Sum depending of headers of rows/columns + column before

[Jeanb25]

Hello,

I've got a table like that :

I'd like to fill this table, the column "nb of days" for each months with :
- the forecast column of the current month + the "adjustment" column of previous month that sum for a specific level (if 2 people have the same level they are sum up)

Currently I'm able to do it with the forecast column of the current month only.
The formula I use is :

SUMPRODUCT(('TimeSheet'!$A$3:$A$7='Facturation'!$A3)*('TimeSheet'!$C$1:$T$1='Facturation'!B$1);'TimeSheet'!$C$3:$T$7)

Any idea on how I can do it ? I tried to play with offset but no luck to do it :'(

 

[Jeanb25]

I tried to do an array in some cells below, then an offset array of those cells then the sumproduct, but i think it may have something better as I have my sheet filled with 0 and 1 everywhere now :D.

Any one have a solution ? :/

 

[Jeanb25]

I think it's undoable :D