A measurement of a company's issued shares that are currently shorted, expressed as the number of days required to close out all of the short positions. For example, if a company has average daily volume of 1 million shares and 2 million shares are currently short sold, the shares have a cover rate of 2 days (2M/1M).

If a stock's price begins to rise significantly, investors who have short sold the stock will quickly begin to close out their positions (by purchasing shares off the open market), creating buying pressure for the stock and driving the price up even more. If a previously lagging stock turns very bullish, the buying action of short sellers can result in extra upward momentum and increased losses for short sellers who are slow to close out their positions. The longer the days to cover, the more pronounced this effect can be.