How to Calculate Percentage Increase and Decrease

Overview

Percentage change measures how much a value has risen or fallen relative to its original value.

Objective

Calculate the percentage increase or decrease between an original value and a new value.

What You Need

• Original value
• New value
• Calculator or paper

Before You Start

Find the difference between the new and original values, then compare that difference with the original value.

How to Calculate

1. Find the change: new value − original value.
2. For a decrease, use the size of the decrease as a positive change amount.
3. Divide the change by the original value.
4. Multiply by 100 to convert to a percentage.
5. Label the result as an increase or decrease.

Worked Example

A price rises from $80 to $100. The increase is $20. 20 ÷ 80 × 100 = 25%, so the price increased by 25%.

Useful Tips

• Always divide by the original value, not the new value.
• Calculate the dollar or unit change first.
• A quick estimate can help confirm the result.

Common Mistakes

• Dividing by the new value.
• Using the difference without converting it to a percentage.
• Confusing percentage change with percentage points.

Important Notes

Successive percentage changes do not simply cancel. A 20% rise followed by a 20% fall does not return to the starting value because the second change uses a different base.

FAQ

What is the basic formula?

Percentage change = change ÷ original value × 100.

Why don’t equal percentage increases and decreases cancel?

Because each percentage is applied to a different starting amount.