0DTE, Events and the Short-Dated Edge

Same-day options: a position on the path

A zero-days-to-expiry contract is the extreme case of everything O11 and O12 established. Gamma peaks near expiry and near the money, theta follows it, and vega collapses toward nothing — so a same-day at-the-money option is almost pure convexity, with no time for the other Greeks to matter. That changes what the position *is*. A thirty-day call can be right about direction and still lose if it is right too slowly; a same-day call cannot be right slowly at all, because there is no later. On a $50 stock with a $0.95 at-the-money contract, delta 0.53 and gamma 0.24, a one-dollar move is worth $53 of delta and $12 of gamma per contract — and the gamma term grows with the square of the move, so a two-dollar move is worth $154 per contract rather than $106, and a flat close is worth the whole premium. Ten contracts therefore need roughly a 2% move to recover two-thirds of their cost and a 4% move to more than double it. The instrument is not a lottery ticket in the sense of being directionally hopeful; it is a precise bet that the day’s *range* will be large, and its cost is the entire premium every time the day is quiet. The scale of the market is the reason this is no longer a curiosity. Cboe reported SPX same-day options setting an average daily volume record of 2.3 million contracts in 2025 — 59% of total SPX volume — which means the flow is institutional, systematic and frequently *short* the same contracts a retail trader is buying. The seller of a same-day option is being paid an enormous theta to accept an enormous gamma, and that seller is usually hedged elsewhere, which is why the volume itself changes the market’s intraday behaviour: hedging flow from short-dated positions is a real component of the tape and of the closing prints. Two consequences for a learner. The first is that “everyone is buying 0DTE calls” is not evidence of anything except that the option is available and cheap in dollars. The second is that the position is a *path* instrument: the same closing price can leave a same-day call worthless or valuable depending on whether the stock got there early and sat still or spiked into the close, because the gamma the buyer paid for was only realised if the stock moved enough while there was time left to be exercised. That is why the discipline for these contracts is to decide the exit in advance — the profit target, the time stop and the maximum number of contracts — and to treat the close as a deadline rather than a horizon. Ten contracts, one session — Cost: ten at $0.95: $950 of premium, all of it extrinsic ← · Stock at $51.00 at the close: About $650 of profit — roughly two-thirds of the cost recovered · Stock at $52.00 at the close: About $1,540 — the gamma term is what turns a 4% move into a 162% return · Stock at $50.00 at the close: The entire $950 is gone — at the money at expiry is worth nothing · What is actually being bought: The size of the day’s range, not its direction A delta-only estimate says the position breaks even on a $1.79 move, but gamma makes the real requirement smaller and makes the payoff nonlinear — which is the entire reason the contract is bought.

Event risk: the premium charged before and drained after

An earnings report is a same-day problem at a longer scale. The chain prices the event as an **implied move** — the one-sigma band from O8, usually quoted at the at-the-money strike as the market’s estimate of the report’s likely size — and the front-month implied volatility rises into the print and collapses after it, because the uncertainty the contract was pricing has been replaced by a fact. That collapse is the **volatility crush**, and it is the single most common way a correct view loses money: buy a call before a report, watch the company beat estimates and guide higher, watch the stock open two percent up — and watch the call lose value, because the implied move was six percent and the realised move was two, and the excess premium that was paid for the hypothetical six drains out in the first minutes of trading. Vega is the Greek that explains it, and O12 priced it: a five-point volatility fall across three contracts cost $165, about seventeen sessions of theta, in a single session. The correct response is not to avoid events but to hold the view in the right structure. If the thesis is about the business over a year, own a longer-dated contract whose vega will survive the print and whose expiry does not force the decision. If the thesis is about the report itself, compare the implied move with your own estimate of the move before paying for it, and be explicit that you are buying the *size* — a straddle bought before a print needs the realised move to exceed the implied one, and the historical distribution of that comparison is the only evidence worth having. The third structure is to sell the event premium rather than buy it, which is the same trade from the other side and carries the same requirement in reverse: a short-dated condor or iron fly collects the rich event premium and is destroyed by a large realised move, so it has to be sized from the tail exactly as O17 described. One more piece of short-dated mechanics deserves a place because it is widely repeated and often wrong. The claim is that dealer hedging flows — market makers who are short gamma and must buy as the stock rises and sell as it falls — can *cause* a move, and that this is why certain names squeeze. The verifiable part is that such flows exist and that they amplify moves: a dealer short gamma has to trade in the direction of the market to stay hedged, which adds demand to a rise and supply to a fall. The unverifiable part is the attribution — how much of any given squeeze was hedging flow versus genuine buying versus a short base, and in what order. The honest position is to treat the mechanism as real and the causal claims as unproven in any individual case, which matters because the flow is one input among several and the positions that would confirm it are not public. • An event premium is charged into the front-month implied volatility and drained after the print — the volatility crush. • A correct direction can lose if the realised move is smaller than the implied move that was paid for. • Implied move matters more than direction: compare it with your own estimate before buying the event. • Dealer hedging flows are real and amplify moves; attributing a specific squeeze to them is usually unproven. • Short-dated positions are sized from the tail, with the exit — target, time stop and maximum contracts — decided before entry. The failure of a short-dated position is rarely a bad thesis; it is a position sized as if the premium were the risk when the gamma is. Ten same-day contracts cost $950 and can lose all of it in five quiet hours, and the same trader who would never risk $950 on a chart pattern will happily risk it on a coin-flip session because the number of contracts felt small.

Sources

• Gamma, pin risk and near-expiry behaviour in short-dated optionsNatenberg, “Option Volatility and Pricing”
• SPX 0DTE average daily volume of 2.3 million contracts, 59% of total SPX volume, full-year 2025Cboe Global Markets, 2025 volume report
• The earnings premium: implied versus realised moves and the post-report volatility collapseCboe Options Institute research on earnings volatility