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IB sent this out, this week: Customers with Short Option Positions If you are short the options, you may be assigned until 5:30 pm based on the decisions to exercise by other market participants. These traders will have the ability to see the current market price after the close of options trading, at a time when you will not be able to close your option position. Again, these stocks may move significantly the after the close of regular trading at 4pm. This may mean that a position that was well out of the money at 4 pm may be in the money, perhaps significantly, by the time it is exercised against you. There is no way to predict whether the long holder of the option will exercise based on the 4:00 pm (16:00 price) or some later price up to 5:30 pm (17:30). The only way to avoid this volatility is to close out your short option position before 4 pm. To repeat, the only way to mitigate the uncertainty of your post-expiration stock position is to close out short positions prior to the end of the trading session. Interactive Brokers Client Services