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Calculating probabilities using the VIX (aka "manual labor")


The interesting article below shows how to calculate the expected SPX range 30 days into the future using the vix...

seekingalpha.com/article/191161-practical-use-of-vix-for-s-p-500-investors


I'm fairly sure ThinkorSwim's "automatic" calculation is the same (note: all option-type software/brokers should be able to provide the same info instantly)...

ThinkorSwim's "80% 30-day" range    (click to enlarge) 



Note that the downside 10% probablity is slightly closer (79 pts vs 82) and this reflects the "skew" in implied volatilities in options.