How to Calculate Percentage Increase (and Decrease)

Percentage increase and decrease are essential for understanding growth rates, price changes, salary raises, and more. This guide shows the exact formulas and worked examples.

The Percentage Increase Formula

Percentage Increase = ((New Value - Old Value) / Old Value) × 100

Example: A product costs $80, now costs $100.

((100 - 80) / 80) × 100 = (20 / 80) × 100 = 25%

The price increased by 25%.

The Percentage Decrease Formula

Percentage Decrease = ((Old Value - New Value) / Old Value) × 100

Example: A salary was $60,000, reduced to $54,000.

((60,000 - 54,000) / 60,000) × 100 = (6,000 / 60,000) × 100 = 10%

The salary decreased by 10%.

Percentage Change (General Formula)

Both formulas combine into one:

Percentage Change = ((New - Old) / Old) × 100

A positive result means increase; negative means decrease.

Common Examples

| Scenario | Old | New | Change | |----------|-----|-----|--------| | Price rise | $50 | $65 | +30% | | Stock drop | $200 | $150 | -25% | | Population growth | 10,000 | 12,500 | +25% | | Weight loss | 90 kg | 81 kg | -10% |

Finding the New Value After a Percentage Change

To find what a value becomes after a percentage increase:

New Value = Old Value × (1 + percentage/100)

Example: $1,200 after a 15% increase:

1,200 × (1 + 15/100) = 1,200 × 1.15 = $1,380

For a decrease, subtract instead:

New Value = Old Value × (1 - percentage/100)

Example: $1,200 after a 15% decrease:

1,200 × (1 - 0.15) = 1,200 × 0.85 = $1,020

Working Backwards: Finding the Original Value

If you know the new value and the percentage change, find the original:

Original = New Value / (1 + percentage/100)

Example: A price is now $115 after a 15% increase. What was the original?

115 / 1.15 = $100

Percentage Points vs. Percentage Change

These are easily confused.

• Interest rates rise from 2% to 5% — that's an increase of 3 percentage points, but a 150% increase in the rate itself.
• "Up 3 percentage points" and "up 150%" describe the same change from different perspectives.

Always clarify which one you mean when discussing rates.

Quick Mental Shortcuts

• 10% of any number: move the decimal one place left. 10% of 340 = 34
• 5%: find 10%, then halve it. 5% of 340 = 17
• 25%: divide by 4. 25% of 340 = 85
• 1%: move decimal two places left. 1% of 340 = 3.4

Use our Percentage Calculator to calculate any percentage increase, decrease, or change instantly.