This page only explains how 0DTE expiry day settles and how the simulator handles the close. It gives no directional advice and predicts nothing. Quotes are delayed about 15 minutes, for paper practice only — not real-time quotes, not investment advice.
0DTE means the expiry date is today: the contract is only valid for the day and no longer exists after the close. The next day brings a new set of expiring contracts, not a continuation of the same ones. Practice is measured in Eastern days, and the discipline counters reset on the Eastern date.
SPX is an index option, so expiry settles in cash with no shares changing hands: an in-the-money contract settles on the cash difference between the settlement price and the strike, and an out-of-the-money contract expires worthless. For a Call, the in-the-money part is the settlement price above the strike; for a Put, it is the strike above the settlement price. Anything short of in-the-money produces no settlement cash.
SPX index options are European-style: they can only be exercised at expiry, not early like American-style options. Before expiry, a position's changing value shows up only in its price; at expiry, the settlement price fixes the outcome.
The simulator never auto-closes. Its close rules prompt you to act yourself: no new positions after 15:30 ET, and after 15:55 ET the page prompts you to close the day's positions and offers a close-all button. The decision stays with you. Prices move fastest into the close, and the post-15:30 ban on new positions exists to keep you out of the hardest stretch to price.
Fees are $0.65 per contract per side, and all P&L is shown net of fees; the daily fee circuit breaker trips at $60. Margin locked on selling to open is a simplified simulator convention of 20% of strike — not a broker's real margin requirement — and is released on close.
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