Percent Change Calculator
The percentage increase or decrease between an original and a new value — the number behind price changes, growth reporting, and 'how much did this actually change' questions that raw differences don't answer on their own.
Inputs
Result
25%
Increase
How the percent change calculator works
Percent change = ((new value − original value) ÷ |original value|) × 100.
A positive result is an increase; a negative result is a decrease. Using the absolute value of the original keeps the sign meaningful even when the original value itself is negative.
Worked example: from 120 to 150
- Change = 150 − 120 = 30.
- Percent change = 30 ÷ 120 × 100 = 25%.
- Reversing direction, from 150 back to 120, gives (120−150)÷150×100 = −20% — proof that percent increase and the corresponding percent decrease are not the same size, since the base changed.
Common mistakes to avoid
Assuming a percent increase and decrease of the same raw amount are symmetric
A 25% increase from 120 to 150 is undone by a 20% decrease, not 25%, because the percentage base (the denominator) changes depending on which direction you're calculating from.
Using the new value as the denominator by mistake
Percent change is always measured against the original value, not the new one — dividing by the wrong number gives a plausible-looking but incorrect percentage.
Frequently asked questions
Why isn't a 25% increase undone by a 25% decrease?
Because the base for each percentage is different — 25% of 120 is 30 (getting you to 150), but 25% of 150 is 37.5, not 30, so a 25% decrease from 150 overshoots down to 112.5.
How is percent change different from percentage points?
Percent change is a relative measure (proportional to the original value); percentage points are an absolute difference between two percentages, e.g. going from 20% to 25% is a 5 percentage-point rise but a 25% relative increase.
Can percent change exceed 100%?
Yes, easily — if a value more than doubles, the percent change is over 100%. Going from 50 to 200 is a 300% increase.
What does a percent change of exactly 0 mean?
The new value is identical to the original — no change occurred.
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