Biotech IR Blog by Our CEO and Founder, Laurence Watts.
December 10, 2025
What is the Typical Short Interest in a U.S. Public Biotech?
Biotech CEOs and CFOs tend to have a visceral reaction when they hear about the short interest in their stock. The purpose of this blog, however, is to demonstrate that not all short interest positions are equal, and to provide context for typically how shorted the average public biotech actually is.
Technically, shorting a stock means borrowing shares from a third party and selling them immediately, with the intent of buying them back at a lower price before the shares need to be returned – thus making a profit. In other words, “shorting” is betting on a biotech’s stock price falling.
However, in addition to bearish, fundamentally driven shorts, there is typically a minimum short interest driven by technical factors, with shorts being used, for example, by market makers hedging options, convertible arbitrage funds hedging bonds, or ETF basket traders balancing exposures. These structural activities create a steady short interest even when a company’s fundamentals are strong.
An interesting data point is that every one of the 195 public biotechs we looked at for this blog had a non-zero short interest. The point being – biotechs are always going to have a short interest, it isn’t necessarily nefarious.
Where do we get short information from?
While long positions are disclosed via 13F reports, knowing who has taken a short position in a company’s stock is more difficult to ascertain.
This is because the information we have on short positions comes not from funds, but from the brokers they utilize in running their portfolios. FINRA Rule 4560 mandates that every member (i.e. every brokerage) must report total short positions (both customer and proprietary accounts) in all equities, in both the middle of and at the end of each month. FINRA then provides the data to exchanges like Nasdaq and the NYSE for public disclosure. Importantly, because only the total short position is revealed, there is no way to know precisely which fund, broker or individual has actually shorted a stock.
So, what’s a typical short position in a U.S. public biotech?
We decided to look at short positions across “small”, “medium” and “large” Nasdaq-listed biotechs.
- We took the 247 constituents of the Nasdaq Biotechnology Index (NBI) as of November 24, 2025.
- Since the floor for NBI inclusion is a $200 million market cap, we excluded biotechs with lower market caps from our analysis.
- At the other end of the spectrum, we decided to exclude any biotech with a market cap of more than $10 billion.
- This left us with 76 “small” biotechs, 68 “medium” biotechs, and 51 “large” biotechs, as shown in the table below.
| Description | Market Cap Range | Number of Biotechs |
| < $200M | < $200M | 19 |
| Small Biotechs | $200M – $1B | 76 |
| Medium Biotechs | $1B – $2.5B | 68 |
| Large Biotechs | $2.5 – $10B | 51 |
| > $10B | > $10B | 33 |
Source: Nasdaq, New Street Investor Relations
The metric we were interested in looking at was Days to Cover. Days to Cover is the best metric for assessing short positions because it blends short interest with liquidity. Instead of just showing how many shares are shorted, it shows how hard it would be for shorts to exit, by dividing the absolute short interest by a stock’s average daily trading volume. High Days to Cover signals a crowded trade and a greater squeeze risk.
We also chose two time points at which to measure average short interest – 12/31/24 and 6/30/25 – to see if there was any meaningful movement in the first half of 2025.
“Small” Biotechs ($200M – $1B), n=76
| Date | December 31, 2024 | June 30, 2025 |
| Average Short Interest (Days to Cover) | 8.0 | 8.1 |
Source: Nasdaq, New Street Investor Relations
- The average (mean) short interest in a “small” biotech was 8.0 Days to Cover at the end of 2024 and was almost unchanged at 8.1 days to cover at mid-2025.
Most shorted – June 30, 2025
| Biotech | Ticker | Short Interest (Days to Cover) |
| Design Therapeutics | DSGN | 41.3 |
| Anavex Life Sciences | AVXL | 22.0 |
| Enanta Pharmaceuticals | ENTA | 17.4 |
| Theravance Biopharma | TBPH | 15.1 |
| Erasca Inc. | ERAS | 14.9 |
Source: Nasdaq, New Street Investor Relations
- Within “small” biotechs, Design Therapeutics was the most shorted stock on June 30, 2025, at 41.3 Days to Cover, with Anavex Life Sciences, Enanta, Theravance Biopharma and Erasca rounding out the top five.
