One common method
LastRow = Cells.SpecialCells(xlCellTypeLastCell).Row
which is not very exact, because Excel doesn’t keep track of the last cell in a very adequate form.
Another method to find the last used row in a particular column is:
LastRowColA = Range("A65536").End(xlUp).Row
but this doesn’t tell you FOR SURE the last used row in the entire sheet, unless you can be certain that Column A holds the data.
A couple extra methods are more reliable.
LastRow = Cells.Find("*",SearchOrder:=xlByRows,SearchDirection:=xlPrevious).Row
or
LastRow = ActiveSheet.UsedRange.Rows.Count
Source: http://www.mrexcel.com/td0058.html