The Excel Chisq.Dist function calculates the Probability Density Function or the Cumulative Distribution Function for the ChiSquare Distribution.
The function is new in Excel 2010 and so is not available in earlier versions of Excel.
The syntax of the Chisq.Dist function is:
where the function arguments are:
x    The value at which the chisquare distribution is to be evaluated (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).  
cumulative    A logical argument that specifies the type of chisquare distribution to be calculated. This can be either:  

The above chart on the right shows the probability density function for the chisquare distribution with 1, 2 & 3 degrees of freedom.
If you want to calculate the value of any of these functions for a specified value of x, this can be done using the Chisq.Dist function.
For example, the value of the probability density function with 2 degrees of freedom, at x = 3 is calculated by the following function:
This gives the result 0.11156508.
The above chart on the right shows the ChiSquare Cumulative Distribution function with 1, 2, & 3 degrees of freedom.
If you want to calculate the value of any of these functions for a specified value of x, this can be done using the Chisq.Dist function.
For example, the chisquare cumulative distribution with 2 degrees of freedom, at the value x = 3, is calculated by the following:
This gives the result 0.77686984.
Further details and examples of the Excel Chisq.Dist function are provided on the Microsoft Office website.
If you get an error from the Excel Chisq.Dist function this is likely to be one of the following:
#NUM!    Occurs if either:

#VALUE!    Occurs if any of the supplied arguments are nonnumeric. 