How to calculate percentage change, up or down

Steps

1. Write down the old value and the new value. Here: 80 and 100.
2. Subtract the old from the new: 100 − 80 = 20.
3. Divide that difference by the old value: 20 ÷ 80 = 0.25.
4. Multiply by 100 to get the percentage: 25%.
5. A positive result is an increase and a negative result is a decrease. Or enter both numbers in the percentage change calculator.

Always divide by the old value

The percentage is measured against where you started, so the old value goes underneath. Going from 50 to 75 is an increase of 25, which is 50% of 50. Going from 200 to 150 is a decrease of 50, which is 25% of 200.

Using the new value instead is the most common mistake, and it gives a wrong answer every time the two numbers differ.

Why the way back is a different percentage

From 80 to 100 is up 25%. From 100 back to 80 is down 20%. The gap is the same 20, but it is measured against 80 in one case and 100 in the other. This is also why a 50% rise followed by a 50% fall does not bring you back to the start: 100 becomes 150, and 150 becomes 75.

Percentage change or percentage points

If a rate rises from 10% to 12%, it has gone up 2 percentage points, but by 20% as a percentage change of the rate itself. Reports mix the two, so check which one is meant. Use percentage change for prices, salaries, sales and any other quantity, and percentage points for changes in a rate.