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 infinity to x, of the Normal Probability Density function.
More information on the Normal Distribution is given on the Wikipedia Normal Distribution PageIn Excel 2010, the NORMDIST function has been replaced by the NORM.DIST function, which has improved accuracy.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.
The Excel NORMDIST function calculates the Normal Probability Density Function or the Cumulative Normal Distribution Function for a supplied set of parameters.
The format 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 which denotes the type of distribution to be used:

Normdist Function ExamplesExample 1  Normal Probability Density FunctionThe chart on the right shows the 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:
=NORMDIST( 50, 40, 20, FALSE )
This gives the result 0.017603266. 
Normal Probability Density Function with mean = 40, std. dev. = 20

Example 2  Cumulative Normal Distribution FunctionThe chart on the right shows the 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:
=NORMDIST( 0.8, 1, 0.3, TRUE )
This gives the result 0.252492538. 
Cumulative Normal Distribution Function with mean = 1, std. dev. = 0.3

Further information and examples of the Excel Normdist function can be found on 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 either the supplied mean or the supplied standard_dev argument is nonnumeric 