The Excel Chisq.Dist.Rt function calculates the righttailed probability of the ChiSquare Distribution
The function is new in Excel 2010 and so is not available in earlier versions of Excel. However, the Chisq.Dist.Rt function is simply an updated version of the Chidist function, which is available in earlier versions of Excel.
The syntax of the Chisq.Dist.Rt function is:
where the function arguments are:
x    The value at which you want to evaluate the chisquare distribution (must be ≥ 0). 
degrees_freedom   
The number of degrees of freedom (must be an integer between 1 and 10^{10}). (If the supplied value is a decimal, this is truncated to an integer). 
The above chart on the right shows the righttailed chisquare distribution, with 1, 2 and 3 degrees of freedom.
The value of any of these distributions, for a specified value of x can be calculated using the Excel Chisq.Dist.Rt function. Examples are shown in the spreadsheets below:
Formulas:

Results:

For further examples of the Excel Chisq.Dist.Rt function, see the Microsoft Office website.
If you get an error from the Excel Chisq.Dist.Rt function this is likely to be one of the following:
#NUM!   
Occurs if either:

#VALUE!    Occurs if either of the supplied arguments is nonnumeric. 