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HowShorted

PRTA short interest Nasdaq Global Market

Prothena Corporation plc Ordin. FINRA's reported shares short for this symbol, twice a month by settlement date, shown as the regulator publishes them. No percentage is shown: an SEC filer exists but no defensible share count is available yet.

Shares short
8,544,664
vs previous settlement
+48,868 (+0.6%)
days to cover
26.53
Settlement date
15 Sep 2026

Shares short over time

Aggregate net short position time series for PRTA shares short

Days to cover

FINRA's own figure: reported shares short divided by the security's average daily trading volume, published alongside each settlement.

Aggregate net short position time series for PRTA days to cover

Fails to deliver

The SEC's fails-to-deliver figure for PRTA: the aggregate net balance of shares that failed to be delivered at each settlement date, published by the SEC twice a month and shown here verbatim for the trailing window. A balance is not a daily flow, and a fail has many ordinary causes; the SEC says it cannot guarantee the accuracy of the data. See what fails to deliver are and the largest balances today.

Last balance on file
535
11 Sep 2026
Highest in window
25,569
24 Dec 2025
Days with a balance
66
Window
16 Sep 2025 to 14 Sep 2026
Aggregate net short position time series for Prothena Corporation plc Ordin fails to deliver

Source: U.S. Securities and Exchange Commission, fails-to-deliver data (public domain). Only settlement days with a positive balance appear; the largest balance in the window was 26K shares.

History

Every FINRA settlement we hold for PRTA, newest first. สณ marks a figure FINRA itself flagged as revised.

