"0DTE" means zero days to expiration — an option traded on the day it expires (and by extension the broader family of short-dated weekly/daily options). Because an option's gamma, theta, and charm all spike as time-to-expiry collapses toward zero, 0DTE contracts behave very differently from longer-dated options: a small move in the underlying can swing the position from worthless to deep-in-the-money within minutes, and the dealers who sit on the other side may have to hedge that convexity aggressively. The central question this topic addresses is whether the explosive growth of 0DTE volume — now a majority of all SPX options traded — meaningfully reshapes intraday price action, or whether the flows are balanced enough that the effect is largely cosmetic. The honest answer is contested, and the mechanics matter more than any single headline.

How it's formed

The "0DTE effect" is a second-order consequence of options Greeks under extreme time compression, transmitted to the underlying through dealer (market-maker) hedging:

• Gamma (rate of change of delta) is largest for at-the-money options near expiry. With only hours left, an ATM 0DTE contract's gamma can be several multiples of an equivalent weekly's — practitioner write-ups commonly cite roughly 2–5x, though the exact ratio depends on volatility and time of day.
• Dealer gamma sign drives the feedback direction. If dealers are net short gamma (they sold the options the public bought), staying delta-neutral forces them to buy as price rises and sell as it falls — a pro-cyclical, move-amplifying flow. If dealers are net long gamma, they sell rallies and buy dips — a counter-cyclical, dampening flow that produces "pinning" near heavily-traded strikes.
• Charm (delta decay over time) becomes a force into the close. As expiry approaches, the deltas of away-from-money options bleed toward zero, so dealers unwind hedges — a documented contributor to the end-of-day "pin" toward high-open-interest strikes and to occasional late-day accelerations.
• Theta decay is non-linear intraday: slow in the morning, accelerating sharply after early afternoon, which is why 0DTE option prices and the urgency of hedging both intensify late in the session.

The key conditioning variable is net dealer positioning, not gross volume. Gross 0DTE volume can be enormous while net dealer exposure stays tiny if customer buying and selling roughly offset.

How it's used in practice

Three broad camps consume short-dated options effects:

• Directional / lottery buyers (largely retail) buy 0DTE calls or puts for cheap, high-convexity intraday exposure. CBOE notes retail makes up roughly half of SPX 0DTE volume.
• Premium harvesters / systematic sellers sell 0DTE spreads, iron condors, or run programs (including some ETFs) to collect the rapid theta decay, accepting tail risk.
• Flow/positioning analysts estimate aggregate dealer gamma exposure (GEX) and key strikes from open interest to anticipate whether the tape is likely to be "sticky" (long-gamma, mean-reverting, pinned) or "slippery" (short-gamma, trend-amplifying). Vendors such as SpotGamma popularized this lens. These estimates are models — sign and magnitude depend on assumptions about who is long vs. short each strike, which is not directly observable.

In practice the most reliable, least-disputed pattern is end-of-day mechanics: charm-driven pinning toward large-OI strikes and the potential for a sharp move if a pin breaks late. Effects are generally episodic — most pronounced when flow is one-sided, liquidity is thin, and dealers are short gamma at a critical level.

Adoption, debate & evidence

Adoption is enormous and recent. CBOE reports SPX 0DTE rose from roughly 5% of SPX options volume in 2016 to a record ~62% in August 2025, averaging around 2.3 million contracts/day (~59% of SPX volume) in 2025; across all U.S. listed options 0DTE was about 24% of volume in 2025. The growth inflected after Tuesday/Thursday SPX expiries were added.

Whether 0DTE destabilizes markets is a genuine, unsettled academic dispute:

• "Largely benign" camp. CBOE's own research finds no evidence 0DTE amplifies intraday volatility: close-to-close vs. intraday realized vol is in line with history, dealer net gamma is tiny relative to S&P futures liquidity (CBOE cites on the order of 0.04%–0.17%), and balanced two-sided customer flow keeps net dealer exposure small. Dim, Eraker & Vilkov (2023/24) find dealers' net gamma is on average positive and that intraday 0DTE volume shocks do not propagate or amplify past returns — positive gamma strengthens reversals.
• "Destabilizing" camp. Brogaard, Han & Won report that a one-standard-deviation increase in 0DTE trading raises volatility by roughly 9% relative to its mean, an effect that persists even after controlling for dealer gamma hedging — implying channels beyond mechanical hedging.

These results are not fully reconcilable, partly because dealer positioning is estimated, not observed, and the studies use different windows and identification. The defensible synthesis: aggregate average effects appear small and close-to-close volatility has not structurally risen, but conditional, intraday episodes (one-sided flow into a short-gamma regime, especially late-day) are real — consistent with the August 5, 2024 and similar single-session air pockets. Treat "0DTE is fueling a crash" claims as folklore unless the positioning data supports it.

Strengths & limitations

Where the lens helps: identifying high-OI strikes likely to act as intraday magnets; flagging short-gamma regimes where breakouts/breakdowns may run further than fundamentals justify; understanding why late-session reversals and pins recur.

Where it fails:

• Net positioning is unobservable. GEX/dealer-gamma estimates infer the dealer's side of each strike; if the inference is wrong, the predicted dampening/amplifying flips. This is the single most common misuse — treating a vendor GEX number as ground truth.
• Gross volume ≠ impact. Huge 0DTE volume with balanced flow nets to near-zero dealer hedging. Reasoning from volume alone overstates the effect.
• Regime- and time-dependent. Effects concentrate in episodic, thin-liquidity, one-sided conditions and into the close; most of the day they are negligible.
• Reflexive and fast. Even when present, hedging flows are an intraday phenomenon measured in minutes-to-hours — not a multi-day signal, and largely irrelevant to swing or position horizons except as a same-day entry/exit timing nuance.

Sources

• CBOE, Volatility Insights: Evaluating the Market Impact of SPX 0DTE Options — finds no evidence of intraday vol amplification; net dealer gamma ~0.04%–0.17% of S&P futures liquidity.
• CBOE Insights — SPX 0DTE Options Jump to Record 62% Share in August; State of the Options Industry 2025 — volume/share growth, retail ~53% of SPX 0DTE flow, ~24% of all U.S. options.
• Dim, Eraker & Vilkov (2023/24), 0DTEs: Trading, Gamma Risk and Volatility Propagation (SSRN 4692190) — net gamma on average positive; intraday volume shocks do not propagate; selective (not unconditional) timing opportunities.
• Brogaard, Han & Won, Does 0DTE Options Trading Increase Volatility? (SSRN 4426358) — ~9%-of-mean vol increase per 1 SD of 0DTE trading, robust to gamma-hedging controls. Disputes the CBOE/Dim findings.
• Adams, Dim, Eraker, Fontaine & Ornthanalai (2024), Do S&P500 Options Increase Market Volatility? Evidence from 0DTEs (SSRN 5641974) — volatility lower on days 0DTE available; effect tied to dealer gamma sign/magnitude (max ~6.4 pp impact on 30-min annualized vol).
• SpotGamma — Vanna and Charm Explained; 0DTE Options Explained — charm-driven end-of-day pin, dealer hedging mechanics (practitioner source; estimates).
• Schwab, Zeroing in on 0DTE Options — definitions and basic mechanics.

Flagged dispute: the academic literature is genuinely split on whether 0DTE destabilizes intraday volatility (CBOE/Dim et al. say no; Brogaard et al. say yes). Practitioner GEX/charm claims rely on unobservable dealer positioning and should be treated as estimates.