To be able to calculate the volatility of the spread, we must equalize the volatilities of the individual options. First, let’s move the June calls by moving June’s implied volatility down from 40 to 36, a decrease of four volatility ticks. Four volatility ticks multiplied by a vega of .05 per tick gives us a value of $.20. Next we subtract $.20 from the June 70 option’s present value of $2.00 and we get a value of $1.80 at 36 volatility. Now the two options are valued at an equal volatility basis. Looking at this first adjustment where we moved the June 70′s volatility down to 36 from 40, we have a value of $1.80 at 36 volatility. The August 40 call has a value of $3.00 at 36 volatility. So the spread will be worth $1.20 at 36 volatility. If y african mango ou wanted to move the August 70 calls instead, you would take the August 70 call vega of .08 and multiply it by the four tick implied volatility difference. This gives you a value of $.32 that must be added to the August 70 call’s present value in order to bring it up to an equal volatility (40) with the June 70 call. Adding the $.32 to the August 70 call will give it a $3.32 value at the new volatility level of 40 which is the same volatility level as the June 40 calls. Now, our spread is worth $1.32 at 40 volatility. August 70 calls at $3.32 minus the June 70 calls at $2.00 gives the price of the spread at 40 volatility. It does not make any difference which option you move. The point is to establish the same volatility level for both options.