One of the best signals we track is short term contango. The Contango reading measures the slope of the at-the-money implied volatilities from short term expirations.
We have found that the term structure implied volatility skew is often kinked about 45 days out. For expirations greater than 45 days a more rational term structure is normally observed.
Short term implied volatility is also more important for use in signals because those traders in the know will get more leverage using shorter term options. This is why we track this reading so closely.
A similar analysis could come from looking at constant maturity readings, like 10-day implied volatility (called iv10d in our API) to 20-day and 30-day. The problem with using constant maturity to make contango calculations is that there are not as many observations, and constant maturity has already weighted the around the days to expiration implied volatility to make the reading.
Contango is when the shorter implieds are below the longer implieds. This is the normal state of affairs for the options market happening 72.5% of the days since 2007. The flipside of contango is backwardation. Backwardation is when the short term IVs are greater than the long term.
What we see sometimes is that when contango flips to backwardation, it is usually already bad or going to get bad for the market.
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