Expiration choice trades decay against risk. Time decay accelerates as expiration approaches, but so does gamma, the speed at which a position's directional exposure changes. The 30-45 days-to-expiration window is the classic compromise for premium selling: meaningful decay, gamma still manageable, and time to adjust when a strike is tested.
Theta, the daily decay collected by a short premium position, grows as expiration approaches; on that measure alone, the shortest expiration pays fastest. But gamma grows even faster into expiration: near-dated short strikes flip from safe to breached on ordinary daily moves, leaving no time to react. Entering around 30-45 DTE and exiting well before expiration harvests the fat middle of the decay curve while gamma is still shallow. The matching exit convention, closing at a fixed fraction of the credit or at 21 DTE, exists for the same reason: the final weeks hold the least remaining decay and the most gamma.
Options Scanner scores every listed expiration rather than assuming one, because chains differ. The score blends:
A score built on those measures alone will happily land on a weekly expiration with beautiful math and no market: single-digit open interest and dollar-wide quotes. Liquidity therefore steers the final selection; the discipline prefers the top-scoring expiration whose strikes clear open-interest, volume, and quote-width floors, and records an honest rejection when none do. A great expiry score on an untradeable chain is a trap, and treating it as such in the rules, rather than in the trader's memory, is what makes the discipline repeatable.
That window balances two curves that pull in opposite directions: theta decay accelerates as expiration approaches, and so does gamma, the sensitivity that makes a position swing hard near its strikes. Around 30 to 45 days a structure still collects meaningful decay without yet taking on expiration-week gamma, which is why so many published rule sets land there.
Per calendar day, yes: an at-the-money option's time value erodes roughly with the square root of remaining time, so the final week burns premium fastest. The same acceleration applies to risk, since short-dated options gain and lose value violently around the strike.
The chain starts pricing the scheduled jump, inflating implied volatility for every expiration that contains the event. A decay-focused position would then be holding a known binary event it was not designed for, which is why expiry-selection rules commonly either skip past the event or exclude the name until it has reported.