0DTE and SPX trading

What actually changes on expiry day

The Greeks that barely matter on a 30-day option dominate a 0DTE. Three of them change character completely.

Gamma goes near-vertical

As expiry approaches, an option's delta stops being a smooth curve and starts resembling a step function. A contract sitting $2 out of the money at 2:00pm might have a delta of 0.15; if price moves through the strike, delta races toward 1.00 within minutes. This is why a 0DTE can go from down 60% to up 200% inside a single fifteen-minute candle — and why it can do the reverse.

Theta stops being linear

Time decay is often described as steady erosion. On the final day it is not. Extrinsic value collapses fastest in the last two hours, and by the close every out-of-the-money contract is worth exactly zero. There is no overnight hold, no recovery, no waiting for the thesis to work.

Vega mostly stops mattering

With hours left, there is almost no time value for implied volatility to inflate. A volatility spike that would rescue a 45-day position does very little for a 0DTE. The trade is close to a pure directional bet on the underlying over a very short window.

Why SPX rather than SPY

	SPX	SPY
Style	European — no early exercise	American — assignable early
Settlement	Cash	Physical delivery of shares
Assignment risk	None	Real, especially on short legs
Dividend risk	None	Early assignment around ex-div
Contract size	~10× SPY notional	Smaller, more granular
US tax treatment	Section 1256, 60/40 split	Standard short-term

The practical points are cash settlement and no assignment. On a same-day expiry, being assigned shares you did not want is a genuinely bad outcome, and SPX removes that category of problem entirely. The Section 1256 treatment — 60% of gains taxed at long-term rates regardless of holding period — is a meaningful edge for active US traders, though it is a question for your accountant rather than for us.

The trade-off is size. One SPX contract carries roughly ten times the notional of one SPY contract, which makes precise position sizing harder on smaller accounts. Run the numbers before assuming you can trade it.

Where dealer positioning fits

0DTE volume is now a large share of total SPX options volume, which means dealer hedging of those contracts is itself a significant driver of intraday price. This is the part that makes the instrument tradeable rather than random.

Above the gamma flip, dealers are long gamma and their hedging suppresses movement — price grinds and pins toward large strikes. Below it, hedging amplifies moves and the same setup that failed all morning starts running. Marking the flip level and the call and put walls before the open is the difference between trading a 0DTE and gambling on one. See gamma exposure explained for the mechanism.

Four ways people lose money on 0DTE

• Sizing off account percentage instead of premium. Risking 2% of the account is a reasonable rule when a stop protects you. On 0DTE, gap risk and spread blowouts mean the realistic worst case is often the full premium. Size assuming you lose all of it.
• Averaging down. Adding to a losing 0DTE is adding to a position whose remaining time value is measured in minutes. Almost nothing recovers it except being right immediately.
• Ignoring the spread. A contract quoted 1.20 / 1.35 costs you roughly 12% of premium on a round trip before the trade does anything. Deep out-of-the-money strikes late in the day are frequently untradeable at any sensible price.
• Holding into the last thirty minutes without a plan. Extrinsic value is gone and the position becomes a binary. Some desks trade that deliberately; most people arrive there by accident.

How the desk trades it

The SPX side is run on a narrow set of repeating levels rather than a hunt for new setups. Gamma levels are marked before the open. During the session we wait for price to reach one with a liquidity sweep or imbalance behind it. If that happens, the alert goes out with the stop already stated. If it does not, there is no trade — most marked levels are never touched, and a flat day is a normal outcome. Full process on the methodology page, and the results, including stop-outs, on the record.

Should you trade 0DTE at all

Honestly: probably not as a beginner. The instrument punishes hesitation, imprecise entries and loose sizing more harshly than anything else in retail options, and the feedback loop is fast enough to drain an account in weeks. If you are learning, longer-dated contracts on the same levels teach the same lessons at a survivable speed. The levels are the skill; 0DTE is just the highest-leverage way to express them.