If you short a stock, you must recognize a gain when it falls so much that it is deemed "worthless". How is that defined? I am thinking of a long-term short in VXX, which is an exchange-traded note that tracks a long VIX futures position. VXX has fallen 48% a year over the last 5 years, but it is periodically reverse split when the share price falls to a low level, and it continues to trade very actively. According to the VXX prospectus, it was issued on Feb 3 2009 and will mature on Jan 30 2019. So could you delay realizing the gain until 2019 if short? I do realize the VXX is very volatile and that shorting it is risky.