While googling for percent difference formulas, I got two different formulas:
- (difference/old-value)$\times 100$.
- (difference/average)$\times 100$.
So, for $6$ and $9$, the first one gives $-33$ and the second gives $-40$. Which one is correct and when is either formula used?
It depends on what you are trying to do.
If you start out with $6$ and then it increases to $9$, and you want to know by how much the original value increased (or decreased), then you use **[(new value - old value)/old value] * 100. So, here, it would be $\dfrac{9 - 6}{6}*100 = \dfrac{3}{6}*100 = 50$%. (If when using this formula, your percent is a negative number, then that is the percentage it decreased by.