Days to cover (short interest ratio)

Days to cover, also called the short interest ratio, is a stock's short interest divided by its average daily trading volume. It estimates how many trading days it would take for all short sellers to buy back their shares if they accounted for all of the normal daily volume.

How it works

Days to cover = shares sold short / average daily volume

The average is usually taken over a recent window, such as 30 days. Because short interest is reported only twice a month, days to cover updates on the same schedule, though it shifts with volume in between.

The ratio is a simplification: short sellers would never be the only buyers, and volume itself often surges during a squeeze, shrinking the real time needed to cover.

Why it matters for traders

Days to cover measures how crowded the exit is. A stock with 20% of its float sold short but heavy daily volume may have a days to cover of only 2, so shorts can get out quickly. A stock with the same short interest but thin trading could have a ratio of 10 or more, meaning shorts may have to bid the price up sharply to cover.

That is why high days to cover is one of the classic ingredients traders look for in short squeeze candidates, often alongside a high borrow fee and a near-term catalyst. A low ratio does not mean a stock cannot squeeze, but the pressure is usually less intense.

Example

Contoso Robotics (CTSO) has 9 million shares sold short. Over the past 30 days it has averaged 900,000 shares traded per day.

Days to cover = 9,000,000 / 900,000 = 10 days

If CTSO announces a surprise contract win and volume jumps to 4.5 million shares that day, the same short position represents only 2 days of that volume, which is one reason squeezes can unwind quickly once volume arrives.

FAQ

What is a high days to cover?

Readings above about 5 to 10 days are generally considered elevated, though it depends on the stock's liquidity and history.

Is days to cover the same as short interest?

No. Short interest is the number of shares sold short. Days to cover scales that number by trading volume to show how hard it would be to unwind.