Im used to options expiring on the third Friday of each month. Why do VIX options expire on a Wednesday?
VIX was designed to be a consistent, 30-day benchmark of expected market volatility, as measured by SPX option prices. Of course, there is only one day in the life of any option that is exactly 30 days to expiration, so in order to arrive at the 30-day standard, VIX is calculated as a weighted average of options expiring on two different dates. One day each month, on the Wednesday that is thirty days prior to the third Friday of the following calendar month, the SPX options expiring in exactly 30 days account for all of the weight in the VIX calculation. VIX options settle on these Wednesdays in order to facilitate the special opening procedures that establish opening prices for those SPX options used to calculate the exercise settlement value for VIX options.
