re: Vol challenge a hard one In my book GypsyKing and AK47 are...

re: Vol challenge a hard one In my book GypsyKing and AK47 are correct when they say it is a known problem.

You have
y = f(x, z, ...)
You can't arrive at an inverse function g such that
x = g(y, z, ...)

So you have to use numerical approximation such as Newton-Raphson, Runge-Kutta or some such method. No doubt this is what Excel goal seek does. In other words, as Gypsy and AK47 said, you just plug a few vols into model until answer equals market price close enough.

You won't solve it analytically Remmers, ie no one cell formula unless you call a VBA function that does the approximation.