Most software packages that report option greeks (e.g., delta, gamma, theta, implied volatility) report incorrect values for VIX options. Depending on the date and state of the market they can vary from almost correct to widely wrong–giving truly nonsense numbers. These packages assume that the VIX index is the underlying for the VIX options. This is wrong. The true underlying is the corresponding VIX future for that month (e.g., January VIX futures for January VIX options).
You can compute reasonably accurate Greek values for VIX options yourself. You don’t even have to get a futures quote (although you can get delayed quotes for free). It turns out that if you add 10 to the $10 strike VIX option you are pretty close to the true price for the underlying volatility futures. Since the bid / ask spreads for these options tends to be pretty wide, you should split the the bid/ask price. This should get you within +-.15 of the true price. Then you can use options calculators to compute your IV and other greeks based on the underlying price and option price. One example :
| VIX Index | True VIX option underlying (volatility future) | |
| Underlying | 24.40 | 24.55 |
| Delta | .86 | .91 |
| Gamma | .11 | .09 |
| IV | 143 | 82 (correct number) |
