Expiry selection | The Greeks Desk

Strike selection sets where a credit spread sits relative to the underlying. Expiry selection sets how much time the trade has to play out, and it comes with its own tradeoff: shorter-dated options decay faster, but give the trade less room to be wrong.

Theta, covered earlier in this curriculum, describes how an option loses value as time passes. That decay isn't constant across a contract's life; it accelerates as expiry approaches. A short-dated spread benefits from that faster decay working in the seller's favour, but it also means the trade has fewer days for the underlying to recover if it moves the wrong way early on.

A simple example. A spread expiring in one to three days decays quickly day to day, which is part of why this style of trading on NDX and SPX exists. But if the underlying makes a sharp move against the position on day one, there's very little time left for it to reverse. A spread expiring in several weeks decays more slowly on any single day, but gives the underlying far more time to move away from the short strike and still come back before expiry.

Faster decay, less room to be wrong

Short-dated trades can see their risk profile change quickly. Because there's so little time value left, the option's price and delta can shift fast on even a modest move in the underlying, which means a position that looked comfortably out of the money can look very different within hours, not days. That speed is exactly what attracts some traders to short-dated index trading, and exactly what makes it demanding to manage.

Slower decay, more room to adjust

Longer-dated trades give up some of that speed. The daily decay is smaller, so the trade takes longer to reach its full profit potential. In exchange, the position has more time to absorb a move against it, and more time for the trader to consider closing early or adjusting before expiry, a topic covered elsewhere on this site. Neither of these is simply "better." They suit different amounts of active attention and different tolerances for how quickly a position's risk can change.

A genuine tradeoff, not a right answer

It can be tempting to think shorter is always better because it decays fastest, but that decay comes paired with less margin for error and a faster-moving position. Choosing an expiry means weighing that speed against how much time you actually have, and want, to watch and manage the trade.

Rule of thumb. Match the expiry to how much moment-to-moment risk you're genuinely comfortable actively managing, not just to whichever decays fastest on paper. A trade you can't watch closely enough to manage well isn't a good fit just because the theta looks attractive.

What this doesn't mean

It doesn't mean short-dated trades are reckless or long-dated trades are always safer. Each carries a different shape of risk, not simply more or less of it.
It doesn't mean faster decay equals a better trade. Decay is only one side of the tradeoff; room to be wrong is the other.
It doesn't mean any particular expiry suits every trader or every market condition. This is a framework for thinking it through, not a fixed rule.