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I want to calculate 25% growth over prior year's sale (by month). The way I am solving this currently is by multiplying (sale)*1.25; this works fine for sale values that are positive but for those that are negative I get that the 25% growth is more negative than the the sale amount. I don't want to tell the salesperson that I want them to sale even less than they have sold in the prior year.

Example:

Prior Year Jan - 40000 Feb - -20000 (negative because they can have sales taken away)

Current Year - I want the salesperson to have a growth of 25% over their prior year amount Jan - 40000*1.25 = 50000 Feb - -20000*1.25=-25000 (based on my calculation they should actually be at -15000, this is 25% growth from their -20000)

I am trying to find a solution that works for both scenario as it needs to go into a equation/formula.

Thank you very much for your help!

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  • $\begingroup$ My wife (who has been a sales manager) says you should tell any salesperson who is generating negative sales they're getting the Glengarry Glen Ross third prize. $\endgroup$ – Barry Cipra Jun 16 '15 at 20:42
  • $\begingroup$ heheh. We joke that we should tell them to do a better job :P $\endgroup$ – Mary Jun 17 '15 at 14:46
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The problem is, that you have negative sales (whyever). Your data don´t have a zero point. Thus they are not ratio scaled. But this is the assumption to calculate a growth rate for every month.

I don´t really understand, why you have negative sales. This doesn´t sounds logical to me.

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  • $\begingroup$ That is the issue we are running into as well. We have negative sales because sometimes sales can be taken away/backdated. This causes months where a salesperson already has low sales to fall into a negative if a reversal has taken place. $\endgroup$ – Mary Jun 17 '15 at 14:26
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    $\begingroup$ @Mary You should apportion the reversal to the period, when the sales happened. Then you wouldn´t get negative sales. This would be also the correct calculation within the meaning of accounting. $\endgroup$ – callculus Jun 17 '15 at 15:07
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Mathematically speaking, a 25% growth will always be found by multiplying by 1.25. It looks like you're looking for a 25% improvement, so to speak, over the previous values. For what you want to do, a formula like $f(n) = n + 0.25|n|$ will suffice.

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