You know there’s a white paper published by the CBOE that explains how the VIX is calculated, right? 

It’s simply just derived by calculating two different variances (i.e. squared differences from the mean option price) for two different expirations that are then averaged to get a 30-day variance*. This 30-day variance is then converted into a standard deviation by taking the square root of it. That standard deviation is then multiplied by 100, and, voila! - You have the “price” of VIX.

So, what happens when you square any number. You get something positive, right? What happens when you take the square root of any positive number? You get a positive number. So, VIX can’t go below zero. That’s the only hard limit.

(*of puts and calls on the S&amp;P 500 between 23 and 37 days out till expiration.)