
For example, if you scored 45 marks out of 60:
Percentage = (45 ÷ 60) × 100 = 75%
So, your score is 75%.
In this guide, you’ll learn how to calculate a percentage step by step, find what percentage one number is of another, calculate percentage increases and decreases, and solve common percentage problems with easy examples.
What Is a Percentage?
A percentage is a way of expressing a number as a fraction of 100. The word “percent” literally means “per hundred.”
For example:
- 25% means 25 out of 100
- 50% means 50 out of 100
- 75% means 75 out of 100
- 100% means the entire amount
Percentages are represented using the % symbol.
Because percentages are based on 100, they make it easy to compare different quantities.
Percentage Formula
The most common percentage formula is:
Percentage = (Part ÷ Whole) × 100
Where:
- Part is the amount you are comparing
- Whole is the total amount
- 100 converts the result into a percentage
Example
Suppose a class has 40 students and 10 of them are absent. What percentage of students are absent?
Use the formula:
Percentage = (10 ÷ 40) × 100
Percentage = 0.25 × 100
Percentage = 25%
Therefore, 25% of the students are absent.
How to Calculate a Percentage of a Number
Sometimes you may want to find a specific percentage of a number.
For example, what is 20% of 150?
First convert the percentage into a decimal:
20% = 20 ÷ 100 = 0.20
Then multiply it by the number:
0.20 × 150 = 30
Therefore:
20% of 150 = 30
You can also use the formula:
Percentage of a Number = (Percentage ÷ 100) × Number
More Examples
10% of 200
= (10 ÷ 100) × 200
= 20
25% of 80
= (25 ÷ 100) × 80
= 20
15% of 500
= (15 ÷ 100) × 500
= 75
How to Find What Percentage One Number Is of Another
A common percentage problem is finding what percentage one number represents of another.
Use:
Percentage = (First Number ÷ Second Number) × 100
Example
What percentage is 30 of 120?
Percentage = (30 ÷ 120) × 100
Percentage = 25%
Therefore, 30 is 25% of 120.
Another Example
What percentage is 45 of 60?
Percentage = (45 ÷ 60) × 100
Percentage = 75%
Therefore, 45 is 75% of 60.
How to Calculate Percentage Increase
Percentage increase tells you how much a value has increased compared with its original value.
The formula is:
Percentage Increase = [(New Value − Original Value) ÷ Original Value] × 100
Example
A product originally costs $80 and now costs $100. What is the percentage increase?
First find the increase:
$100 − $80 = $20
Then divide the increase by the original price:
$20 ÷ $80 = 0.25
Convert to a percentage:
0.25 × 100 = 25%
Therefore, the price increased by 25%.
How to Calculate Percentage Decrease
Percentage decrease measures how much a value has fallen compared with its original value.
The formula is:
Percentage Decrease = [(Original Value − New Value) ÷ Original Value] × 100
Example
A product’s price falls from $200 to $150.
First calculate the decrease:
$200 − $150 = $50
Then:
($50 ÷ $200) × 100 = 25%
Therefore, the price decreased by 25%.
How to Calculate Percentage Change
Percentage change is commonly used when comparing an original value with a new value.
The formula is:
Percentage Change = [(New Value − Original Value) ÷ Original Value] × 100
For example, if a value changes from 50 to 65:
[(65 − 50) ÷ 50] × 100
= (15 ÷ 50) × 100
= 30%
The value increased by 30%.
If the new value is lower than the original value, the result will be negative, indicating a decrease.
Quick Percentage Examples
Here are some common percentage calculations:
| Calculation | Answer |
|---|---|
| 10% of 100 | 10 |
| 20% of 150 | 30 |
| 25% of 200 | 50 |
| 50% of 80 | 40 |
| 75% of 200 | 150 |
| 15% of 300 | 45 |
| 30 is what percentage of 120? | 25% |
| 45 is what percentage of 60? | 75% |
How to Calculate Percentage Quickly
For simple numbers, you can often calculate percentages mentally.
