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ProthenaPRTA +6.66%74 5-Year Share Buyback Ratio is -5.70 as of Jun. 2026. GuruFocus rates PRTA with a GF Score™ of 74/100 and a GF Value™ of $12.96 (Modestly Undervalued). The stock has 2 warning signs investors should review. Among 1,131 Biotechnology companies, Prothena ranks better than 64.19% on this metric.
Shares Outstanding (EOP) are shares that have been authorized, issued, and purchased by investors and are held by them.
5-Year Share Buyback Ratio measures the average annual proportion of a company's outstanding shares repurchased over the past five years. It is calculated as the annualized percentage change in shares outstanding from five years ago to the current year. A positive ratio may indicate share buybacks over the period, while a zero or negative ratio may reflect no repurchases or potential share issuance. Prothena's current 5-Year Share Buyback Ratio was -5.70%.
PRTA's 5-Year Share Buyback Ratio is ranked better than 64.19% of 1131
companies
in the Biotechnology industry
Industry Median: -10.3
vs PRTA: -5.70
Prothena (NAS:PRTA) 5-Year Share Buyback Ratio Explanation
A negative number means the company might be issuing new shares. A positive number indicates that the company is buying back shares.
Be Aware
Investors usually like share buybacks. But as pointed by Warren Buffett, only if a company buys back shares at the prices below the stock's intrinsic value, it rewards remaining shareholders. If a company buys its overvalued stocks back, it destroys shareholder value.
Prothena 5-Year Share Buyback Ratio Related Terms
PRTA vs KYTX, QTTB, RZLT: 5-Year Share Buyback Ratio Comparison
For the Biotechnology subindustry, Prothena's 5-Year Share Buyback Ratio, along with its competitors' market caps and 5-Year Share Buyback Ratio data, can be viewed below:
* Competitive companies are chosen from companies within the same industry, with headquarter located in same country, with closest market capitalization; x-axis shows the market cap, and y-axis shows the term value; the bigger the dot, the larger the market cap. Note that "N/A" values will not show up in the chart.
Prothena 5-Year Share Buyback Ratio vs Biotechnology Industry
For the Biotechnology industry and Healthcare sector, Prothena's 5-Year Share Buyback Ratio distribution charts can be found below:
* The bar in red indicates where Prothena's 5-Year Share Buyback Ratio falls into.
This is the annualized percentage change in shares outstanding from five years ago to the current year. The annualized percentage change is calculated with least-square regression based on the latest six years of annual data on Shares Outstanding (EOP).
Please click Growth Rate Calculation Example (GuruFocus) to see how GuruFocus calculates Wal-Mart Stores Inc (WMT)'s revenue growth rate. You can apply the same method to get the average dividends per share growth rate.
What does a 5-Year Share Buyback Ratio of -5.70 mean?
Prothena (PRTA) has a 5-Year Share Buyback Ratio of -5.70 as of Jun. 2026. The 5-Year Share Buyback Ratio measures the average annual proportion of a company's outstanding shares repurchased over the past five years. It is calculated as the annualized percentage change in shares outstanding from five years ago to the current year. View historical data for Prothena and its competitors. According to the industry distribution chart, Prothena ranks #405 out of 1131 companies in the Biotechnology industry, placing it in the top 35.8%.
Is Prothena's 5-Year Share Buyback Ratio too high?
Prothena's current 5-Year Share Buyback Ratio is -5.70. Based on the distribution chart, Prothena ranks #405 out of 1131 companies in the Biotechnology industry, which is above the industry midpoint. Overall, Prothena has a GF Score™ of 74/100 and is considered Modestly Undervalued, reflecting its overall financial health beyond just this single metric.
How does Prothena's 5-Year Share Buyback Ratio compare to KYTX and QTTB?
According to the Biotechnology industry distribution chart, Prothena ranks #405 out of 1131 companies for 5-Year Share Buyback Ratio. This puts Prothena in the upper half of its industry. See the competitive comparison table and distribution chart on this page for a detailed peer-by-peer breakdown.
What is a good 5-Year Share Buyback Ratio for a Biotechnology company?
A good 5-Year Share Buyback Ratio depends on the Biotechnology industry context. However, 5-Year Share Buyback Ratio should not be evaluated in isolation — investors should consider it alongside profitability, growth, and financial strength metrics. Use the industry distribution chart on this page to see where any company falls relative to its peers.
What does a high 5-Year Share Buyback Ratio mean?
A high 5-Year Share Buyback Ratio can signal that a stock is expensive relative to its fundamentals. The 5-Year Share Buyback Ratio measures the average annual proportion of a company's outstanding shares repurchased over the past five years. It is calculated as the annualized percentage change in shares outstanding from five years ago to the current year. View historical data for Prothena and its competitors. Prothena's current 5-Year Share Buyback Ratio is -5.70. However, context matters — high-growth companies often justify higher valuations. Always evaluate alongside other metrics like GF Score™ and GF Value™.
Is Prothena stock overvalued right now?
Based on GuruFocus' analysis, Prothena (PRTA) is currently considered Modestly Undervalued. The stock's GF Value™ is $12.96, compared to a current price of $9.29 — trading 28.3% below its estimated fair value. The current 5-Year Share Buyback Ratio is -5.70. Prothena's overall GF Score™ is 74/100 with 2 warning signs to review. Investors should evaluate multiple metrics — including profitability, growth, and financial strength — before making a decision.
How is 5-Year Share Buyback Ratio calculated?
5-Year Share Buyback Ratio is calculated from a company's financial statements. For Prothena (PRTA), the current 5-Year Share Buyback Ratio is -5.70 as of Jun. 2026. GuruFocus calculates this using data sourced from SEC filings and annual reports. See the calculation section and 30-year financial data on this page for the full breakdown.
Is Prothena (PRTA) Overvalued in 2026?
Based on GuruFocus' analysis, Prothena stock appears to be undervalued.
The current stock price of $9.29 is trading 28.3% below its estimated GF Value™ of $12.96.
GuruFocus considers Prothena to be Modestly Undervalued.
Key valuation signals for PRTA:
5-Year Share Buyback Ratio: -5.70
GF Value™: $12.96 vs. price of $9.29 (28.3% below fair value)
No single metric tells the full story. See the PRTA stock analysis page for a complete view including 30-year financials, guru trades, and insider activity.
Prothena Corp PLC is a late-stage clinical biotechnology company that focuses on protein dysregulation and a pipeline of investigational therapeutics with the potential to change the course of devastating neurodegenerative and rare and peripheral amyloid diseases. Prothena is developing and applying its proprietary CYTOPE technology to target a broad spectrum of intracellular disease pathways in the brain and periphery. The company's pipeline includes both wholly-owned and partnered programs like Prasinezumab, Coramitug (PRX004), BMS-986446 (PRX005), PRX019, TDP-43 CYTOPE, and PRX012-TfR, being developed for the potential treatment of Parkinson's disease, ATTR amyloidosis with cardiomyopathy, Alzheimer's disease, Amyotrophic lateral sclerosis (ALS), and other neurodegenerative diseases.
74GF Score
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