How to Calculate Percentage: Percentage Formula, Increase, Decrease & Examples

Percentages are everywhere. You use them when calculating discounts, exam scores, salary increases, business growth, taxes, tips, profits, price changes, and many other everyday calculations.

But percentage questions can become confusing when you need to work out an increase, decrease, difference, or the original value before a percentage was applied.

The good news is that most percentage problems can be solved using a few simple formulas.

In this guide, you'll learn how to calculate percentages, understand the most important percentage formulas, see practical examples, and learn when to use each type of calculation.

For a quick answer, you can also use our Percentage Calculator to calculate percentages instantly.

What Is a Percentage?

A percentage is a number expressed as a fraction of 100.

The word "percent" literally means "per hundred."

For example:

10% means 10 out of 100
25% means 25 out of 100
50% means 50 out of 100
75% means 75 out of 100
100% means the entire amount

A percentage can also be written as a decimal:

10% = 0.10
25% = 0.25
50% = 0.50
75% = 0.75
100% = 1.00

To convert a percentage into a decimal, divide it by 100.

The Basic Percentage Formula

The basic percentage formula is:

Percentage = (Part ÷ Whole) × 100

For example, suppose you scored 45 marks out of 60.

Your percentage is:

(45 ÷ 60) × 100 = 75%

So, 45 out of 60 is 75%.

If you want to calculate a percentage without doing the calculation manually, use our Percentage Calculator.

How to Calculate a Percentage of a Number

One of the most common percentage questions is:

What is X% of Y?

Use this formula:

Result = (Percentage ÷ 100) × Number

Example: What is 20% of 150?

Convert 20% into a decimal:

20 ÷ 100 = 0.20

Then multiply:

0.20 × 150 = 30

Therefore:

20% of 150 = 30

Another example

What is 15% of 240?

15 ÷ 100 = 0.15

0.15 × 240 = 36

Therefore:

15% of 240 = 36

For fast calculations, use our Percent of a Number Calculator.

How to Calculate What Percentage One Number Is of Another

Sometimes you know the part and the total, but you want to know the percentage.

Use:

Percentage = (Part ÷ Whole) × 100

Example

30 is what percentage of 120?

30 ÷ 120 = 0.25

0.25 × 100 = 25%

Therefore:

30 is 25% of 120.

This calculation is useful for exam scores, business metrics, sales performance, survey results, and many everyday situations.

How to Calculate Percentage Increase

A percentage increase tells you how much a number has increased compared with its original value.

The formula is:

Percentage Increase = ((New Value − Original Value) ÷ Original Value) × 100

Example: Price Increase

Suppose a product originally costs $80 and now costs $100.

First find the difference:

$100 − $80 = $20

Then divide by the original value:

$20 ÷ $80 = 0.25

Multiply by 100:

0.25 × 100 = 25%

Therefore:

The price increased by 25%.

The original value is always the reference point when calculating percentage increase.

Use our Percentage Increase Calculator to calculate this automatically.

How to Calculate Percentage Decrease

Percentage decrease is used when a value becomes smaller.

The formula is:

Percentage Decrease = ((Original Value − New Value) ÷ Original Value) × 100

Example: Price Decrease

A product originally costs $100 but is now $75.

Difference:

$100 − $75 = $25

Divide by the original value:

$25 ÷ $100 = 0.25

Multiply by 100:

0.25 × 100 = 25%

Therefore:

The price decreased by 25%.

This calculation is particularly useful for discounts, price reductions, depreciation, sales declines, and other situations where a value decreases.

How to Calculate Percentage Change

Percentage change is used to compare an original value with a new value.

The formula is:

Percentage Change = ((New Value − Original Value) ÷ Original Value) × 100

For example, if revenue increases from $50,000 to $60,000:

Difference:

$60,000 − $50,000 = $10,000

Percentage change:

($10,000 ÷ $50,000) × 100 = 20%

Therefore:

Revenue increased by 20%.

If the new value is smaller than the original value, the result represents a percentage decrease.

Percentage Increase vs. Percentage Difference

These terms are often confused.

Percentage increase

Percentage increase uses a specific starting value as the reference.

For example:

$100 → $120

The increase is:

($120 − $100) ÷ $100 × 100 = 20%

Percentage difference

Percentage difference is generally used when comparing two values without treating either value as the starting point.

The formula is:

Percentage Difference = |A − B| ÷ ((A + B) ÷ 2) × 100

For example, compare 80 and 100:

Difference = 20

Average = 90

Percentage difference:

20 ÷ 90 × 100 ≈ 22.22%

This distinction matters when deciding which calculator to use.

How to Add a Percentage to a Number

Suppose you want to increase 500 by 20%.

First calculate 20%:

500 × 0.20 = 100

Then add it to the original:

500 + 100 = 600

So:

500 increased by 20% = 600

There is also a shortcut:

500 × 1.20 = 600

To increase a number by a percentage, multiply it by:

1 + percentage ÷ 100

How to Subtract a Percentage from a Number

Suppose you want to decrease 500 by 20%.

