Quick answer: Percentage increase measures how large an upward change is relative to the original value. The starting value—not the final value—is the denominator.
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Percentage change formula
Percentage change = (new value − original value) ÷ original value × 100.
Start with a value of 80 and end at 100. The difference is 20, and 20 ÷ 80 × 100 = 25%. Because the difference is positive, this is a 25% increase.
For a decrease, the same formula returns a negative result. For example, $250 becomes $200: (200 − 250)/250 × 100 = −20%, meaning a 20% decrease.
Worked examples
| Original | New | Change | Percentage change |
|---|---|---|---|
| 80 | 100 | +20 | +25% |
| 250 | 200 | −50 | −20% |
| 40 | 50 | +10 | +25% |
| 120 | 120 | 0 | 0% |
Always compare the difference against the original value, not the new one.
Percentage points are different
If a rate rises from 20% to 25%, the increase is 5 percentage points. Relative to the original 20%, the increase is 25%. When the input is already a percentage, specifying which kind of change you mean avoids confusion.
Consecutive increases and decreases
A 20% increase from 100 produces 120. A subsequent 20% decrease applies to 120 and produces 96. The overall change is −4%, not zero. Multiply the factors: 1.20 × 0.80 = 0.96.
Excel and Google Sheets
If A2 is the original number and B2 is the new number, use =IF(A2=0,"N/A",(B2-A2)/A2) and format the result as a percentage. A zero original value makes this standard formula undefined. If you need to describe a zero-to-positive change, report the absolute change instead.
Important edge cases
A negative starting number may produce a mathematically valid calculation but an unintuitive real-world interpretation. State the original value and the context, rather than relying on a percentage label alone. Round only at the end when possible.
Pick a meaningful baseline
A percentage change is only interpretable when the starting value represents a sensible comparison. If sales rise from 10 to 15 units, the change is 50%. If they rise from 1,000 to 1,005 units, the absolute increase is the same five units but the relative change is only 0.5%. Neither number is inherently more important: each answers a different question.
For small baselines, percentages can look dramatic. Show the original and new values alongside the percentage so readers can judge the size of the underlying change.
Check with a multiplier
An increase of 25% corresponds to multiplying the original positive quantity by 1.25. If an 80-unit starting point becomes 100, dividing 100 by 80 gives 1.25 and confirms the increase. A decrease of 20% uses a multiplier of 0.80. These quick checks are useful when building spreadsheet models or reading reports.
More reading
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