Prothena Corporation plc (PRTA): Short Interest History
The most recent FINRA short interest report for PRTA (settlement date August 14, 2026) shows 8,545,127 shares sold short , a change of 4.56% from the prior report .
Days to cover: 19.56.
FINRA settlement history
| Settlement date | Short interest | Change | Avg daily volume | Days to cover |
|---|---|---|---|---|
| Aug 14, 2026 | 8,545,127 | 4.56% | 436,939 | 19.56 |
| Jul 31, 2026 | 8,172,438 | -0.30% | 585,253 | 13.96 |
| Jul 15, 2026 | 8,196,964 | -2.06% | 499,741 | 16.40 |
| Jun 30, 2026 | 8,369,568 | 6.39% | 759,430 | 11.02 |
| Jun 15, 2026 | 7,866,857 | 1.67% | 492,334 | 15.98 |
| May 29, 2026 | 7,737,902 | 9.02% | 558,736 | 13.85 |
| May 15, 2026 | 7,097,854 | 3.29% | 547,700 | 12.96 |
| Apr 30, 2026 | 6,871,465 | -2.90% | 374,817 | 18.33 |
| Apr 15, 2026 | 7,076,832 | 0.87% | 461,513 | 15.33 |
| Mar 31, 2026 | 7,016,080 | -0.41% | 569,553 | 12.32 |
| Mar 13, 2026 | 7,044,790 | 2.77% | 628,888 | 11.20 |
| Feb 27, 2026 | 6,854,767 | -3.22% | 398,107 | 17.22 |
| Feb 13, 2026 | 7,083,043 | 0.27% | 390,797 | 18.12 |
| Jan 30, 2026 | 7,063,694 | -0.08% | 508,225 | 13.90 |
| Jan 15, 2026 | 7,069,471 | 7.36% | 490,187 | 14.42 |
| Dec 31, 2025 | 6,584,532 | 40.12% | 827,377 | 7.96 |
| Dec 15, 2025 | 4,699,126 | 1.29% | 692,839 | 6.78 |
| Nov 28, 2025 | 4,639,338 | -0.39% | 514,550 | 9.02 |
| Nov 14, 2025 | 4,657,490 | 12.39% | 631,094 | 7.38 |
| Oct 31, 2025 | 4,144,115 | 7.44% | 513,944 | 8.06 |
| Oct 15, 2025 | 3,857,015 | 0.29% | 718,695 | 5.37 |
| Sep 30, 2025 | 3,845,694 | 2.17% | 764,721 | 5.03 |
| Sep 15, 2025 | 3,763,878 | -7.19% | 830,200 | 4.53 |
| Aug 29, 2025 | 4,055,435 | -3.09% | 1,041,258 | 3.89 |
Frequently asked questions
What is short interest in PRTA?
Short interest is the total number of PRTA shares currently sold short but not yet covered or closed out. FINRA publishes this data twice monthly.
How is PRTA short interest calculated?
Short interest is aggregated from member firm reports to FINRA. Every U.S. broker-dealer must report aggregate short positions in each security as of the 15th and last trading day of each month.
What does a high short interest mean?
Higher short interest can indicate bearish sentiment, but it also raises the potential for a short squeeze if positive news forces short sellers to cover their positions simultaneously. Compare short interest to float (short percent of float) for context.