Percentage Decrease Calculator

How it is calculated

The tool measures the drop from an old value to a new value as a share of the old one: decrease % = (old − new) ÷ |old| × 100. It also shows the plain difference old − new and the multiple new ÷ old, so 0.75x means the new value is three quarters of the old. The old value is the starting point, so it must not be zero, as nothing can be measured against zero. If the new value is higher than the old one, the answer is negative, meaning an increase, with no error message. Any units work as long as both values share one. The base is always the old value. Going down 25% and then up 25% does not return you to the start.

Common mistakes

• Dividing by the new value instead of the old. A drop from 80 to 60 is 25% of 80, not 33% of 60.
• Swapping the two fields. The result changes sign and reads as an increase.
• Assuming a 25% fall is undone by a 25% rise. After falling to 60, a rise back to 80 needs 33.33%, because the base is now smaller.
• Using the tool for a value that started at zero. There is no percentage decrease from zero, and the tool returns nothing.
• Applying it to negative numbers without thinking. The tool divides by the absolute old value, so the sign of a decrease can be counter-intuitive and the multiple is plain new ÷ old.