Excel VBA Dynamic autofill formula

sequoiacyclist 

Sorry, I wasn't clear about what the code should replace (also, i've now been able to get on a machine and test it and replaced column numbers with letters, in my code - The following replaces the whole section you have shown in your original thread.  Let me know if this works for you:

Dim Lrow As Long

Range("C3").Select
'Find last row number with value in column C
Lrow = Cells(Rows.Count, "C").End(xlUp).Row
'Select range A3 to A + Last row number previously found and enter formula
Range("A3:A" & Lrow).FormulaR1C1 = "=LEFT(RC[2], R1C9)"

Range("C3").Select
'Find last row number with value in column B
Lrow = Cells(Rows.Count, "B").End(xlUp).Row
'Select range B3 to B + Last row number previously found and enter formula
Range("B3:B" & Lrow).FormulaR1C1 = "=RIGHT(RC[1], LEN(RC[1])-R1C9-3)"
Range("A1").Select

sequoiacyclist 

Try this!

Sub test()

Dim Lrow As Integer

Range("C3").Select
Selection.End(xlDown).Select

Lrow = Selection.Row

Range("A3").FormulaR1C1 = "helloA"

Range("A3").Select
Selection.AutoFill Destination:=Range("A3:A" & Lrow), Type:=xlFillDefault

Range("B3").FormulaR1C1 = "helloB"

Range("B3").Select
Selection.AutoFill Destination:=Range("B3:B22")

End Sub

Just replace the "helloA" and "helloB" with your formulae!