Monday, November 26, 2012

Negative forward volatility

You can calculate the forward volatility between tenor 1, T1, and tenor 2, T2, using the formula below.

Consider: T2> T1

Vol T2-T1= (((VolT2^2*)*T2-(VolT1^2*)*T1)/(T2-T1))^(1/2)

This scheme is known as flat forward volatility interpolation.

How should we procedure if Vol T1>>> VolT2? In this case the argument of the function will be negative and it is not to calculate the SQRT.

This should normally not happen with fungible assetts like equity. It's instead very common in some commodities like natural gas where strong seasonality on term structures gives you negative fwd vol. In these cases you can't apply that formula, market is said to be incomplete.

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