Key Differences:The SPX is the S&P 500 index based on basis points. You cannot buy shares of the SPX index directly, only options. The SPY is an S&P 500 ETF that tracks the performance of the SPX index. You can buy and hold shares of SPY and trade options.Sizing:The SPX is 10x the size of the SPY. Therefore, one SPX options contract is worth 10 SPY contracts, allowing you to save on commissions.Tax Treatment:For SPX options, 60% of profits are taxed at long-term rates while 40% is taxed at short-term rates. The SPY equity and options are taxed like any other stock; any option profits held for less than one year are taxed at the short-term capital gains rate.Settlement, Dividends, and Full Context

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