&gt; Stocks can and have fallen more than 15% in this window.<p>Possible, but not common or likely. The shares are granted at the end of one trading day (which will be the close of that day if that&#x27;s lower than at the beginning of the period) and are available for sell the next trading day. e.g. my last ESPP grant was on a Friday and I sold my shares at the open on the following Monday.<p>So for someone to <i>lose</i> money through the ESPP the stock a) would need to be lower at the end of the period then the beginning and b) drop 15% at the open. Let&#x27;s say such a move happens once a year to the average stock, there are about 250 trading days in a year so you have a 0.4% chance of that happening. (realistically it&#x27;s probably even lower than that since drastic moves like opening down 15% are much more likely to occur following an earnings announcement than on an average day and ESPP grants and earnings aren&#x27;t aligned)