The Normal distribution is a continuous probability function that is given by the formula:
where μ is the mean of the distribution, σ^{2} is the variance, and x is the independent variable for which you want to evaluate the function.
The Cumulative Normal Distribution function is given by the integral, from ∞ to x, of the Normal Probability Density function.
For more information on the Normal Distribution, see the Wikipedia Normal Distribution Page.In Excel 2010, the Normdist function has been replaced by the Norm.Dist function, which has improved accuracy.
Although it has been replaced, the Normdist function is still available in Excel 2010 (stored in the list of compatibility functions), to allow compatibility with earlier versions of Excel.
However, the Normdist function may not be available in future versions of Excel, so it is advised that you use the Norm.Dist function if possible.
The Excel NORMDIST function calculates the Normal Probability Density Function or the Cumulative Normal Distribution. Function for a supplied set of parameters.
The syntax of the function is:
Where the function arguments are:
x    The value at which you want to evaluate the distribution function.  
mean    The arithmetic mean of the distribution.  
standard_dev    The standard deviation of the distribution.  
cumulative   
A logical argument specifying the type of distribution to be used:

The chart on the rightabove chart shows the Normal Probability Density Function with a mean of 40 and a standard deviation of 20.
If you want to calculate the value of this function at x = 50, this can be done using the Excel Normdist function, as follows:
This gives the result 0.017603266.
The chart on the rightabove chart shows the Cumulative Normal Distribution Function with a mean of 1 and a standard deviation of 0.3.
If you want to calculate the value of this function at x = 0.8, this can be done using the Excel Normdist function, as follows:
This gives the result 0.252492538.
For further details and examples of the Excel Normdist function, see the Microsoft Office website.
If you get an error from the Excel Normdist function this is likely to be one of the following:
#NUM!    Occurs if the supplied standard_dev argument is ≤ 0. 
#VALUE!    Occurs if any of the supplied arguments is nonnumeric or is a nonlogical value. 