If the value does appear more than once, we run another IF + COUNTIF combo.
So, at each row, the formula checks the count inside the range up to the current row.
Each additional column also needs to be entered as an expanding range.
Flag first duplicate in a list
To mark the first duplicate in a list, you can use a formula based on the COUNTIF function. Optionally, you can flag subsequent duplicates with a different marker. In the example shown the formula in cell C4 is: =IF(COUNTIF($B$4:$B$11,B4)>1,IF(COUNTIF($B$4:B4,B4)=1,"x","xx"),"") This formula has been copied down the column, from C4 to C11.
