Prothena Corporation plc (PRTA) short interest & short volume · 21.6% of float short
Prothena Corporation plc official short interest (FINRA, twice monthly) and daily short volume (FINRA Reg SHO), with history, % of float and days to cover.
What changed
PRTA short interest was little changed at 7.9M shares in the Oct 15, 2026 report (21.6% of float, 13.3 days to cover). Daily short volume averaged 63.2% of volume over the last 20 sessions, down from 68.5% the 20 sessions before, the 67th percentile of its own 20-day averages since Sep 23, 2025.
Short interest
Official, twice monthly · settled Oct 15, 2026
- Shares short
- 7.9M
- prior 8.0M
- % of float
- 21.6%
- float 36.8M
- Days to cover
- 13.3
- avg vol 598K
- Change vs prior report
- -0.9%
Days to cover is short interest divided by FINRA's average daily volume for the period: how many average days of trading it would take shorts to buy back.
% of float uses the current float for every report (no float was stored with older reports).
Source: FINRA equity short interest (twice monthly) · Settlement Oct 15, 2026
Daily short volume
Share of each day's volume sold short · FINRA Reg SHO
- Latest (Nov 2)
- 69.5%
- 108K of 156K
- 20-day average
- 63.2%
- prior 68.5%
- Percentile vs own history
- 67th
- 233 periods since 2025
Loading prices…
Source: FINRA Reg SHO daily short sale volume · Latest Nov 2, 2026
Short squeeze score (model)
Price since settlement: -3.4%
Model, not a forecast: 40 pts short interest % of float (full at 30%), 25 pts days to cover (full at 10), 15 pts rise in short interest since the prior report (full at +50%), 20 pts price gain since the settlement date (full at +25%). Missing inputs score 0.
PRTA's squeeze score and its inputs with Lician Pro.Start 3-day trial — $149/yr
Market-wide: most shorted stocks, biggest changes and unusual short volume · PRTA overview
| Date | Short | Total | Short % of volume |
|---|---|---|---|
| 2026-11-02 | 108,288 | 155,696 | 69.5% |
| 2026-10-30 | 87,095 | 116,236 | 74.9% |
| 2026-10-29 | 54,465 | 82,852 | 65.7% |
| 2026-10-28 | 124,425 | 261,910 | 47.5% |
| 2026-10-27 | 90,408 | 176,599 | 51.2% |
| 2026-10-26 | 207,724 | 296,068 | 70.2% |
| 2026-10-23 | 119,450 | 170,876 | 69.9% |
| 2026-10-22 | 145,435 | 182,057 | 79.9% |
| 2026-10-21 | 116,503 | 171,265 | 68.0% |
| 2026-10-20 | 97,528 | 158,950 | 61.4% |
Healthcare peers with similar quant ratings
PRTA is rated 3.20 of 5 among 532 rated Healthcare stocks (Lician quant rating, Nov 4, 2026). How the rating works
- ALHC short interest3.23 · Hold · stock
- VRDN short interest3.22 · Hold · stock
- ALKS short interest3.21 · Hold · stock
- GILD short interest3.20 · Hold · stock
- NEOG short interest3.19 · Hold · stock
- BSX short interest3.18 · Hold · stock
- XNCR short interest3.18 · Hold · stock
- TNDM short interest3.17 · Hold · stock
PRTA short interest FAQ
What is PRTA's short interest?
Prothena Corporation plc (PRTA) had 7.9M shares sold short and not yet covered in FINRA's Oct 15, 2026 settlement report, 21.6% of its 36.8M-share float.
How many days to cover does PRTA have?
13.3 days: 7.9M shares short divided by an average daily volume of 598K for the Oct 15, 2026 period.
Is PRTA short interest rising or falling?
PRTA short interest was little changed (-0.9%) from 8.0M to 7.9M shares in the Oct 15, 2026 report.
Is PRTA a short squeeze candidate?
Lician's squeeze watch scores PRTA 54 out of 100 (elevated) from the Oct 15, 2026 report: short interest % of float 28.8/40, days to cover 25/25, change in short interest vs prior report 0/15, price change since settlement date 0/20. It is a transparent model of how crowded the short side is, not a forecast that a squeeze will happen.
What share of PRTA daily volume is sold short?
63.2% on average over the last 20 sessions to Nov 2, 2026 (FINRA Reg SHO daily short volume; the 67th percentile of its own 20-day averages). Short volume counts market makers' same-day short sales, so it is not short interest.
What was PRTA's latest FINRA short volume?
On Nov 2, 2026, cached FINRA short volume for Prothena Corporation plc (PRTA) was 108,288 shares, 69.5% of 155,696 total volume.
How many PRTA short-volume sessions are listed on this page?
This page lists 10 cached FINRA short-volume sessions for Prothena Corporation plc (PRTA), from Oct 20, 2026 through Nov 2, 2026.
How did PRTA short volume percent change from the prior cached session?
Cached FINRA short volume for Prothena Corporation plc (PRTA) moved from 74.9% on Oct 30, 2026 to 69.5% on Nov 2, 2026, down 5.4 percentage points.
Not investment advice. Figures as filed or reported, not a live feed.