Calculate the percentage:

500 × 0.20 = 100

Subtract it:

500 − 100 = 400

Therefore:

500 decreased by 20% = 400

Shortcut:

500 × 0.80 = 400

To decrease a number by a percentage, multiply it by:

1 − percentage ÷ 100

How to Calculate a Discount Percentage

Percentage calculations are commonly used when shopping.

Suppose an item costs $200 and has a 25% discount.

Discount amount:

200 × 25 ÷ 100 = $50

Sale price:

$200 − $50 = $150

Therefore:

25% off $200 = $150

You can use our Percentage Discount Calculator to calculate the discount amount and final price.

How to Calculate Percentage of Marks

Percentage is commonly used to calculate exam results.

The formula is:

Marks Percentage = (Obtained Marks ÷ Total Marks) × 100

For example, if you scored 425 marks out of 500:

425 ÷ 500 × 100 = 85%

Therefore:

425 out of 500 = 85%

The same formula works for tests, assignments, exams, and other scoring systems.

How to Calculate Salary Percentage Increase

Percentage calculations are also useful when comparing salaries.

Suppose your salary increases from $2,000 to $2,300.

Difference:

$2,300 − $2,000 = $300

Percentage increase:

$300 ÷ $2,000 × 100 = 15%

Therefore:

The salary increased by 15%.

You can use a Salary Increase Calculator when comparing your old and new salary.

How to Find the Original Value After a Percentage Increase

Sometimes you know the final value and the percentage increase, but you need to find the original amount.

For an increase:

Original Value = Final Value ÷ (1 + Percentage ÷ 100)

Example

A product costs $120 after a 20% increase. What was the original price?

120 ÷ 1.20 = 100

Therefore:

The original price was $100.

This is known as a reverse percentage calculation.

How to Find the Original Price After a Discount

Suppose an item costs $80 after a 20% discount.

The original price is:

Original Price = Final Price ÷ (1 − Discount ÷ 100)

So:

80 ÷ 0.80 = 100

Therefore:

The original price was $100.

This is especially useful when you know the sale price but want to find the original price.

Why a 50% Increase and 50% Decrease Are Not the Same

This is one of the most common percentage mistakes.

Start with 100.

Increase it by 50%:

100 × 1.50 = 150

Now decrease 150 by 50%:

150 × 0.50 = 75

You end up with:

75, not 100.

Why?

Because the second 50% is calculated from 150, not from the original 100.

The percentage's reference value matters.

Common Percentage Mistakes
1. Dividing by the wrong number

When calculating percentage increase, divide the difference by the original value, not the new value.

1. Forgetting to multiply by 100

A decimal such as 0.25 represents 25%.

1. Confusing percentage points with percentage change

A change from 20% to 25% is:

5 percentage points

But the relative percentage increase is:

25%

These are different measurements.

1. Assuming equal increases and decreases cancel out

A 20% increase followed by a 20% decrease does not return exactly to the original value.

1. Using the wrong baseline

Always identify the value that should be used as the reference before calculating percentage change.

Quick Percentage Reference
Calculation Formula
Percentage of a number (Percentage ÷ 100) × Number
What percent is X of Y? (X ÷ Y) × 100
Percentage increase ((New − Original) ÷ Original) × 100
Percentage decrease ((Original − New) ÷ Original) × 100
Percentage change ((New − Original) ÷ Original) × 100
Percentage difference
A − B ÷ ((A + B) ÷ 2) × 100
Increase a number Original × (1 + Percentage ÷ 100)
Decrease a number Original × (1 − Percentage ÷ 100)
Frequently Asked Questions
What is the easiest way to calculate a percentage?

The easiest way is to use a percentage calculator. For manual calculations, identify the part and whole, divide the part by the whole, and multiply by 100.

What is the formula for percentage?

The basic formula is:

Percentage = (Part ÷ Whole) × 100

How do I calculate 10% of a number?

Divide the number by 10.

For example:

10% of 300 = 30.

How do I calculate 20% of a number?

Multiply the number by 0.20.

For example:

20% of 250 = 50.

How do I calculate percentage increase?

Use:

((New Value − Original Value) ÷ Original Value) × 100

How do I calculate percentage decrease?

Use:

((Original Value − New Value) ÷ Original Value) × 100

What is the difference between percentage change and percentage difference?

Percentage change uses a defined original value as the baseline. Percentage difference compares two values using their average as the reference.

Can I calculate percentages with decimals?

Yes. Percentage calculations work with whole numbers, decimals, fractions, and many other numerical values.

Calculate Any Percentage Instantly

Whether you need to calculate a percentage of a number, find percentage increase or decrease, compare two values, calculate a discount, or work backward to find an original value, a calculator can save time and reduce calculation errors.

Use our Percentage Calculator to get your result instantly and see the calculation clearly.

For more specific calculations, explore our percentage-related calculators and guides throughout PercentagCalculator.com.