Short Interest
Definition
Short interest is the total number of a stock's shares currently sold short, expressed as a percentage of the float — it measures the collective bearish bet against a stock, and when short interest is high (above 20%), it signals both that many traders expect the stock to fall and that the setup conditions for a short squeeze are developing.
Example
“The stock had 38% short interest and a 5-day short ratio — meaning at current volume it would take 5 days for all the shorts to cover. When positive news hit, there wasn't enough supply to absorb the forced buying and the stock tripled.”
Detailed Explanation
Short interest data is publicly reported twice per month by FINRA and available on most financial data platforms. The two most useful metrics derived from it are short interest as a percentage of float (how crowded the short trade is) and the short interest ratio, also called days-to-cover (total short shares divided by average daily volume — how many trading days it would take for all shorts to cover at current volume). A short interest ratio above 5-7 is considered high and signals that any forced buying event could cause a significant and rapid squeeze because shorts can't exit quickly.
High short interest cuts both ways. On one hand, it confirms that sophisticated traders are bearish — short sellers typically do fundamental research and their collective judgment about the company may be correct. A highly shorted stock may be shorted for very good reasons (questionable accounting, declining business, massive debt). On the other hand, high short interest is the fuel that powers short squeezes when positive catalysts arrive. The more shorts there are, the more forced buying happens when the stock starts rising, which is why high-short-interest stocks can make explosive multi-day moves on positive catalysts even when the fundamental thesis for shorting remains intact.
For day traders, short interest is most useful as context rather than a standalone trade signal. A stock with 30% short interest breaking out on news has a tailwind beyond just technical buyers — short sellers covering adds purchasing power to the move. A stock with 30% short interest that is rolling over after a failed rally has a more bearish setup than the same chart pattern in a stock with 2% short interest, because there's less short covering demand to cushion declines. Always check short interest when evaluating potential squeeze candidates or when assessing the risk of a short trade you're considering.