How to Calculate Percentage Change

Direct Answer

Percentage change shows how much a value moved compared with the original value. Use this formula: (new value - old value) / old value x 100. A positive result is an increase, and a negative result is a decrease.

Old value: 120
New value: 150
Change: 150 - 120 = 30
30 / 120 = 0.25
0.25 x 100 = 25% increase

Step-by-Step Method

Write the old value and new value before doing the math. Most mistakes happen because the baseline is swapped or because the percent sign is added before multiplying by 100.

• Subtract the old value from the new value
• Divide the change by the old value
• Multiply the result by 100
• Label the result as an increase or decrease
• Round only after the final step if you need a clean display

Decrease Example

The same formula works when the new value is smaller. The result is negative because the value went down.

Old value: 80
New value: 60
Change: 60 - 80 = -20
-20 / 80 = -0.25
-0.25 x 100 = -25%, so this is a 25% decrease

When to Use It

Use percentage change when the starting value matters. It is useful for comparing growth, reductions, quantities, scores, traffic, prices, or repeated measurements as long as the old value is a meaningful baseline.

• Use old value as the baseline when comparing before and after
• Use percentage points when comparing two percentages directly
• Use the raw difference when the original value is zero or not meaningful
• Name the time period or source so the comparison is traceable

Limits and Common Mistakes

A standard percentage change is not defined when the old value is zero because the formula divides by zero. If a count moves from 0 to 12, say it increased by 12 items or changed from none to 12 instead of claiming an infinite percent increase.

• Do not swap the old and new values unless you mean to change the baseline
• Do not confuse a 5 percentage point move with a 5 percent change
• Do not round early when the number will be used in another calculation
• Be careful with negative baselines because the wording can become confusing

Common Percentage Point Confusion

Moving from 10% to 15% is a 5 percentage point move, but it is a 50% relative increase from the original 10%. Use percentage change for the relative movement and percentage points for the simple difference between two percent values.

Old rate: 10%
New rate: 15%
Percentage point change: 15 - 10 = 5 points
Percentage change: 5 / 10 x 100 = 50%