Full reported short interest history
Settlement dateShares shortChangeDays to cover
15 Sep 20268,544,664+48,86826.53
31 Aug 20268,495,796โˆ’49,33124.85
14 Aug 20268,545,127+372,68919.56
31 Jul 20268,172,438โˆ’24,52613.96
15 Jul 20268,196,964โˆ’172,60416.40
30 Jun 20268,369,568+502,71111.02
15 Jun 20267,866,857+128,95515.98
29 May 20267,737,902+640,04813.85
15 May 20267,097,854+226,38912.96
30 Apr 20266,871,465โˆ’205,36718.33
15 Apr 20267,076,832+60,75215.33
31 Mar 20267,016,080โˆ’28,71012.32
13 Mar 20267,044,790+190,02311.20
27 Feb 20266,854,767โˆ’228,27617.22
13 Feb 20267,083,043+19,34918.12
30 Jan 20267,063,694โˆ’5,77713.90
15 Jan 20267,069,471+484,93914.42
31 Dec 20256,584,532+1,885,4067.96
15 Dec 20254,699,126+59,7886.78
28 Nov 20254,639,338โˆ’18,1529.02
14 Nov 20254,657,490+513,3757.38
31 Oct 20254,144,115+287,1008.06
15 Oct 20253,857,015+11,3215.37
30 Sep 20253,845,694+81,8165.03
15 Sep 20253,763,878โˆ’291,5574.53
29 Aug 20254,055,435โˆ’129,4063.89
15 Aug 20254,184,841โˆ’189,7843.34
31 Jul 20254,374,625โˆ’382,8295.42
15 Jul 20254,757,454+426,9225.48
30 Jun 20254,330,532โˆ’325,2311.73
13 Jun 20254,655,763+241,0363.84
30 May 20254,414,727โˆ’4,538,0211.47
15 May 20258,952,748+1,498,7873.72
30 Apr 20257,453,961โˆ’468,75111.94
15 Apr 20257,922,712โˆ’461,85811.94
31 Mar 20258,384,570โˆ’394,51618.37
14 Mar 20258,779,086โˆ’350,17919.66
28 Feb 20259,129,265+94,42221.30
14 Feb 20259,034,843+134,76930.98
31 Jan 20258,900,074โˆ’449,62726.45
15 Jan 20259,349,701สณ+579,44920.20
31 Dec 20248,770,252โˆ’27,5919.06
13 Dec 20248,797,843+740,54118.14
29 Nov 20248,057,302+180,08917.82
15 Nov 20247,877,213+345,59317.87
31 Oct 20247,531,620+746,42915.95
15 Oct 20246,785,191+1,485,00410.31
30 Sep 20245,300,187โˆ’422,5077.74
13 Sep 20245,722,694+127,82424.90
30 Aug 20245,594,870+214,41020.71
15 Aug 20245,380,460+4,20614.16
31 Jul 20245,376,254+606,84613.61
15 Jul 20244,769,408โˆ’331,38510.56
28 Jun 20245,100,793โˆ’1,555,6545.89
14 Jun 20246,656,447โˆ’55,21116.64
31 May 20246,711,658+196,81415.03
15 May 20246,514,844โˆ’234,74811.31
30 Apr 20246,749,592+121,79414.45
15 Apr 20246,627,798+162,26011.92
28 Mar 20246,465,538+216,12310.99
15 Mar 20246,249,415+183,86011.08
29 Feb 20246,065,555+254,2648.63
15 Feb 20245,811,291+63,8276.61
31 Jan 20245,747,464โˆ’514,3788.12
12 Jan 20246,261,842+182,9524.15
29 Dec 20236,078,890+263,6108.42
15 Dec 20235,815,280โˆ’1,033,5906.48
30 Nov 20236,848,870+655,23813.24
15 Nov 20236,193,632สณโˆ’308,8708.99
31 Oct 20236,502,502+1,420,6895.20
13 Oct 20235,081,813+689,2489.41
29 Sep 20234,392,565+116,75910.75
15 Sep 20234,275,806+159,19111.05
31 Aug 20234,116,615+414,6019.68
15 Aug 20233,702,014+31,4059.24
31 Jul 20233,670,609+26,38810.29
14 Jul 20233,644,221+124,91513.60
30 Jun 20233,519,306โˆ’162,5117.47
15 Jun 20233,681,817+362,9399.09
31 May 20233,318,878+104,5067.11
15 May 20233,214,372โˆ’55,6894.65
28 Apr 20233,270,061โˆ’3,03310.54
14 Apr 20233,273,094โˆ’439,4818.53
31 Mar 20233,712,575+264,6377.62
15 Mar 20233,447,938+361,9057.43
28 Feb 20233,086,033สณ+122,9146.52
15 Feb 20232,963,119+182,2306.61
31 Jan 20232,780,889โˆ’94,6367.58
13 Jan 20232,875,525+234,5393.81
30 Dec 20222,640,986+231,0734.57
15 Dec 20222,409,913+152,4343.76
30 Nov 20222,257,479+29,3735.05
15 Nov 20222,228,106โˆ’197,4543.69
31 Oct 20222,425,560โˆ’290,4224.05
14 Oct 20222,715,982โˆ’542,7003.68
30 Sep 20223,258,682+794,5851.69
15 Sep 20222,464,097โˆ’220,1594.30
31 Aug 20222,684,256+66,7508.11
15 Aug 20222,617,506โˆ’15,1198.85
29 Jul 20222,632,625โˆ’384,8439.37
15 Jul 20223,017,468โˆ’8,53511.39
30 Jun 20223,026,003โˆ’293,5286.65
15 Jun 20223,319,531โˆ’281,8589.32
31 May 20223,601,389+151,9858.75
13 May 20223,449,404+823,3695.97
29 Apr 20222,626,035+33,8915.66
14 Apr 20222,592,144+23,1397.66
31 Mar 20222,569,005โˆ’231,5307.71
15 Mar 20222,800,535โˆ’242,1716.56
28 Feb 20223,042,706โˆ’193,3656.29
15 Feb 20223,236,071+360,8127.92
31 Jan 20222,875,259+357,9135.98
14 Jan 20222,517,346+48,2764.56
31 Dec 20212,469,070+297,1235.20
15 Dec 20212,171,947+272,7984.81
30 Nov 20211,899,149+194,5294.74
15 Nov 20211,704,620โˆ’174,4597.09
29 Oct 20211,879,079+401,0086.14
15 Oct 20211,478,071โˆ’15,2285.00
30 Sep 20211,493,299+81,5364.55
15 Sep 20211,411,763+63,8524.01
31 Aug 20211,347,911โˆ’94,2712.73
13 Aug 20211,442,182โˆ’69,0135.17
30 Jul 20211,511,195+6,4084.25
15 Jul 20211,504,787โˆ’124,9492.67
30 Jun 20211,629,736โˆ’510,3572.21
15 Jun 20212,140,093สณ+421,7843.35
28 May 20211,718,309โˆ’67,7036.04
14 May 20211,786,012โˆ’238,1085.12
30 Apr 20212,024,120โˆ’25,12510.66
15 Apr 20212,049,245+167,6799.11
31 Mar 20211,881,566+949,6613.36
15 Mar 2021931,905โˆ’47,7672.54
26 Feb 2021979,672+270,6381.86
12 Feb 2021709,034+34,6741.15
29 Jan 2021674,360+28,1454.53
15 Jan 2021646,215โˆ’84,8504.67
31 Dec 2020731,065โˆ’707,6292.40
15 Dec 20201,438,694+154,8415.04
30 Nov 20201,283,853โˆ’28,7489.01
13 Nov 20201,312,601โˆ’85,5414.65
30 Oct 20201,398,142+95,2885.73
15 Oct 20201,302,854โˆ’37,7687.68
30 Sep 20201,340,622โˆ’291,3933.24
15 Sep 20201,632,015+155,0547.25
31 Aug 20201,476,961โˆ’55,1018.74
14 Aug 20201,532,062+207,12111.27
31 Jul 20201,324,941โˆ’63,7035.75
15 Jul 20201,388,644+58,5844.68
30 Jun 20201,330,060+309,9773.07
15 Jun 20201,020,083โˆ’68,6424.39
29 May 20201,088,725โˆ’192,4425.24
15 May 20201,281,167สณโˆ’25,0945.73
30 Apr 20201,306,261โˆ’226,2194.25
15 Apr 20201,532,480โˆ’52,9727.36
31 Mar 20201,585,452โˆ’45,5075.54
13 Mar 20201,630,959+78,3888.46
28 Feb 20201,552,571+41,4858.44
14 Feb 20201,511,086โˆ’220,74013.25
31 Jan 20201,731,826โˆ’79,78612.49
15 Jan 20201,811,612+31,46411.33
31 Dec 20191,780,148โˆ’169,8924.62
13 Dec 20191,950,040+3,55410.51
29 Nov 20191,946,486+189,8546.59
15 Nov 20191,756,632โˆ’45,6699.87
31 Oct 20191,802,301+60,01813.31
15 Oct 20191,742,283โˆ’91,32712.91
30 Sep 20191,833,610โˆ’141,4346.91
13 Sep 20191,975,044โˆ’100,30611.83
30 Aug 20192,075,350โˆ’83,8268.18
15 Aug 20192,159,176โˆ’100,94712.90
31 Jul 20192,260,123โˆ’93,45614.87
15 Jul 20192,353,579โˆ’54,28015.62
28 Jun 20192,407,859โˆ’268,7707.81
14 Jun 20192,676,629สณโˆ’140,3947.69
31 May 20192,817,023โˆ’52,3698.92
15 May 20192,869,392โˆ’167,5988.57
30 Apr 20193,036,990โˆ’287,51314.21
15 Apr 20193,324,503โˆ’178,17112.53
29 Mar 20193,502,674โˆ’308,21114.05
15 Mar 20193,810,885โˆ’90,60210.20
28 Feb 20193,901,487+59,5558.91
15 Feb 20193,841,932โˆ’74,9639.05
31 Jan 20193,916,895โˆ’146,25813.92
15 Jan 20194,063,153โˆ’373,8167.27
31 Dec 20184,436,969โˆ’554,5769.11
14 Dec 20184,991,545โˆ’217,42212.54
30 Nov 20185,208,967โˆ’45,28112.11
15 Nov 20185,254,248+84411.78
31 Oct 20185,253,404+49,6919.94
15 Oct 20185,203,713โˆ’164,99812.74
28 Sep 20185,368,711โˆ’719,4106.68
14 Sep 20186,088,121+17,09122.03
31 Aug 20186,071,030โˆ’194,50422.12
15 Aug 20186,265,534+208,88115.83
31 Jul 20186,056,653โˆ’100,22616.01
13 Jul 20186,156,879โˆ’94,04415.48
29 Jun 20186,250,923+1,415,3189.11
15 Jun 20184,835,605+688,3305.32
31 May 20184,147,275โˆ’322,1656.03
15 May 20184,469,440+138,5964.31
30 Apr 20184,330,844โˆ’784,5931.61
13 Apr 20185,115,437+787,7598.92
29 Mar 20184,327,678+732,8925.05
15 Mar 20183,594,786+295,38012.27
28 Feb 20183,299,406โˆ’54,10511.49
15 Feb 20183,353,511โˆ’1,394,7623.16
31 Jan 20184,748,273โˆ’706,67212.94
12 Jan 20185,454,945+215,11216.45
29 Dec 20175,239,833โ€“15.85

