Working with a variable Range

[BushyIII]

My MACRO is used daily to copy data from several sheets resulting in a new sheet with a differing number of rows with every run. My problem is that I need to define this range of rows in order to do an AUTOFILL function.

I know I can use a cell to hold the row count using COUNTA. However, I cannot figure out how to then use the result of this in the range statement.
example using COUNTA within cell D100 produces a row count of 95

My MACRO needs to do the following:
A1 =Month(C1)
B1 =Year(C1)
Range("A1:B1").Select
Selection.AutoFill Destination:=Range("A2:B????"),

Thanks in advance

 

[BushyIII]

I appreciate all the help. I'll give both suggestions a try. The immediate challenge is understanding how they both work to ensure I integrate the code successfully.

Thanks again.

 

[mikerickson]

They both use .End to answer to your original question about a variable range.

 

[mikerickson]

In the PM to me, you asked "Where is the fill down?"
Rather than using the .FillDown method,

With Range(.Cells(1,1), .Cells(.Rows.Count,1).End(xlup))
     .Offset(0,-3).Value = Month(oneSheet.Cells(1,3).Value)
     .Offset(0,-2).Value = Year(oneSheet.Cells(1,3).Value)
End With

puts the values directly into the cells
One difference between my and VoG's code is what is in the cells.
In the OP, the code put numbers in A1 and B1 and used .FillDown to put those same numbers in each row. The value in A3 =Month(C1).
My code does the same, but VoG's code does the equivilant of putting the formula =MONTH(RC3) in each row, so the value in A3 = Month(C3).