In Excel 2010, the new PERCENTRANK.INC and PERCENTRANK.EXC functions both calculate the relative position of a specified value, within a supplied array of values, and return this value, as a percentage.
The difference between these two functions is that the Percentrank.Inc function calculates a value in the range 0 to 1 inclusive, whereas the Percentrank.Exc function calculates a value in the range 0 to 1 exclusive.
The Excel PERCENTRANK.INC function calculates the relative position, between 0 and 1 (inclusive), of a specified value within a supplied array.
The function is new in Excel 2010 and so is not available in earlier versions of Excel. However, Percentrank.Inc is simply a renamed version of the old Percentrank function, that is available in earlier versions of Excel.
The format of the function is :
Where the function arguments are:
array    The array of values, within which you want to find the relative position of a specific value 
x   
The specific value that you want to calculate the relative position of (x must be within the range of the values in the supplied array, but it does not need to be exactly equal to one of the values  if x is not found in the array, the array values are interpolated to calculate the percentage rank) 
[significance]   
An optional argument that specifies the number of significant digits that the returned percentage value is rounded to (By default the returned percentage value is accurate to 3 significant digits) 
Cells B1B4 of the spreadsheet below show examples of the Excel Percentrank.Inc Function used to calculate the relative position of a specific value, within the array of values in cells A1A9.
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 example in cell B2 of the spreadsheet above, the function interpolates one third of the way between the percentrank for 6.5 (=37.5%) and the percentrank for 8 (=50.0%). The resulting value, 41.6666666666667% is rounded down to 5 significant figures, as specified by the supplied [significance] argument.
Further examples of the Excel Percentrank.Inc function can be found on the Microsoft Office website
If you get an error from the Excel Percentrank.Inc function this is likely to be one of the following:
#N/A    Occurs if the supplied x is smaller than the minimum, or greater than the maximum value in the supplied array.  
#NUM!   

Also, the following formatting problem is encountered by some users:
If the result of your Percentrank.Inc function is presented as a decimal, or shows 0%, this is likely to be due to the formatting of the cell containing the function.
This can therefore be fixed by formatting the cell as a percentage, with decimal places :