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How to Calculate the Percentage Increase of a Negative Number

Updated April 17, 2017

Just as you can calculate the percentage increase between two positive numbers, you can do the same for negative numbers. However, for real life applications, the result may be meaningless or misleading. For example, to say that a company with a £9,750 loss one month underwent a 20% increase to a £11,700 loss the next month is deceptive, as the word "increase" has positive associations and implies that things got better, when in reality they got worse.

Identify which number from your problem is a and which one is b in the formula (ba)/a * 100. The first number, or pre-increase number, is a, and the second number, post-increase, is b.

Example:

What is the percentage increase from -20 to -25?

-20 = a

-25 = b

Plug in the numbers from the problem into the equation.

Example:

(ba)/a * 100

(25-20)/20 * 100

Carry out the calculations.

Example:

(25-20)/20 * 100

\= 5/20 * 100

\= 0.25 * 100

\= 25

There is a 25% increase from -20 to -25.

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About the Author

Based in Tucson, Ariz., Elio Lewis has served as a writing tutor since 2005. He received a B.A. in linguistics from the University of Arizona.