Term Structure of Volatility
Term structure of volatility—also called monthly skew or horizontal skew
—is the relationship among the IVs of options in the same class with the
same strike but with different expiration months. IV, again, is often
interpreted as the market’s estimate of future volatility. It is reasonable to
assume that the market will expect some months to be more volatile than
others. Because of this, different expiration cycles can trade at different IVs.
For example, if a company involved in a major product-liability lawsuit is
expecting a verdict on the case to be announced in two months, the one-
month IV may be low, as the stock is not expected to move much until the
suit is resolved. The two-month volatility may be much higher, however,
reflecting the expectations of a big move in the stock up or down,
depending on the outcome.
The term structure of volatility also varies with the normal ebb and flow
of volatility within the business cycle. In periods of declining volatility, it is
common for the month with the least amount of time until expiration, also
known as the front month, to trade at a lower volatility than the back
months, or months with more time until expiration. Conversely, when
volatility is rising, the front month tends to have a higher IV than the back
months.
Exhibit 3.3 shows historical option prices and their corresponding IVs for
32.5-strike calls on General Motors (GM) during a period of low volatility.
EXHIBIT 3.3 GM term structure of volatility.
In this example, no major news is expected to be released on GM, and
overall market volatility is relatively low. The February 32.5 call has the
lowest IV, at 32 percent. Each consecutive month has a higher IV than the