Short Interest and Days to Cover

Short interest is the total number of shares of a stock currently sold short and not yet covered — reported by exchanges and FINRA roughly twice a month in the US. It's often expressed as a percentage of shares outstanding or, more usefully, as a percentage of the free float, since float is what actually determines how crowded a trade is relative to the shares available to trade.

Days to cover (also called the short interest ratio) takes that raw short interest number and divides it by the stock's average daily trading volume, answering a more concrete question: if every short seller decided to buy back their position today, and no one else traded, how many trading days would it take to unwind the whole thing? A high days-to-cover number is one of the standard, if crude, proxies for squeeze risk — it says the exit door is small relative to the crowd trying to use it, not that a squeeze will happen.

Worked example

$$\text{Days to cover} = \frac{\text{Shares sold short}}{\text{Average daily trading volume}}$$

Metric	Value
Shares sold short	40 million
Shares outstanding	200 million
Short interest as % of shares outstanding	20%
Average daily trading volume	4 million shares
Days to cover	40m / 4m = 10 days

A days-to-cover reading of 10 is high — most liquid large caps sit under 2 or 3. It means the entire short position is ten times the stock's typical single-day volume, so any sudden wave of buying (a positive earnings surprise, a short-seller margin call, a buyout rumor) has a much larger pool of forced buyers to draw from relative to the market's normal capacity to absorb orders, which is exactly the setup that produces a short squeeze.

Days to cover is a snapshot, not a live number — short interest is only reported roughly twice a month, so between reports the ratio can drift meaningfully as volume and the actual short position both change, and a squeeze can begin well before the next official reading confirms how crowded the trade had become.