Iferror(sumproduct) to sort by due date

I think you are close to the correct formula there, but first, let me introduce you to Excel Tables: http://www.utteraccess.com/wiki/Tables_in_Excel. There are a lot of advantages to tables in Excel. The two that really count here are:

1. Tables know how big they are, so you don't have to guess how big your formulas have to be. I notice that you reference about 4600 rows even though you barely have a quarter of that. By referencing the table, the table will reference the 1083 rows you have. When you add row 1084, the table will grow to accommodate it.

2. You can use the table header names in formulas. You don't have to remember that column K is Code and Column F is Date Closed.

Tables also copy down formulas, formats, validations ... automatically, and they are just as easy to reference in VB.

So your new formula looks like:=IFERROR(SUMPRODUCT(--(Table1[Code]="P/S"),--(MONTH(Table1[Date Closed])>=1),Table1[Workdays in queue])/SUMPRODUCT(--(Table1[Code]="P/S"),--(MONTH(Table1[Date Closed])>=1),--(Table1[Date Closed]<>"")),0)

All I did was throw in one more condition: --(Table1[Date Closed]<>"")

And if you change the name of the table from Table1, the formulas will catch it.