How to calculate the percentage of increase/decrease with negative numbers?

Perhaps this "formula" will be easier to understand (this formula is equivalent to your formula - each can be derived from the other):

$$\dfrac{\text{original value} \;- \;\text{final value}}{\text{original value}} \times 100\% = \text{percent change}$$

That change will be

Original value $6.11$, final value $-3.73$:

$$\dfrac{6.11 -(-3.73)}{6.11}\times 100\% \approx 161\% \;\;\text{DECREASE}$$

Original value $-2.1$, final value $0.6$:

$$\dfrac{-2.1 - 0.6}{-2.1}\times 100\% \approx 128.6\% \;\;\text{INCREASE}$$

I know this is a very old thread, but I am here for the first time so I hope it is OK to comment.

Let's take an example:

Original value $-10$, final value $10$:

$\frac{Original\ value - Final\ value}{Original\ value} = 200\% \ increase $

Original value $-1$, final value $10$:

$\frac{Original\ value - Final\ value}{Original\ value} = 1100\% \ increase $

How can an increase from a smaller number ($-10$) to $10$ be a lesser percentage than an increase from a larger number ($-1$) to $10$?

I’m not a mathematician, but I don’t think percent change with values of opposite signs is defined.

See also: http://online.wsj.com/public/resources/documents/doe-help.htm

(the section named Net Income)

Related