How to calculate percentage change
Subtract the original value from the new value, divide by the original value, and multiply by 100.
((new value − original value) ÷ original value) × 100
Percentage increase example
From 80 to 100: ((100 − 80) ÷ 80) × 100 = 25% increase. The amount changed is 20.
Percentage decrease example
From 100 to 80: ((80 − 100) ÷ 100) × 100 = 20% decrease. The amount changed is −20.
What if the original value is zero?
Percentage change is undefined when the starting value is zero because division by zero is not possible. This calculator accepts positive original values and nonnegative new values. For changes involving negative starting or ending values, describe the absolute difference and the context instead of assuming a conventional percentage change.