Understanding Put-Call Parity and Synthetics - Part Three
...continued from Part Two
Synthetics Cont...
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A short (negative) put is equal to a short (negative) call plus long stock, after the
basis adjustment. Consider that if the put is sold instead of buying stock and selling a call, the interest that would otherwise be paid on the cost of the stock up to the strike-price is a savings to the put seller. To balance the equation, the interest benefit of the short put must be added to the call side (or subtracted from the put side). It is the same with dividends.
The dividend benefit of owning the stock must be subtracted from the call side to make it equal to the short put side (or added to the put side to make it equal the call side). The same delta concept applies here. The short 50-strike put in our example would have a 0.45 delta. The short call would have a ñ0.55 delta. Buying one hundred shares along with selling the call gives the synthetic short put a net delta of 0.45 (ñ0.55
plus 1.00).
Short Call vs. Short Put + Short Stock
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Similarly, a synthetic short call can be created by selling a put and selling (short)
one hundred shares of stock. FIGURE 6.4 shows a conceptual overview of these two
positions at expiration. Put-call parity can be manipulated as shown here to illustrate the composition of the synthetic short call.
- ñCall = ñPut ñStock + Strike ñInterest + Dividend
liability to the married-put seller. To make all things equal, one subtracts interest and
adds dividends to the put side of the equation.
Comparing Synthetic Calls and Puts
The common thread among the synthetic positions explained above is that, for a put-call pair, long options have synthetic equivalents involving long options, and short options have synthetic equivalents involving short options. After accounting for the basis, the four basic synthetic option positions are:
- Long Call = Long Put + Long Stock
- Short Call = Short Put + Short Stock
- Long Put = Long Call + Short Stock
- Short Put = Short Call + Long Stock
efficient market will ensure that the implied volatility is closely related for both. For example, if a long call has an IV of 25 percent, the corresponding put should have an IV of about 25 percent, because the long put can easily be converted to a synthetic long call and vice versa.
The greeks will be similar for synthetically identical positions, too. The long options and their synthetic equivalents will have positive gamma and vega with negative theta. The short options and their synthetics will have negative gamma and vega with positive theta.
to be concluded in PART FOUR
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About Dan Passarelli
Dan Passarelli, is the author of the book Trading Option Greeks and the president of Market Taker Mentoring LLC. Market Taker Mentoring provides personalized one-on-one mentoring for option traders. Dan started his trading career on the floor of the Chicago Board Options Exchange (CBOE) as an equity options market maker. He also traded agricultural options and futures on the floor of the Chicago Board of Trade (CBOT). In 2005, Dan joined CBOE’s Options Institute and began teaching both basic and advanced trading concepts to retail traders, brokers, institutional traders, financial planners and advisors, money managers, employees of the SEC and Federal Reserve bank, and market makers. In addition to his work with the CBOE, he taught options strategies at the Options Industry Council (OIC). Dan has been featured on television and radio and has written numerous articles in the financial press. Dan can be reached at dan@markettaker.com. He can be followed on Twitter.
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