This is how to calculate the date in a worksheet with the same value as strgen.You can check the date on the worksheet.

Cell H1 8 or 15

Cell H2

=TEXT(TODAY()-WEEKDAY(NOW(),1)+H1,"mm.dd.yy") & ".xlsm"

Function strgen()
    strgen = ThisWorkbook.Sheets("Sheet1").Range("H2").Value
End Function