The number of shares sold short and not yet covered, usually expressed as a percentage of float.
Short interest is reported twice a month for US stocks. It tells you how many traders are betting against a company. Days-to-cover divides short interest by average daily volume to estimate how long shorts would need to buy back.
High short interest is not a buy signal or a sell signal by itself. It does mean any sharp rally forces buying from shorts, which is the mechanism of a short-squeeze.
Example: 12 million shares are short on a float of 40 million: 30% short interest. With average volume of 3 million shares, days-to-cover is 4.
Original diagrams for the ideas on this page. Illustrative, not real market data.
Bollinger bands: squeeze and expansion. The middle line is a 20-day average and the outer bands sit a set number of standard deviations away, so they measure how far price has recently been straying. When moves are small the bands pinch together; when moves grow they spread apart.
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