I am selling strangles in S&P and Nasdaq with about a month to expiration and deltas between 0,05 and 0,10. I am particularly interested in figuring out how the option prices change in relation to time, keeping the delta constant. For instance, the 1940 May Call has a delta of 0,10. What will the price of a 0,10 delta 20 days from now be, assuming the VIX is unchanged from the current levels? I would appreciate any help
A basic option calculator will let you adjust time to expiration, price (of the underlying) and volatility and show you the resulting option price and greeks. You can find one here (image): There is a similar calculator on the CBOE site which allows you to punch in the ticker symbol, populating the stock price field and giving you you an instrument-specific drop down menu for expiration dates. Both the CBOE and OIC calculators are from ivolatility.com
Thanks but my issue here is not to adjust the price, but to see how the time decay affects the price of the option, if we keep the delta constant. An appropriate excel model surely would be a solution...
its your theta - that is the measure for the time decay. Just understand it is not linear and the theta value changes every day, so you cant just multiply todays value by 20 but the simplest easiest thing is use a model and step it forward.
If you're looking for risk to strike then calc the atm value against the prem you sold. You'll need to use some sort of sticky strike model or use the current skewed vola for the put when it goes atm.
May I reiterate my suggestion? Excel + basic Black-Scholes = Much joy and happiness This might help: http://www.espenhaug.com/black_scholes.html