0DTE Options: Mechanics, Risk, and Execution
Same-day options are now roughly half of all SPX volume, and most people trading them cannot state their settlement terms. This is the full picture: what the contract actually is (European, cash-settled, $100 multiplier, PM settlement), why the last trading day behaves unlike any other day because gamma scales as one over the square root of time remaining, what the research says about who actually makes money, and what execution genuinely requires. The mechanics are knowable. The variance is brutal. Both deserve to be stated plainly.