EO (sorry if that sounded like Tusshar Kapoor in Golmaal ...
),
The way I look at things (maybe option experts can comment on how far from the truth I am) is as follow ...
Premium value = Intrinsic value + "Zing" factor
Intrinsic value is the std definition - how much in the money the option is right now. It is 0 for out of money options.
"Zing" factor is simply the probability of this option being ITM anytime before expiry.
Now this probability has many of the variables you listed out but the main ones are
- The measured volatility of the stock/index. This implies how much it typically "travels" in a day.
- The measured volatility prevailing currently in the market as a whole. This is available on NSE called India VIX. This take cares of factors like events coming like RBI announcements, the fear factor etc.
- How far off the strike price is from the current price
- The current "acceleration" of the price towards the strike price.
Now assuming these variables dont change, the socalled "time value" or "zing" factor of an option is a function of days to expiry. The extra premium you are paying besides the intrinsic value divided by number of trading days to expiry should give you the "time decay".
Take our favourite SBI 2800 call. It closed around 61. It is not yet ITM but nearly there. So intrinsic value is 0. If the stock price stays around the current closing, you can expect it to decay by 61/9 (around 6.75) the next day. (9 trading days remaining). This is my very simplistic approach to time decay.
The things to consider are
- "Acceleration" towards the strike price is a very important consideration for just OTM calls. You are almost always better off dumping options during a price surge. I dumped this SBI call at 67 during the first surge after the RBI announcement. The option price peaked out at 68 that time, the news settled and then the stock retraced and again made another run. This time the option price peaked out at around 72. For intraday players, the end of these surges are good place to dump options.
- I like to divide by trading days since I think anyway everyone knows about trading holidays. The theoretical calculators may treat this differently.
- Theory tells that options decay at the speed of square root of time remaining. Hence the decay will be faster as we come closer to expiry, it will not be constant at 61/9 in the above example.
- Keep a watch on India VIX. Buying options when it is very high (above 23 or so in the recent year or so) may mean that we are paying very high price because of the market conditions and if the news that the market is awaiting comes (whether it be good or bad) , the volatility will dampen off.
Finally, if you really want to get into calculating option greeks, then Option Oracle is a pretty good software. The "theta" calculated by that software is the "time decay" in theory. But hoping we get our hands on SG's Excel soon.
All the resident option experts, please correct me !
Regards,
E.
My question is: how do I corelate all (or some) of these variables (please point out if I missed something), so as to calculate the Time Decay on fly in order to safely figure out my exit point?