10%
To find 10%, divide the number by 10.
10% of 250 = 25
50%
50% means half.
50% of 80 = 40
25%
25% means one-quarter.
25% of 200 = 50
1%
To find 1%, divide the number by 100.
1% of 500 = 5
These shortcuts can make everyday percentage calculations much faster.
[cp_inline_calculator type=”percentage”]
Using a Percentage Calculator
For simple calculations, the formulas above are usually enough. However, calculations involving large numbers, decimals, discounts, increases, or multiple steps can be easier with an online tool.
Use the CalculatorPool Percentage Calculator to calculate percentages quickly without doing the math manually.
It can be particularly useful when you need to check a calculation or work with numbers that are difficult to calculate mentally.
Common Percentage Mistakes
1. Forgetting to multiply by 100
If you calculate:
20 ÷ 80 = 0.25
the answer is not yet written as a percentage.
Multiply by 100:
0.25 × 100 = 25%
2. Using the wrong original value
When calculating percentage increase or decrease, the original value is normally used as the reference value.
For example, if a price changes from $100 to $120, the increase is $20 and the percentage increase is:
20 ÷ 100 × 100 = 20%
3. Confusing percentage change with percentage points
Percentages and percentage points are not always the same thing.
For example, if an interest rate changes from 5% to 7%, the increase is 2 percentage points.
The relative percentage increase is:
[(7 − 5) ÷ 5] × 100 = 40%
So the rate increased by 2 percentage points, but by 40% relative to its original value.
4. Reversing the part and whole
For the question “What percentage is 20 of 80?”, use:
20 ÷ 80 × 100
not:
80 ÷ 20 × 100
The part comes first and the whole comes second.
Percentage Formula Cheat Sheet
Keep these formulas handy:
Basic Percentage
Percentage = (Part ÷ Whole) × 100
Percentage of a Number
Result = (Percentage ÷ 100) × Number
Percentage Increase
Percentage Increase = [(New − Original) ÷ Original] × 100
Percentage Decrease
Percentage Decrease = [(Original − New) ÷ Original] × 100
Percentage Change
Percentage Change = [(New − Original) ÷ Original] × 100
Frequently Asked Questions
How do you calculate a percentage?
Divide the part by the whole and multiply the result by 100.
Percentage = (Part ÷ Whole) × 100
How do you calculate 20% of a number?
Convert 20% to 0.20 and multiply it by the number.
For example:
20% of 150 = 0.20 × 150 = 30
How do you find what percentage one number is of another?
Divide the first number by the second number and multiply by 100.
For example:
30 ÷ 120 × 100 = 25%
Therefore, 30 is 25% of 120.
What is the easiest way to calculate a percentage?
For basic calculations, use the percentage formula:
(Part ÷ Whole) × 100
For more complicated calculations, an online percentage calculator can save time and reduce calculation errors.
How do you calculate percentage increase?
Subtract the original value from the new value, divide the result by the original value, and multiply by 100.
Percentage Increase = [(New − Original) ÷ Original] × 100
How do you calculate percentage decrease?
Subtract the new value from the original value, divide by the original value, and multiply by 100.
Percentage Decrease = [(Original − New) ÷ Original] × 100
Is 0.25 the same as 25%?
Yes. To convert 0.25 into a percentage, multiply it by 100:
0.25 × 100 = 25%
What does 100% mean?
100% represents the complete amount or whole. For example, if you completed all 50 tasks assigned to you, you completed 100% of the tasks.
Final Takeaway
Calculating percentages becomes straightforward once you know which formula to use. For a basic percentage, divide the part by the whole and multiply by 100. For percentage increases, decreases, and changes, compare the difference with the original value.
The key formulas are:
Percentage = (Part ÷ Whole) × 100
Percentage Increase = [(New − Original) ÷ Original] × 100
Percentage Decrease = [(Original − New) ÷ Original] × 100
For quick calculations, you can also use the CalculatorPool Percentage Calculator instead of calculating everything manually.