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

Percentages are one of the most common types of calculations people use every day. From calculating discounts and exam scores to comparing prices, salary increases, business growth, and changes in expenses, understanding percentages is an essential math skill.

The good news is that most percentage calculations use a few simple formulas.

If you want to skip the manual calculation, you can use the Percentage Calculator to calculate percentages, percentage increases, decreases, and changes instantly.

What Is a Percentage?

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

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% represents the whole amount

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

How to Calculate a Percentage

The basic percentage formula is:

Percentage = (Part ÷ Whole) × 100

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

45 ÷ 60 × 100 = 75%

Therefore, your score is 75%.

How to Calculate a Percentage of a Number

Another common question is:

What is 20% of 150?

Convert 20% to a decimal:

20 ÷ 100 = 0.20

Then multiply:

0.20 × 150 = 30

So, 20% of 150 is 30.

This type of calculation is useful when working out discounts, taxes, tips, commissions, and other amounts.

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

For example, if a product increases from $80 to $100:

100 − 80 = 20

20 ÷ 80 × 100 = 25%

The price increased by 25%.

How to Calculate Percentage Decrease

Percentage decrease works similarly.

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

Suppose a product falls from $100 to $75:

100 − 75 = 25

25 ÷ 100 × 100 = 25%

The price decreased by 25%.

Percentage Change vs Percentage of a Number

These calculations are related but answer different questions.

If you ask "What is 20% of 500?", you are finding a portion of a number.

If you ask "What percentage did the price change from 500 to 600?", you are measuring the change relative to the original value.

Always identify what the question is asking before choosing a formula.

Common Percentage Mistakes

One of the most common mistakes is using the new value instead of the original value when calculating percentage change.

For percentage change, the original value is normally the reference point.

Another mistake is confusing percentage points with percentage change. For example, an interest rate moving from 5% to 7% is a 2-percentage-point increase, not simply a 2% increase.

Calculate Percentages Instantly

You don't have to work through every percentage problem manually.

Use the MyDailyCalculator Percentage Calculator to calculate percentages, increases, decreases, and changes quickly.

Whether you're checking a discount, comparing prices, calculating a score, or analyzing business numbers, a percentage calculator can help you verify the result.

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