By using the Highlight Cells Rules, you can highlight duplicate cells in your Excel worksheet to avoid confusion and mistakes.

Then, click the Conditional Formatting dropdown in the Styles group. From the dropdown, choose Highlight Cells Rules, and then choose Duplicate Values from the resulting submenu (Figure A).

If you wish to count the same or duplicate values in a column only once in Excel or the count of occurances of duplicate values, read this article.

Instead, select the cell containing the formula, and double-click the fill handle rather than dragging it. In an instant, Excel duplicates the formula down the column until it reaches a blank row.

If you want duplicate values to stand out in an Excel spreadsheet, you can choose between two conditional formatting rules.