The k'th percentile of a range of data is the value that k% of the data values fall within.
This is explained in more detail on the Wikipedia Percentile pageIn Excel 2010, the PERCENTILE function has been renamed the PERCENTILE.INC function.
Although it has been replaced, the Percentile function is still available in Excel 2010 (stored in the list of compatibility functions), to allow compatibility with earlier versions of Excel.
The Excel PERCENTILE function returns the k'th percentile of a supplied range of values for a given value of k.
The format of the function is :
Where the function arguments are:
array    The range of data values for which you want to calculate the k'th percentile 
k    The value (between 0 and 1) of the required percentile 
The spreadsheets below show examples of the Excel Percentile function used to calculate the k'th percentile of a set of values in cells A1  A6 of the sample spreadsheet, for different values of k.
The formulas for the functions are shown in the spreadsheet on the left, and the results are shown in the spreadsheet on the right.
Formulas:

Results:

Note that in the above examples:
For further examples of the Excel Percentile function, see the Microsoft Office website
If you get an error from the Excel Percentile function this is likely to be one of the following:
#NUM!    Occurs if the supplied value of k is less than 0 or greater than 1 
#VALUE!    Occurs if the supplied value of k is nonnumeric 