I just started selling the cash secured puts. I was under the impression that all options unless in the money expire worthless on the expiration day but apparently that's not the case. I had sold a put for $3.40 and bought it back for $2.40 before close but it's last price at the market close on Friday was $4.25, so had I held the option thinking that it would expire worthless, I would have lost $85.00. It was a TSLA put for $635, stock closed at $675 so I am wondering how come it wasn't worthless? Also had I not bought it back I know that at the close my account would show a loss of $85 but would it later show a profit of full $340 premium on next Saturday when actually that option from last week is delisted?