Scroll inside the table for earlier settlements, back to 29 Dec 2017.

Questions

Frequently asked questions

What is PRTA's short interest?
8,544,664 shares short for settlement date 15 Sep 2026, per FINRA's consolidated short interest report, up 48,868 from the previous settlement.
Why is there no percentage for PRTA?
Because no defensible share count exists to divide by: an SEC filer exists but no defensible share count is available yet. The symbol maps to an SEC filer, but its share count cannot be used yet. A newly listed company needs two cover-page counts on file before the first is trusted; a split or an unexplained jump pauses publication until a fresh SEC count corroborates it; a secondary share class publishes under the company's primary line; and a foreign filer's short count is in depositary-share units. This page upgrades to a percentage automatically once a defensible count exists.
What is PRTA's days to cover?
26.53 days for settlement date 15 Sep 2026: FINRA's own short interest ratio, the reported shares short divided by average daily trading volume, published in the same file and shown verbatim. We hold no volume data ourselves.
Is this the short float?
No. This page shows FINRA's share count only. Short float divides that count by the public float, and short interest as we publish it elsewhere divides it by shares outstanding from SEC filings. Neither denominator is available for this line, so neither ratio is shown.
How often does this update?
FINRA member firms report short positions as of the 15th and the last business day of each month, and FINRA publishes the consolidated figures about nine business days later. We ingest each file the day it appears and re-read recent settlements for revisions.

Ranked companies with a percentage: most shorted US stocks. Other symbols with counts only: shares short without a percentage. Browse by name: US companies A to Z.