For long option value (money you pay) we create a credit in the PC Span calculation and for short option value (money you collect) we create a debit. This way you are getting credit against the margin (span risk) calculation for the money that you have already paid out. Long option value is always greater than the span risk that is calculated because we understand that you cannot lose more than what you have paid for a long option. For a short option we create a debit because we want to make sure that you are keeping the premium for that option in the account until you unwind the position or it expires. In other words, a short option will also have additional margin that has to be posted that is not covered by the premium collected.
Additionally, if you have a short deep-out-of-the-money option, CME applies a Short Option Minimum (SOM) to the position. This is because deep-out-of-the-money short options may show zero or minimal Scan Risk given the price and volatility moves in the 16 market scenarios, yet still present risk in the event that these options move closer-to-the-money or in-the-money, thereby generating potentially large losses. Hence CME applies the SOM to each product to account for this potential exposure. Note that if the Scan Risk is lower than the Short Option Minimum, the SOM is charged.
CME Group is the world's leading and most diverse derivatives marketplace. The company is comprised of four Designated Contract Markets (DCMs). Further information on each exchange's rules and product listings can be found by clicking on the links to CME, CBOT, NYMEX and COMEX.