Prothena (PRTA) Short Interest Ratio & Short Volume $9.59 -0.17 (-1.74%) Closing price 05/18/2026 04:00 PM EasternExtended Trading$9.85 +0.26 (+2.66%) As of 05/18/2026 04:10 PM Eastern Extended trading is trading that happens on electronic markets outside of regular trading hours. This is a fair market value extended hours price provided by Massive. Learn more. Add Compare Share Share Short Interest Stock AnalysisAnalyst ForecastsChartCompetitorsEarningsFDA EventsFinancialsHeadlinesInsider TradesOptions ChainOwnershipSEC FilingsShort InterestTrendsBuy This Stock Prothena Short Interest OverviewAs of April 30, 2026, Prothena (PRTA) had a short interest of 6.87 million shares sold short, representing 14.65% of the public float. This marks a -2.90% decrease in short interest since the prior report. The short interest ratio (days to cover) is 18.3, meaning it would take 18.3 days of the average trading volume of 473,597 shares to cover all short positions.Current Short Interest6,871,465 sharesPrevious Short Interest7,076,832 sharesChange Vs. Previous Month-2.90%Dollar Volume Sold Short$76.00 millionShort Interest Ratio18.3 Days to CoverLast Record DateApril 30, 2026Outstanding Shares52,350,000 sharesShort Percent of Float14.65%Today's Trading Volume650,972 sharesAverage Trading Volume473,597 sharesToday's Volume Vs. Average137% Short Selling Prothena? Sign up to receive the latest short interest report for Prothena and its competitors with MarketBeat's FREE newsletter. Email Address Get Report View SMS TermsSMS is currently available in Australia, Belgium, Canada, France, Germany, Ireland, Italy, New Zealand, the Netherlands, Singapore, South Africa, Spain, Switzerland, the United Kingdom, and the United States. 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Skip Charts & View Short Interest HistoryShort Interest ChartDays to Cover ChartShort Percent of Float ChartPRTA Short Interest Over TimePRTA Days to Cover Over TimePRTA Percentage of Float Shorted Over Time Prothena Tesla Short Interest History & Recent Changes ExportReport DateTotal Shares Sold ShortDollar Volume Sold ShortChange from Previous ReportPercentage of Float ShortedDays to CoverPrice on Report Date 4/30/20266,871,465 shares $76.00 million -2.9%14.6%18.33 $11.06 4/15/20267,076,832 shares $76.57 million +0.9%14.7%15.33 $10.82 3/31/20267,016,080 shares $68.20 million -0.4%14.5%12.32 $9.72 3/13/20267,044,790 shares $64.88 million +2.8%14.5%11.2 $9.21 2/27/20266,854,767 shares $59.43 million -3.2%14.1%17.22 $8.67 2/13/20267,083,043 shares $63.46 million +0.3%14.6%18.12 $8.96 1/30/20267,063,694 shares $62.23 million -0.1%14.6%13.9 $8.81 1/15/20267,069,471 shares $65.46 million +7.4%14.6%14.42 $9.26 12/31/20256,584,532 shares $62.88 million +40.1%13.6%7.96 $9.55 12/15/20254,699,126 shares $46.85 million +1.3%9.7%6.78 $9.97 Get the Latest News and Ratings for PRTA and Related StocksEnter your email address below to receive the latest news and analysts' ratings for Prothena and its competitors with MarketBeat's FREE daily newsletter. 