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Do options always expire on third Friday of every month
Prior to 2005, the only SPY options that existed were the monthly ones that expire on the third Friday of every month.  But in 2005, the Chicago Board Options Exchange introduced SPY weekly options that expire every Friday (except that there is no weekly option that expires on the same day as a monthly option).  These weekly options only exist for 8 days - they start trading on a Thursday and expire 8 days later on Friday. The SPY options that expire on Friday October 31 are weekly options, and they started trading on Thursday October 23. Sources: Investopedia