The Options Clearing Corporation has a standing rule called “exercise by exception”: at expiration, any option that is $0.01 or more in-the-money is automatically exercised, whether or not you intended it. Forgetting to close a winning 0DTE option doesn't make it vanish — it makes it settle.

What that does to a long call

Say you're long a SPY 741 call and SPY closes at 741.60. It's ITM, so it auto-exercises: you buy 100 shares at $741, roughly $74,100 of stock, delivered into your account. If you were trading a $150 premium, you did not plan to suddenly own $74k of SPY. A long put works in reverse — you'd sell 100 shares you may not have, creating a short position.

In-the-money at the bell doesn't mean “cashed out.” It means “converted into stock” — and the bill lands whether you were watching or not.

How to avoid the surprise

The clean fix is to sell to close before expiration. Closing the option realizes your gain in cash and leaves you with no shares, no exercise, no settlement. If you genuinely can't cover the resulting position, see what your broker does when an option expires ITM and you don't have the cash — it's not pretty. And remember you can never be assigned on a long option; auto-exercise, not assignment, is the thing to manage. With NoVo you close an ITM same-day position in one click before the bell, so an auto-exercise never happens by accident — the exit is effortless, but the call is yours to make.