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Key Takeaways
- Short interest counts reported open short positions at the designated settlement date.
- FINRA collects customer and proprietary short-position reports twice each month.
- Divide shares short by public float to calculate short interest as a percentage of float.
- Divide shares short by average daily volume to calculate days to cover.
- The example’s 12 million shares short equal 15% of float and 3.0 average-volume days.
What is short interest?
Short interest is the number of shares reported as open short positions in a security at a designated settlement date. FINRA collects customer and proprietary position reports twice each month, using mid-month and month-end settlement dates. Traders scale the count by public float and by average daily volume to compare short exposure across stocks and over time.
A stock short remains an open position until it is closed or otherwise offset. Delivering borrowed shares for the initial short sale completes that sale’s delivery obligation; it does not close the short position.
Short interest percent of float and days to cover
The example has 12 million shares short, an 80 million-share public float and four million shares of average daily volume over 20 sessions.
Short interest as a percentage of float is 12 million / 80 million × 100 = 15%. Days to cover is 12 million / four million = 3.0 average-volume days.
The first ratio scales the position against available float. The second scales it against trading activity. Keep the same float definition and volume window when comparing names or successive observations.
Formula
Short interest percent of float = reported shares short / tradable public float × 100; days to cover = reported shares short / average daily share volume- Pick one float source; providers estimate float differently and update it after corporate actions.
- Average daily volume changes with the lookback window, 20 sessions in the example.
Worked Example
XYZ reports 12 million shares short. Use an 80 million-share public float and four million shares of average daily volume over a 20-session window.
- Reported short interest: 12,000,000 shares
- Estimated float: 80,000,000 shares
- Short interest percent of float: 15%
- Average daily volume: 4,000,000 shares
- Days to cover: 3.0
Twelve million shares short divided by 80 million float shares equals 15%. Dividing the same short position by four million average daily shares gives 3.0 days to cover. Read the first ratio as position concentration and the second as position size relative to trading volume.
How to read changes in short interest
Compare reported short positions with price action over the corresponding period. A rising share count means more reported short exposure; a falling count means less. Changes in float or average volume also change the normalized ratios.
Borrow fees and available loan inventory describe financing conditions. Short-sale volume describes transaction activity, while settlement-failure data describes delivery obligations. Combine positioning with the price levels and catalyst you are trading, then check the contract activity around the setup in options flow.
Limitations of short interest
- Check the settlement date. FINRA counts positions twice a month and shorts change every session, so read each report as of its mid-month or month-end date and track borrow fees and price action since then.
- Fix the float source and volume window. Float estimates differ by provider and change after corporate actions, and days to cover moves with the lookback, so compare names on one basis.
- Read 3.0 days to cover as a floor. Shorts who buy back share the tape with every other buyer, so covering 12 million shares takes longer than 3.0 days at 4 million a day, and longer still if volume dries up.
- Read intent from context. Hedges and directional bets look the same in the total, so check convertible issuance, merger arbitrage and options activity before you call it a bearish crowd.
- Pair the count with borrow fees. Short-sale volume shows trading activity, borrow fees show what it costs to stay short, settlement-failure data shows delivery problems, and only short interest counts the open positions.
Bottom line
Short interest shows how many shares are sold short and still open at each reporting date. Scale it by float and average volume with consistent definitions, track the change between reports, and read it with borrow conditions, price action and the catalyst to decide whether heavy short positioning sets up a squeeze or confirms the bearish case.
Clear answers
Frequently Asked Questions
Sources and Further Reading
How entries are sourced, calculated and updated: editorial methodology.