0DTE mechanics

Definition

0DTE (zero days to expiration) options expire the same session they are traded. Since daily index expirations listed (SPX/SPY every weekday from 2022), same-day contracts have grown to a large share of index options volume — Cboe statistics have put 0DTE around 40%+ of SPX volume in recent years. Everything about options is compressed into hours: theta decays in minutes, gamma is at maximum, IV becomes an intraday event price, and every position is also a hold-to-expiry decision (mgmt-hold-to-expiry).

How it works / structure

• Greeks at time-zero scale: ATM gamma is enormous (deltas swing 0→±1 on small moves — greek-gamma at its limit); theta is the session itself; charm and speed (opt-second-order-greeks) operate on minutes; vega is small in level terms but IV moves discretely around intraday events.
• Premium structure: absolute premiums are small, percentage moves in premium are extreme — a 0DTE contract routinely does ±100-500% intraday; win/loss distributions are near-binary at the strike (expected_move_pct at daily tenor is the reference frame).
• Engine-executable parameters: entry time window, strike distance (delta or expected-move fraction), defined-risk mandate (the platform treats undefined-risk 0DTE shorts as requiring scenario-based sizing at gap severity — risk-scenario-analysis), hard session exit time, and the settlement style of the vehicle (SPX cash-settled European vs SPY physical American — different afternoon mechanics, ms-expiration-exercise-assignment).
• Market-structure debate: whether dealer 0DTE gamma hedging amplifies or dampens intraday index moves is actively researched and unsettled — the platform records the question, not a verdict.

When it applies

Intraday event expression (scheduled data at known times — CPI/FOMC days concentrate 0DTE activity, event-fomc, event-cpi); defined-risk same-day structures (verticals, iron condors at daily tenor); spread-of-hours theses in strategy-day-trading-styles universes. Data fidelity: replay requires intraday bars at minimum; daily bars cannot grade 0DTE claims — an engine-enforced constraint.

Risk profile & failure modes

• Gamma binary: near-the-strike positions in the final hour resolve like coin flips with leverage; “small premium” reads as small risk and is not (short side: the premium is small BECAUSE the tail is same-day).
• No recovery window: multi-day theses can be early; 0DTE theses cannot — timing error IS thesis failure.
• Friction share: spreads are pennies but premiums are pennies too; friction as a share of premium is the highest on the board (ms-bid-ask-spread).
• Documented retail losses: Beckmeyer et al (2023, working paper — labeled) estimate aggregate retail 0DTE losses after costs; direction of the finding aligns with the day-trading evidence base (strategy-day-trading-styles).

Evidence & limits

Volume growth and product mechanics are Cboe-documented. The academic literature is young: the retail-loss working paper is flagged as not-yet-peer-reviewed; dealer-flow amplification research is unsettled. The Greeks-at-limit behavior is mathematics. Marketed 0DTE “income systems” citing win rates without tail accounting are folklore, labeled.

Falsifiable-thesis examples

Illustrations only, not signals:

• “SPX will close inside today’s open ±0.8× the morning-priced expected move (0DTE iron condor thesis)” — falsified at the close.
• “A defined-risk 0DTE condor program (entry 10:00, exit 14:30, wings at 1.2× expected move) is net profitable after friction this quarter in intraday replay” — falsified by the replay P&L.

Cross-references

• The Greeks at their limits: greek-gamma, opt-second-order-greeks, greek-theta
• The daily reference frame: opt-expected-move
• Calendar concentration: event-opex, event-fomc, event-cpi
• The style family: strategy-day-trading-styles; settlement mechanics: ms-expiration-exercise-assignment