Least shorted – June 30, 2025
| Biotech | Ticker | Short Interest (Days to Cover) |
| Lyell Immunopharma | LYEL | 1.1 |
| Prothena Corp. | PRTA | 1.7 |
| Altimmune Inc. | ALT | 1.9 |
| Amarin Corp. | AMRN | 1.9 |
| Sutro Biopharma | STRO | 2.0 |
Source: Nasdaq, New Street Investor Relations
- At the other end of the spectrum, Lyell Immunopharma was the least shorted “small” biotech at 1.1 Days to Cover, with Prothena, Altimmune, Amarin and Sutro not far behind.
Medium Biotech ($1B – $2.5B), n=68
| Date | December 31, 2024 | June 30, 2025 |
| Average Short Interest (Days to Cover) | 9.4 | 8.7 |
Source: Nasdaq, New Street Investor Relations
- The average (mean) short interest in a “medium” biotech was 9.4 Days to Cover at the end of 2024 and was not materially different at 8.7 Days to Cover at mid-2025.
Most shorted – June 30, 2025
| Biotech | Ticker | Short Interest (Days to Cover) |
| Immunocore Holdings | IMCR | 22.3 |
| Anaptysbio, Inc. | ANAB | 19.6 |
| Rapport Therapeutics | RAPP | 19.4 |
| Monte Rosa Therapeutics | GLUE | 18.8 |
| Nurix Therapeutics | NRIX | 18.4 |
Source: Nasdaq, New Street Investor Relations
- Within “medium” biotechs, Immunocore Holdings was the most shorted stock on June 30, 2025, at 22.3 Days to Cover, with Anaptysbio, Rapport Therapeutics, Monte Rosa Therapeutics and Nurix Therapeutics completing the top five.
Least shorted – June 30, 2025
| Biotech | Ticker | Short Interest (Days to Cover) |
| Curevac | CVAC | 1.0 |
| Tyra Biosciences | TYRA | 1.2 |
| Sarepta Therapeutics | SRPT | 1.2 |
| Kiniska Pharma | KNSA | 1.4 |
| Urogen Pharma | URGN | 1.7 |
Source: Nasdaq, New Street Investor Relations
- Turning to the least shorted “medium” biotechs at mid-2025, Curevac was the least shorted at 1.0 Days to Cover, followed by Tyra, Sarepta, Kiniska and Urogen.
Large Biotech ($2.5B – $10B), n=51
| Date | December 31, 2024 | June 30, 2025 |
| Average Short Interest (Days to Cover) | 8.8 | 7.2 |
Source: Nasdaq, New Street Investor Relations
- Lastly, the average (mean) short interest in a “large” biotech was 8.8 Days to Cover at the end of 2024 and 7.2 Days to Cover by mid-2025.
Most shorted – June 30, 2025
| Biotech | Ticker | Short Interest (Days to Cover) |
| Immunovant | IMVT | 15.0 |
| Crinetics Pharma | CRNX | 14.9 |
| Apellis Pharma | APLS | 14.0 |
| Tarsus Pharma | TARS | 13.7 |
| Mirum Pharma Inc. | MIRM | 13.7 |
Source: Nasdaq, New Street Investor Relations
- Within “large” biotechs, Immunovant was the most shorted stock on June 30, 2025, at 15.0 Days to Cover, followed by Crinetics, Apellis, Tarsus and Mirum.
Least shorted – June 30, 2025
| Biotech | Ticker | Short Interest (Days to Cover) |
| Halozyme Therapeutics | HALO | 2.4 |
| Indivior Global Pharma | INDV | 2.6 |
| Amicus Therapeutics | FOLD | 3.2 |
| Adaptive Biotech | ADPT | 3.2 |
| Centessa Pharma | CNTA | 3.3 |
Source: Nasdaq, New Street Investor Relations
- Turning to the least shorted “large” biotechs at mid-2025, Halozyme was the least shorted at 2.4 Days to Cover, followed by Indivior Global Pharma, Amicus, Adaptive and Centessa.
Why might a fund take a short position in a biotech?
When looking at some of the “small”, “medium” and “large” biotechs above with high short positions, one can theorize reasons for why funds might want to short the stock. More often than not, short positions increased ahead of clinical data readouts (with shorting funds likely hypothesizing that the results would be negative or else demonstrate an unfavorable safety profile).
Conclusions
- First, we did not find a material difference in average short interest between 12/31/24 and 6/30/25 across all three categories of biotech (small, medium and large).
- Second, for all the biotechs we looked at, the average short interest was approximately 8 Days to Cover.