11/28/20254,639,338 shares $46.25 million -0.4%9.6%9.02 $9.97 11/14/20254,657,490 shares $46.25 million +12.4%9.6%7.38 $9.93 10/31/20254,144,115 shares $44.55 million +7.4%8.6%8.06 $10.75 10/15/20253,860,000 shares $41.15 million +0.3%8.9%4.4 $10.66 9/30/20253,850,000 shares $37.58 million +2.4%8.9%4.2 $9.76 9/15/20253,760,000 shares $30.68 million -7.4%8.7%3.8 $8.16 8/31/20254,060,000 shares $33.29 million -2.9%9.3%3.3 $8.20 8/15/20254,180,000 shares $34.49 million -4.4%9.6%2.7 $8.25 7/31/20254,370,000 shares $30.02 million -8.2%10.5%2.7 $6.87 7/15/20254,760,000 shares $29.61 million +9.9%11.3%2.7 $6.22 6/30/20254,330,000 shares $26.28 million -7.1%10.2%2.5 $6.07 6/15/20254,660,000 shares $23.67 million +5.7%11.0%2.9 $5.08 5/31/20254,410,000 shares $20.24 million -50.7%10.4%3.3 $4.59 5/15/20258,950,000 shares $60.14 million +20.1%21.2%8.4 $6.72 4/30/20257,450,000 shares $68.54 million -5.9%N/A9.9 $9.20 4/15/20257,920,000 shares $75.95 million -5.5%18.6%17 $9.59 3/31/20258,380,000 shares $103.74 million -4.6%19.7%18.7 $12.38 3/15/20258,780,000 shares $120.64 million -3.8%20.7%17.9 $13.74 2/28/20259,130,000 shares $144.35 million +1.1%21.5%18.2 $15.81 2/15/20259,030,000 shares $127.96 million +1.5%21.3%18 $14.17 1/31/20258,900,000 shares $126.65 million -4.8%N/A17.2 $14.23 1/15/20259,350,000 shares $124.07 million +6.6%N/A17 $13.27 12/31/20248,770,000 shares $121.46 million -0.3%N/A15.8 $13.85 12/15/20248,800,000 shares $112.55 million +9.2%N/A14.4 $12.79 11/30/20248,060,000 shares $130.65 million +2.3%N/A15.3 $16.21 11/15/20247,880,000 shares $110.40 million +4.7%N/A15.9 $14.01 10/31/20247,530,000 shares $128.01 million +10.9%N/A16.3 $17.00 10/15/20246,790,000 shares $114.89 million +28.1%N/A15.3 $16.92 9/30/20245,300,000 shares $88.67 million -7.3%N/A11.5 $16.73 9/15/20245,720,000 shares $126.47 million +2.3%N/A14.9 $22.11$30 stock to buy before Starlink goes public (WATCH NOW!) 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No credit card is required to get the ticker.Watch the free video to get the ticker today. 8/31/20245,590,000 shares $124.49 million +3.9%N/A12.8 $22.27 8/15/20245,380,000 shares $112.28 million No ChangeN/A11.4 $20.87 7/31/20245,380,000 shares $125.25 million +12.8%N/A10.7 $23.28 7/15/20244,770,000 shares $107.75 million -6.5%N/A9.1 $22.59 6/30/20245,100,000 shares $105.26 million -23.4%N/A9.7 $20.64 6/15/20246,660,000 shares $135.93 million -0.8%N/A12.2 $20.41 5/31/20246,710,000 shares $139.64 million +3.1%N/A12.6 $20.81 5/15/20246,510,000 shares $145.76 million -3.6%N/A11.9 $22.39 4/30/20246,750,000 shares $137.30 million +1.8%N/A11.1 $20.34 4/15/20246,630,000 shares $145.79 million +2.5%N/A10.1 $21.99 3/31/20246,470,000 shares $160.26 million +3.5%N/A8.1 $24.77 3/15/20246,250,000 shares $162.94 million +3.0%N/A7.6 $26.07 2/29/20246,070,000 shares $167.47 million +4.5%N/A7 $27.59 2/15/20245,810,000 shares $165.70 million +1.0%N/A6.6 $28.52 1/31/20245,750,000 shares $163.24 million -8.2%N/A6.8 $28.39 1/15/20246,260,000 shares $217.03 million +3.0%N/A7 $34.67 12/31/20236,080,000 shares $220.95 million +4.5%N/A6.8 $36.34 12/15/20235,820,000 shares $232.74 million -15.0%N/A7.6 $39.99 11/30/20236,850,000 shares $223.17 million +10.7%N/A10.1 $32.58 11/15/20236,190,000 shares $217.15 million -4.8%N/A9.6 $35.08 10/31/20236,500,000 shares $236.99 million +28.0%N/A10.6 $36.46 10/15/20235,080,000 shares $223.93 million +15.7%N/A10.4 $44.08 9/30/20234,390,000 shares $211.82 million +2.6%N/A10.7 $48.25 9/15/20234,280,000 shares $224.53 million +3.9%N/A11.2 $52.46 8/31/20234,120,000 shares $217.62 million +11.4%N/A10.6 $52.82 8/15/20233,700,000 shares $223.33 million +0.8%N/A9.4 $60.36 7/31/20233,670,000 