@ALLOCATE and its infamous cousin @MDALLOCATE works, but I find it works quite slowly, and prefer to write my own allocation logic. So in your simple case, I would use something like the following in a calc script:
"Accnt_1"("Accnt_1"->"YearTotal" / 12);
So no need for 12 lines, one per month. If you start making clever use of @PARENTVAL and @ANCESTVAL you can get quite creative with your allocations.
However for very complex allocations @ALLOCATE and @MDALLOCATE does offer some neat tricks to do a lot in a single line of code, just be wary of the performance.