# Why does VIX need to calculate the Forward term?

From the reference, the Vix Whitepaper of CBOE, I found the formula of VIX.

There are two terms. The first one is focusing on the info from Option contracts. And the second one is focusing on the relationship between the forward index and strike price.

In addition, there is a part to illustrate the forward index.

I am confused with the purpose of the second term and the forward index.

I appreciate any help to explain that!

**Reference : https://www.cboe.com/micro/vix/vixwhite.pdf

forward index level 是用

call - put = forward算出来的，

call payoff - put payoff = forward payoff,

p=put price,

F 假设是T的 index level,

K是strike price,

Google Translation:

Forward index level is used

Call - put = forward calculated,

Call payoff - put payoff = forward payoff,

So the prices on both sides should be equal,

Use c=call price,

p=put price,

F is assumed to be the index level of T,

K is the strike price,

Then there should be c - p = e^{-RT} (F-K),

The right side of the equation is the pricing formula for forward.

Multiply e^{RT} on both sides to get the forward term.