shares $252.75 million +0.8%N/A9 $68.87 7/15/20233,640,000 shares $254.84 million +3.4%N/A8.3 $70.01 6/30/20233,520,000 shares $240.35 million -4.4%N/A7.9 $68.28 6/15/20233,680,000 shares $267.06 million +10.8%N/A7.8 $72.57 5/31/20233,320,000 shares $220.55 million +3.4%N/A7.1 $66.43 5/15/20233,210,000 shares $240.65 million -1.8%N/A6.7 $74.97 4/30/20233,270,000 shares $172.07 million No ChangeN/A6.9 $52.62 4/15/20233,270,000 shares $164.91 million -11.9%N/A7.5 $50.43 3/31/20233,710,000 shares $179.82 million +7.5%N/A8.3 $48.47 3/15/20233,450,000 shares $169.15 million +11.7%N/A6.9 $49.03 2/28/20233,090,000 shares $172.30 million +4.4%N/A5.9 $55.76 2/15/20232,960,000 shares $159.60 million +6.5%N/A5.6 $53.92 1/31/20232,780,000 shares $157.21 million -3.5%N/A5 $56.55 1/15/20232,880,000 shares $163.87 million +9.1%N/A5 $56.90 12/30/20222,640,000 shares $159.06 million +9.5%N/A4.4 $60.25 12/15/20222,410,000 shares $141.03 million +6.6%N/A2.9 $58.52 11/30/20222,260,000 shares $141.27 million +1.4%N/A2.7 $62.51 11/15/20222,230,000 shares $138.64 million -8.2%N/A2.7 $62.17 10/31/20222,430,000 shares $149.30 million -10.7%N/A3.1 $61.44 10/15/20222,720,000 shares $149.19 million -16.6%6.2%3.7 $54.85 9/30/20223,260,000 shares $197.65 million +32.5%7.4%4.8 $60.63 9/15/20222,460,000 shares $73.80 million -8.2%5.6%6.5 $30.00 8/31/20222,680,000 shares $73.89 million +2.3%6.1%7.5 $27.57 8/15/20222,620,000 shares $85.57 million -0.4%6.0%7.9 $32.66Louis Navellier: My #1 AI stock for 2026 (name & ticker inside) (Ad)Louis Navellier's Stock Grader system helped him flag Nvidia before its 82,000% run and has identified the top S&P 500 stock for 12 years running—and today, he's giving away his #1 AI stock pick for 2026, free. This company's sales are up 28% year over year, it holds over 30,000 patents in wireless and video technology, and it just earned an A-rating in his proprietary Stock Grader system that has cost him $9 million to build and maintain.Get the name and ticker of Louis Navellier's #1 AI stock free 7/31/20222,630,000 shares $81.69 million -12.9%6.0%6.9 $31.06 7/15/20223,020,000 shares $92.74 million -0.3%6.9%7.2 $30.71 6/30/20223,030,000 shares $82.26 million -8.7%6.9%7.1 $27.15 6/15/20223,320,000 shares $78.62 million -7.8%8.3%7.8 $23.68 5/31/20223,600,000 shares $98.03 million +4.4%N/A8.8 $27.23 5/15/20223,450,000 shares $90.74 million +31.2%N/A8 $26.30 4/30/20222,630,000 shares $76.69 million +1.5%N/A6.3 $29.16 4/15/20222,590,000 shares $93.63 million +0.8%N/A6.3 $36.15 3/31/20222,570,000 shares $93.98 million -8.2%N/A5.9 $36.57 3/15/20222,800,000 shares $93.32 million -7.9%N/A6.2 $33.33 2/28/20223,040,000 shares $105.18 million -6.2%N/A6.3 $34.60 2/15/20223,240,000 shares $121.40 million +12.5%N/A6.7 $37.47 1/31/20222,880,000 shares $98.15 million +14.3%N/A6.5 $34.08 1/15/20222,520,000 shares $99.62 million +2.0%N/A6 $39.53 12/31/20212,470,000 shares $122.02 million +13.8%N/A6.7 $49.40 12/15/20212,170,000 shares $98.00 million +14.2%N/A6.1 $45.16 11/30/20211,900,000 shares $95.29 million +11.8%N/A5.7 $50.15 11/15/20211,700,000 shares $97.22 million -9.6%N/A5 $57.19 10/29/20211,880,000 shares $104.06 million +27.0%N/A5.5 $55.35 10/15/20211,480,000 shares $93.92 million -0.7%N/A4.3 $63.46 9/30/20211,490,000 shares $106.13 million +5.7%N/A4.1 $71.23 9/15/20211,410,000 shares $105.50 million +4.4%N/A3.3 $74.82 8/31/20211,350,000 shares $90.61 million -6.3%N/A2.8 $67.12 8/13/20211,440,000 shares $84.17 million -4.6%N/A3 $58.45 7/30/20211,510,000 shares $75.65 million +0.7%N/A3.1 $50.10 7/15/20211,500,000 shares $77.64 million -8.0%3.4%3.1 $51.76 6/30/20211,630,000 shares $83.80 million -23.8%3.7%3.5 $51.41 6/15/20212,140,000 shares $111.22 million +24.4%4.9%4.8 $51.97 5/28/20211,720,000 shares $50.17 million -3.9%3.9%4.3 $29.17 PRTA Short Interest - Frequently Asked Questions What is Prothena's current short interest? Short interest is the volume of Prothena shares that have been sold short but have not yet been covered or closed out. As of April 30th, traders have sold 6,871,465 shares of PRTA short. 14.65% of Prothena's shares are currently sold short. Learn More on Prothena's current short interest. What is a good short interest ratio for Prothena? The short interest ratio, also known as the "days to cover ratio", is calculated by dividing the number of shares of a stock sold short divided by its average trading volume. A short interest ratio ranging between 1 and 4 generally indicates strong positive sentiment about a stock and a lack of short sellers. A short interest ratio of 10 or greater indicates strong pessimism about a stock. PRTA shares currently have a short interest ratio of 18.3. Learn More on Prothena's short interest ratio. Which institutional investors are shorting Prothena? As of the most recent reporting period, the following institutional investors, funds, and major shareholders have reported short positions of Prothena: Caption Management LLC. These positions are disclosed in Form 13F filings with the Securities and Exchange Commission. What is a good short interest percentage for Prothena? Companies that have a short interest as a percentage of float below 10% indicates positive investor sentiment and few short sellers. Stocks with a short interest percentage above 10% is considered high, suggesting some investors are pessimistic about the stock. Companies with a short interest percentage of 20% or more indicates widespread negative sentiment. 14.65% of Prothena's floating shares are currently sold short. Is Prothena's short interest increasing or decreasing? Prothena saw a decrease in short interest in the month of April. As of April 30th, there was short interest totaling 6,871,465 shares, a decrease of 2.9% from the previous total of 7,076,832 shares. Changes in short volume can be used to identify positive and negative investor sentiment. Investors that short sell a stock are betting that its price will decline in the future. An increase in short sale volume suggests bearish (negative) sentiment among investors. A decrease on short sale volume suggests bullish (positive) sentiment. How does Prothena's short interest compare to its competitors? 14.65% of Prothena's shares are currently sold short. Here is how the short interest of companies in the industry of "pharmaceutical products" compare to Prothena: Sarepta Therapeutics, Inc. (25.35%), Phibro Animal Health Corporation (6.01%), Ascentage Pharma Group International - Unsponsored ADR (0.00%), Stoke Therapeutics, Inc. (23.12%), Bausch Health Cos Inc. (2.15%), Ocular Therapeutix, Inc. (11.59%), Mesoblast Limited (2.76%), Tyra Biosciences, Inc. (14.81%), Aurinia Pharmaceuticals Inc (7.87%), Zymeworks Inc. (9.57%), Which stocks