speed up formulas

Edit: see my last post on this thread.


I've got large workbook (about 200,000 cells) which uses Solver. After reading of ways to increase the speed of Excel, one source suggests that I replace SUMIFS formulas with VLOOKUP and INDEX-MATCH. It also says that OFFSET slows down computing time but does not suggest an alternative.

Here are two of my current formulas which use the "slow" method. Can anyone suggest a reformulation of these? If you'd like I can upload a sample of the workbook.

=SUMIFS(O$122:O$2064,A$122:A$2064,">="&EOMONTH(L6,-1)+1,A$122:A$2064,"<="&EOMONTH(L6,0))

=IF(FP4=FP3+1,INDEX($FN$4:$FN$1834,MATCH(FP4,$FM$4:$FM$1834,0)),AVERAGE(OFFSET($FN$4,MATCH(FP3,$FM$4:$FM$1834,0),,FP4-FP3,1)))

Thanks!