Index Linked CDs
The example that I describe is not exactly a index-linked CD: I have used the SPY (Standard & Poor's Depositary Re.) as a proxy to the SP500.
Notations and valuesFigures used were market values on 2010/04/04
Assume you are investing 100.000 $ (rather than the one-dollar suggested by text-books).
The SPYlinked CDYou invest the present value of I , I/(1+Rf) in a bond , the future value of which is [ I/(1+Rf)]*(1+Rf)=I
What is left of your initial amount is invested in at-the-money call options.
Let us assume that eventually the SP500 index will increase by 10%, the SPY will increase by 10%, and your calls will then be worth 2.311. The terminal value of your investment will be equal to
The terminal value of the bond, I
The terminal value of the calls ( [I*Rf/(1+Rf)] / pr ) * Max [ (S-K) ; 0 ] In the worst case, the call will expired with no value, and you will have kept the value of your investment. In a better case, the value of one call will be (S-K) and your calls will be worth (S-K)*I*Rf / [ pr*(1+Rf) ] , your entire profit since the future value of the bond acquired will be your initial investment.
Your return will therefore be (S-K)*I*Rf / [ pr*(1+Rf) ] / I = (S-K)*Rf/ [ pr*(1+Rf) ]; If you had invested in stock, your profit would have been (S-So)/So. The multiplier of participation to the stock market increase is therefore = (S-K)*Rf / [ pr*(1+Rf) ] / [S-So)/So] , which can be rewritten as
So *Rf*(S-K)/ (S-So)*pr*(1+Rf)
If you buy calls that are exactly at-the-money, then K=So and the participation multiplier becomes So*Rf/ [pr * (1+Rf)].
In our example, we get a 2.49% increase when market increased by 10%, implicitly meaning a multiplier value of 24.9%.