How much did a value increase or decrease?
Work out the percentage increase or decrease between two numbers.
change = (new − original) / original
Why is a percentage decrease shown as negative?
The sign shows direction: a negative result means the new value is lower than the original, a positive result means it grew. A -20% change and a +20% change are not opposites of the same magnitude in reverse — going up 20% then down 20% does not return you to the start.
Does the order of the two values matter?
Yes. Percentage change is always calculated relative to the original value, so swapping "original" and "new" changes the result, not just its sign.