Prothena Corporation plc (PRTA) P/E Ratio History
Historical price-to-earnings valuation from 2021 to 2022
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PRTA Valuation Context
How does the current P/E compare to historical and market benchmarks?
P/E Ratio Analysis
As of May 8, 2026, Prothena Corporation plc (PRTA) trades at a price-to-earnings ratio of -2.3x, with a stock price of $10.53 and trailing twelve-month earnings per share of $-2.79.
The current P/E is 105% 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 22.3x, PRTA trades at a 110% discount to its sector peers. The sector includes 241 companies with P/E ratios ranging from 0.0x to 177.5x.
Relative to the broader market, PRTA trades at a notable discount to the S&P 500 median P/E of 25.1x. 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 P/E vs Peers
P/E ratio compared to closely matched public peers
| Company | Market Cap | P/E Ratio | PEG Ratio | EPS Growth (1Y) |
|---|---|---|---|---|
| $39B | 127.0 | - | +207%Best | |
| $28B | 21.7 | - | -21% | |
| $74B | 17.1Lowest | 2.70Best | +8% |
Peers sorted by market capitalization. P/E below peers may indicate undervaluation or lower growth expectations. Consider PEG ratio for growth-adjusted comparison.
PRTA Historical P/E Data (2021–2022)
Quarterly P/E ratios calculated from closing price and TTM EPS
| Quarter | Date | Price | TTM EPS | P/E Ratio | vs Avg |
|---|---|---|---|---|---|
| FY2022 Q1 | $36.57 | $1.22 | 30.0x | -38% | |
| FY2021 Q4 | Fri Dec 31 2021 00:00:00 GM | $49.40 | $1.09 | 45.3x | -6% |
| FY2021 Q3 | $71.23 | $1.03 | 69.2x | +44% |
Average P/E for displayed period: 48.2x
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Start ComparisonPRTA — Frequently Asked Questions
Quick answers to the most common questions about buying PRTA stock.
Is PRTA stock overvalued or undervalued?
PRTA trades at -2.3x P/E, below its 5-year average of 48.2x. At the N/A percentile of historical range, the stock is priced at a discount to its own history.
How does PRTA's valuation compare to peers?
Prothena Corporation plc P/E of -2.3x compares to sector median of 22.3x. The discount suggests lower growth expectations or higher risk.
What is PRTA's PEG ratio?
PRTA PEG ratio is N/A. Above 2.0 indicates premium valuation relative to growth rate. Historical P/E data spans 2021-2022.