It's a very unscientific method and better with higher volume options, but I can say what I do. Call up the CAT(SPY) chain for this weekly option. Look at open interest and figure where will the market makers be able to get the most options to close with no value. In this case you can see the most open interest, calls and puts, is at 103. So expect, whatever gyrations during the day, they would want to close at or near 103. This is of course if there are no drastic market reasons to move another direction. Actually the largest single open interest is 100 puts but I would not be worried about that. this is all JMHO.
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