Prothena Corporation plc (PRTA) P/E Ratio History
Deep ValueTrading at -1.7x · 0th percentile of 5-year range · Significant discount to historical valuation · Data 2021–2022
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P/E Ratio Analysis
As of November 6, 2026, Prothena Corporation plc (PRTA) trades at a price-to-earnings ratio of -1.7x, with a stock price of $7.89 and trailing twelve-month earnings per share of $-0.84.
The current P/E is 104% below its 5-year average of 48.2x. Over the past five years, PRTA's P/E has ranged from a low of 30.0x to a high of 69.2x, placing the current valuation at the 0th percentile of its historical range.
Compared to the Healthcare sector median P/E of 25.5x, PRTA trades at a 107% discount to its sector peers. The sector includes 231 companies with P/E ratios ranging from 0.0x to 195.9x.
Relative to the broader market, PRTA trades at a notable discount to the S&P 500 median P/E of 26.4x. Investors should consider the company's growth prospects, competitive position, and earnings quality when evaluating whether the current valuation is justified.
For a comprehensive intrinsic value estimate using discounted cash flow analysis, see our PRTA DCF Valuation Calculator →
Note: P/E ratio is just one valuation metric. It does not account for balance sheet strength, cash flow quality, or growth sustainability. Always conduct comprehensive due diligence before making investment decisions.
PRTA Cross-Benchmark Valuation
How does the current P/E compare to sector peers and the broader market?
PRTA P/E vs Peers
Neurodegeneration Drug Developers peers sorted by market cap
| Company | Market Cap | P/E Ratio | PEG Ratio | EPS Growth (1Y) |
|---|---|---|---|---|
| $21B | 67.2 | - | +207%Best | |
| $36B | 27.6 | - | -21% | |
| $93B | 21.8Lowest | 3.44Best | +8% |
Lower P/E can signal a discount or weaker growth expectations; PEG adds growth context.
PRTA Historical P/E Data (2021–2022)
Quarterly P/E ratios calculated from closing price and TTM EPS
| Quarter | Period End | Price | TTM EPS | P/E Ratio | vs Avg |
|---|---|---|---|---|---|
| FY2022 Q1 | - | $36.57 | $1.22 | 30.0x | -38% |
| FY2021 Q4 | Dec 31 2021 | $49.40 | $1.09 | 45.3x | -6% |
| FY2021 Q3 | - | $71.23 | $1.03 | 69.2x | +44% |
Average P/E for displayed period: 48.2x
PRTA Chart Terminal
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Intrinsic Valuation
DCF models, multiple analysis, and analyst estimates.
Historical Returns
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Peer Comparison
Compare growth, multiples, and margins vs sector.
PRTA — Frequently Asked Questions
Quick answers to the most common questions about buying PRTA stock.
What is PRTA's P/E ratio?
Prothena Corporation plc (PRTA) trailing twelve-month P/E ratio is -1.7x, based on TTM diluted EPS of $-0.84. The 5-year average P/E is 48.2x and the historical range spans 30.0x to 69.2x.
Is PRTA stock overvalued or undervalued?
PRTA trades at -1.7x P/E, below its 5-year average of 48.2x. At the 0th percentile of its historical range (30.0x–69.2x), the stock is priced at a discount to its own history.
Is PRTA stock expensive?
No, PRTA is not expensive on a historical basis. The current P/E of -1.7x is below the 5-year average of 48.2x and sits at the 0th percentile of its valuation range.
What is PRTA's historical P/E range?
Over the past 5 years, PRTA's P/E ratio has ranged from 30.0x to 69.2x, with a median of 45.3x and an average of 48.2x. The current P/E of -1.7x places the stock at the 0th percentile of this range. Full historical data spans 2021–2022.
How does PRTA's P/E compare to the S&P 500?
PRTA trades at -1.7x P/E versus the S&P 500 median of 26.4x. The 106% discount to the market suggests lower growth expectations or perceived higher risk.
How does PRTA's valuation compare to Healthcare peers?
Prothena Corporation plc P/E of -1.7x compares to the Healthcare sector median of 25.5x. The discount suggests lower growth expectations, weaker margins, or higher perceived risk relative to peers. See the peer comparison table on this page for ticker-by-ticker P/E and PEG.
What is PRTA's PEG ratio?
PRTA PEG ratio is N/A, based on a P/E of -1.7x and EPS growth of -99.6%. PEG normalises P/E by growth and helps compare stocks with different earnings trajectories.
What is PRTA's earnings yield?
PRTA earnings yield is N/A, the inverse of its -1.7x P/E ratio. Earnings yield represents the percentage of each dollar invested that the company earns. It can be compared directly to bond yields to assess relative attractiveness of stocks versus fixed income.