Deciding To Carry A Position Overnight

During the trading day, if news breaks against a position, you can react — trim it, hedge it, cut it entirely, all within minutes. Overnight, none of that is available: a position held through the close is a position you have committed to holding through whatever happens between now and the open, with your stop-loss order sitting there unable to fill until the market reopens, potentially far below where it was set. Carrying a position overnight is a real decision, distinct from the decision to hold it during the day, and it deserves to be made on purpose rather than by default.

What changes the calculation after the close

The list of things that can move a stock overnight and that you cannot react to as they happen is long and specific to the position: earnings releases, scheduled after the market close or before the open; a competitor's earnings that reveal industry-wide trends; regulatory or legal news; overseas markets trading while the US is closed, especially relevant for anything with meaningful non-US revenue; and, for a short position, a buy-in or borrow recall notice that can only be resolved once trading resumes. None of these are exotic — earnings season alone means a large share of a typical long-short book has at least one position facing a real overnight catalyst on any given week.

The practical question is not "is there any overnight risk" — there always is some — but "is the position sized for the range of outcomes that could show up at tomorrow's open, given that I cannot exit at my intended stop level before then."

Worked example

You hold $2m of a stock ahead of its earnings release tonight after the close. Your normal risk-budget sizing assumed an intraday stop at 8% away, giving a maximum loss of $160,000 if the stop worked as designed.

Historical earnings moves for this name average an 11% overnight gap, with the largest move in the last eight quarters at 19%. The stop cannot function overnight — there is no market to fill it in between the close tonight and the open tomorrow. The real distribution of outcomes you are actually exposed to, by holding through the print, is not "8% stop, $160k max loss" but something closer to "could open down 19%, a $380,000 loss, with no ability to have exited earlier."

Given that, the position as sized for intraday risk is not the position you would choose to hold through an 11-19% overnight range. The decision is either to trim ahead of the print to a size where a 19% gap is inside the risk budget (roughly $840,000 at the same $160k budget), or to hold the full size deliberately because the thesis specifically depends on the earnings outcome — but either way, it is a decision made with the wider overnight range in view, not the intraday stop distance carried forward by default.

The default answer should not be "hold"

Because trimming ahead of a known catalyst has a real cost — you may miss the upside if the news is good, and there is a transaction cost to reducing and rebuilding — it is tempting to treat "still holding" as the neutral, no-decision default. It is not neutral; it is a decision to accept the wider overnight range, and it should be made as explicitly as the decision to put the trade on in the first place.