How to Compare Cells in Excel

1. Open a new Excel worksheet. Enter or import the first set of data into column A.
2. Enter or import the second column of data into Column C of the same worksheet. Leave Column B empty.
3. Type this formula in cell B1: '=IF(ISERROR(MATCH(A1,$C$1:$C$#,0)),'',A1)', replacing # with the row number of the last value in column C.
4. Select cells in column B, starting at B1 and dragging your mouse down to the cell that corresponds to the last row in columns A and/or C.
5. Go to the Home tab, click on 'Fill,' then select 'Down' from the drop-down menu to finish comparing the cells. Any duplicate numbers will appear in column B between the relevant cells in columns A and C.