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.

If you are unfamiliar with inputting formulas into Microsoft Excel, the much simpler way to get the number of unique values in an Excel column is through a filter.

In Excel 2003, Subtotals is on the Data menu. In the resulting dialog, choose Count from the Function dropdown. Click OK and Excel will display a subtotal for each date in the Due column.

Learn how to count the number of unique and distinct values in a column based on data in another column using array in Microsof Excel.