Formula & example
Percentage change = (new value − original value) ÷ |original value| × 100. An original value of zero cannot be used as the denominator.
Example
Example: a change from 1,200 to 1,350 is (1,350 − 1,200) ÷ 1,200 × 100 = 12.5%.
People often mix up percentage change with percentage points. If an interest rate moves from 5% to 7%, that's a 2 percentage point increase, but it's a 40% percentage increase relative to the starting rate (2 ÷ 5 × 100 = 40%). News headlines sometimes blur this distinction, so it's worth checking which one is actually being reported.
Another example
A stock priced at $80 that rises to $92 gained (92 − 80) ÷ 80 × 100 = 15%.