The Excel LOGNORM.INV function calculates the inverse of the Cumulative LogNormal Distribution Function of x, for a supplied probability.
The Lognorm.Inv function is new in Excel 2010 and so is not available in earlier versions of Excel. However, the function is simply an updated version of the Loginv function that is available in earlier versions of Excel.
The syntax of the Lognorm.Inv function is:
Where the function arguments are:
probability    The value at which you want to evaluate the inverse function. 
mean    The arithmetic mean of ln(x). 
standard_dev    The standard deviation of ln(x). 
The above chart on the right shows the Inverse LogNormal Cumulative Distribution Function for a variable x. The mean of ln(x) = 2 and the standard deviation of ln(x) = 0.2.
If you want to calculate the value of x for a probability of 0.3, this can be done using the Excel Lognorm.Inv function, as follows:
This gives the result 6.653346076.
Further information and examples of the Excel Lognorm.Inv function can be found on the Microsoft Office website.
If you get an error from your Excel Lognorm.Inv function this is likely to be one of the following:
#NUM!    Occurs if either:

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