"Ben" wrote...
What is the actual equation used for the lognormdist function
(i.e. y = ...). The excel help files do not provide the exact
equation, instead only the function syntax are explained. I
have searched through several excel help book and online and
have not been able to find the actual equation

Online help for LOGNORMDIST is quite explicit that

LOGNORMDIST(x,m,s) = NORMSDIST((LN(x)-m)/s)

It's standard to define the density or distribution of log-transformed
random variables in terms of the untransformed density or distribution for
the log of possible values.

NORMSDIST is obscurely defined in terms of the normal density, which is the
derivative of the normal distribution. The normal distribution doesn't have
a closed form, meaning it can't be represented as a simple equation, only as
a definite integral. It's always derived numerically.