are the most shorted right now? As of the most recent reporting period, the following stocks had the largest short interest positions: SPDR S&P 500 ETF Trust ($86.09 billion), Invesco QQQ ($39.89 billion), iShares Russell 2000 ETF ($26.13 billion), Western Digital Corporation ($12.66 billion), Salesforce Inc. ($12.29 billion), Sandisk Corporation ($11.87 billion), SPDR S&P Biotech ETF ($9.82 billion), Lumentum Holdings Inc. ($8.51 billion), iShares 20+ Year Treasury Bond ETF ($7.76 billion), and Bloom Energy Corporation ($7.40 billion). View all of the most shorted stocks. What does it mean to sell short Prothena stock? Short selling PRTA is an investing strategy that aims to generate trading profit from Prothena as its price is falling. PRTA shares are trading down $0.17 today. To short a stock, an investor borrows shares, sells them and buys the shares back on the public market later to return it to the lender. Short sellers are betting that a stock will decline in price. If the stock does drop after selling, the short seller buys it back at a lower price and returns it to the lender. The difference between the sell price and the buy price is the trader's profit. How does a short squeeze work against Prothena? A short squeeze for Prothena occurs when it has a large amount of short interest and its stock appreciates in price. This forces short sellers to cover their short interest positions by buying actual shares of PRTA, which in turn drives the price of the stock up even further. How often is Prothena's short interest reported? Short interest is typically published by a stock exchange once per month. However, NASDAQ publishes a report for U.S. stocks, including PRTA, twice per month. The most recent reporting period available is April, 30 2026. What do PRTA's short interest metrics mean? Understanding short interest metrics can help you assess how traders are positioning around a stock like PRTA:Shares Sold Short: The total number of shares that have been sold by short sellers but have not yet been covered or closed out. A high number may indicate bearish sentiment.Short Float: The percentage of a company’s publicly available shares (or "float") that are sold short. A higher short float suggests a greater portion of the stock is being bet against.Days to Cover (Short Interest Ratio): This estimates how many days it would take short sellers to cover their positions, based on average daily trading volume. Higher values can signal potential for a short squeeze if buying pressure increases.These metrics are often used by traders to gauge sentiment, volatility risk, and the potential for price movements based on short covering activity. More Short Interest Resources from MarketBeat Related Companies Sarepta Therapeutics Short Squeeze Phibro Animal Health Short Squeeze Ascentage Pharma Group International Short Squeeze Stoke Therapeutics Short Squeeze Bausch Health Cos Short Squeeze Ocular Therapeutix Short Squeeze Mesoblast Short Squeeze Tyra Biosciences Short Squeeze Aurinia Pharmaceuticals Short Squeeze Zymeworks Short Squeeze Short Interest Tools Stocks to Short Largest Short Interest Positions Short Interest Increases Short Interest Decreases Short Interest Reporting Dates This page (NASDAQ:PRTA) was last updated on 5/19/2026 by MarketBeat.com Staff. 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