I use the following:
lastrow = ActiveSheet.Columns("A").Cells.Find("*", SearchOrder:=xlByRows, LookIn:=xlValues, SearchDirection:=xlPrevious).Row
It'll find the last row in a specific column. If you want the last used row for any column then:
lastrow = ActiveSheet.Cells.Find("*", SearchOrder:=xlByRows, LookIn:=xlValues, SearchDirection:=xlPrevious).Row