Percentage Change Calculator
Calculate the percentage increase or decrease between an old value and a new value.
About the % Change Calculator
When you have two numbers from different points in time — last year's price versus this year's, or a before-and-after measurement — percentage change tells you how much things moved, expressed as a single signed percentage.
How It Works
The calculator subtracts the old value from the new value to find the raw change, then divides that by the absolute value of the old value and multiplies by 100. A positive result is reported as a percentage increase, and a negative result as a percentage decrease.
Percentage Change (%) = (New Value − Old Value) / |Old Value| × 100.
Worked example
Scenario: A value that moves from 50 to 65.
- Raw change: 65 − 50 = 15.
- Percentage change: 15 ÷ 50 × 100 = 30%.
- Because the change is positive, it is shown as a 30% increase.
Result: A 30% increase.
Percentage change vs. percentage difference
Use percentage change when one value is clearly the starting point and the other is the later value. The old value is the baseline, so the result has direction: positive for an increase and negative for a decrease. For two values with no natural “before” and “after,” use percentage difference instead.
Tips and common mistakes
- Percentage change depends on direction: 50 → 65 is +30%, but 65 → 50 is −23.08%.
- If the old value is zero, percentage change is undefined — report the raw change instead.
- For comparing two values with no 'before' and 'after', use Percentage Difference.
Assumptions & Limitations
- Uses the absolute value of the old value in the denominator so the sign of the result always correctly reflects an increase or decrease, even if the old value itself was negative.
- If the old value is zero, percentage change is mathematically undefined since you cannot divide by zero — use the raw difference instead in that case.