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Percentage change formula
Percentage change = (new value − old value) ÷ old value × 100. Going from 50 to 65 is (65 − 50) ÷ 50 × 100 = 30% increase.
A decrease from 65 back to 50 is only about 23.08%, because the base is different.
Frequently asked questions
Why is a 30% increase not reversed by a 30% decrease?
The second percentage is applied to a larger number.
What if the old value is 0?
Percentage change is undefined, because you cannot divide by zero.
How do I get percentage difference instead?
Percentage difference compares two values without a clear start and uses their average as the base.