Analysing change in gross profit margin % by change in revenue mix % and contribution margin %

[clintazz]

Hi all,
I am trying to explain the difference in the forecast and actual gross margin % by analysing the difference between a) change in the revenue mix b) change in in the % margin of the various products sold.
My question is, should I apply the following logic
(Change in revenue mix % of product Z * Forecast Margin % of product Z ) + (Change in margin % of product Z * Actual revenue mix % of product Z)
OR
(Change in revenue mix % of product Z * Actual Margin % of product Z ) + (Change in margin % of product Z * Forecast revenue mix % of product Z)
I am dealing with a multi-product scenario so I will be calculating the above for all the products.
I greatly appreciate your help on this
Clint

 

[Flashback]

Why you added ACT to FCT figures? Should be subtracted and compare variances on YTD basis. The order is not important, but should be the same formula in all positions.