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 page.In Excel 2010, the PERCENTILE function has been renamed the PERCENTILE.INC function.
Although it has been replaced, the Percentile function is still available in current versions of Excel (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 syntax of the function is:
Where the function arguments are:
array    The array 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 A1A6 of the sample spreadsheet, for different values of k.
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 either:

#VALUE!    Occurs if the supplied value of k is nonnumeric. 