"0DTE" shows up constantly in options commentary now, usually attached to a claim about why the market did something dramatic in the final hour of trading. Strip away the drama and there's a specific, well-understood mechanical reason 0DTE options behave differently from a 30- or 60-day contract: gamma. This post walks through what 0DTE means, why its gamma profile is fundamentally different, and why that compresses hedging effects into hours instead of days.
What "0DTE" Actually Means
0DTE stands for "zero days to expiration" — an option contract that expires on the same calendar day it's being traded. Index options on the S&P 500 (SPX) have had Friday-expiring weeklies for years, but since 2022 the CBOE has listed SPX expirations on every trading day of the week, meaning a genuine 0DTE contract now exists Monday through Friday, not just at the end of the week.
The practical effect: on any given trading day, there's a full options chain — calls and puts across a wide range of strikes — that will stop existing at the closing bell. Exchange and industry reporting has repeatedly noted that 0DTE contracts make up a substantial share of total SPX options volume, at times cited well above a third of the day's activity. The exact share moves around with market conditions, but the structural point holds regardless of the precise number: same-day expiry is no longer a niche corner of the options market.
Gamma Compresses As Expiration Approaches
Gamma measures how much an option's delta changes for a $1 move in the underlying. For options with weeks or months left, gamma near the money is moderate and spread across a fairly wide range of strikes — plenty of time value left, plenty of uncertainty about where the stock finishes.
As expiration approaches, that picture changes sharply for options sitting close to the current price. Time value decays (theta accelerates), but for strikes right at the money, gamma actually increases — sometimes dramatically — because the option's fate (finish in-the-money or worthless) becomes a coin-flip decided by small moves in the final hours. Strikes even a little away from the money see the opposite: gamma collapses toward zero, because the option is now very likely to expire either deep in-the-money or worthless, with little sensitivity left.
The result is a gamma profile that's extremely peaked: enormous right at the money, negligible everywhere else. A 30-day chain spreads gamma exposure across a wide band of strikes; a 0DTE chain concentrates it into a narrow window around the current price.
A Concrete (Illustrative) Walkthrough
Numbers make this easier to see. These are illustrative, not live market data.
Suppose SPX is trading at 5,000. A 30-day at-the-money call might carry a gamma of roughly 0.003 per point (per contract, before the $100 index multiplier). A same-day, at-the-money call on the same underlying might show a gamma closer to 0.03 — an order of magnitude higher, and tightly clustered around the 5,000 strike rather than spread across the chain.
Now say a dealer is short 1,000 contracts of that 0DTE call (having sold them to buyers earlier in the session) and is hedging by holding a long position in the underlying equal to the position's delta. At a delta of 0.50, that's 1,000 × 100 × 0.50 = 50,000 index-equivalent units held long.
If SPX rallies 10 points intraday, the 0DTE call's delta — using the 0.03 gamma — moves from 0.50 to roughly 0.80. The dealer now needs 1,000 × 100 × 0.80 = 80,000 units, meaning they must buy an incremental 30,000 units into the rally, within that same session, just to stay hedged.
Run the same 10-point move through the 30-day option's 0.003 gamma: delta moves from 0.50 to only about 0.53, requiring an incremental purchase of just 3,000 units. Same underlying move, same starting position size — a full order of magnitude difference in the forced hedging flow, purely because of how close the option is to expiring.
Why Market Makers Hedge Differently Intraday
Because 0DTE gamma is so concentrated and time value is evaporating within hours rather than weeks, dealers holding 0DTE inventory can't hedge once a day and walk away — they rebalance continuously, often multiple times an hour, to stay close to delta-neutral as the underlying moves and as gamma itself keeps changing shape through the session.
This creates a feedback dynamic. If a dealer is net short 0DTE gamma (having sold more options than they bought), every uptick forces them to buy more of the underlying to re-hedge, and every downtick forces them to sell — hedging flow that pushes in the same direction as the move, rather than against it. When realized intraday volatility runs hotter than what was priced into the options, that dynamic can compound: the dealer ends up buying into strength and selling into weakness more aggressively than a calmer session would require, amplifying the very move being hedged.
None of this is unique to 0DTE in kind — the same delta-neutral hedging logic applies to every listed option. What's unique to 0DTE is the speed and concentration: the entire gamma lifecycle of a contract, from negligible to extreme back to zero, happens inside a single trading day instead of unfolding gradually over weeks.
Compressed Time Horizon, Compressed Price Effects
In a normal, longer-dated options structure, gamma-driven hedging pressure builds and fades gradually — open interest shifts over days, expirations are staggered across weeks and months, and no single day's flow dominates the picture. Levels derived from that structure (a Call Wall, a Put Wall, a Gamma Flip) tend to be relatively stable session to session.
On a 0DTE-heavy day, a meaningful fraction of the day's total gamma belongs to contracts that cease to exist at the closing bell. That means the structural picture can shift materially within the session — not just from one day to the next — as the 0DTE chain's gamma balloons near the money in the final hours and then vanishes entirely at expiry. This is a large part of why 0DTE-heavy names and indices are associated with sharper intraday reversals around scheduled events — FOMC decisions, CPI prints, monthly and quarterly expirations — where a large volume of same-day contracts all reprice at once.
What This Means for Reading GEX Levels on 0DTE-Heavy Days
The practical takeaway for anyone using options-derived context, including the GEX Levels Indicator: on 0DTE-heavy underlyings (SPX, SPY, QQQ, and a growing list of single names), be aware that a large share of the day's positioning can turn over completely by the close. A level that looks solid at 10am may reflect open interest that's actively decaying in relevance as the session progresses.
This is not a reason to distrust the data — it's a reason to treat any options-derived level as a snapshot of current structure, not a fixed line. The GEX Levels Indicator does not attempt to predict how a given session's 0DTE flow will resolve, does not produce buy or sell signals, and does not promise any outcome tied to proximity to a level. It shows you where the option-derived structure currently sits. What that structure does by the close, especially on a 0DTE-heavy day, is not something any indicator can guarantee.
Where to Go Next
If the mechanics here are new, the GEX primer covers the six level types the Indicator displays, and how dealers actually hedge gamma exposure walks through the delta-neutral hedging mechanics in more depth, with the same kind of illustrative numbers used above.
Risk disclosure. GEX Levels is operated by Marc Lalanne, entrepreneur individuel, French law. Nothing in this article is investment advice, a trading recommendation, or a guarantee of financial result. All figures above are illustrative, not live market data. Options trading involves substantial risk of loss, and 0DTE contracts in particular can experience rapid, total loss of premium. Past market behavior does not predict future results.