SPX vs SPY for 0DTE Trading: Settlement, Exercise, Size, and Taxes
SPX and SPY both track the S&P 500, and for a 0DTE trader they are not the same instrument. The differences in settlement, exercise style, contract size, and tax treatment are large enough to change your after-tax return and your assignment risk. This is the complete side-by-side, including the two options most comparison pages leave out and an honest account of who SPX is actually wrong for.