This page tracks how heavily Prothena Corporation (LSE:0Y3M) is being shorted: ORTEX's daily short interest estimate, the cost to borrow the shares, utilization of the lendable supply and days to cover, next to the official exchange-reported figure.

Short interest

The number of shares that have been sold short and not yet bought back, usually shown as a percentage of free float (the shares available to trade). ORTEX estimates it every day from securities-lending data, instead of waiting for exchange reports that are published only twice a month and about two weeks late.

Cost to borrow

The annualised fee a short seller pays to borrow the shares, as a percentage of the position's value. A rising cost to borrow means lendable shares are getting scarce and holding the short is getting more expensive.

Utilization

The share of the lendable supply of a stock that is currently on loan. Close to 100% means almost no shares are left to borrow.

Days to cover

Short interest divided by average daily trading volume: roughly how many days of normal trading it would take for every short seller to buy back their shares.

Exchange-reported short interest

The official figure published by the exchange or regulator (in the US, FINRA twice a month). It is accurate but delayed, which is the gap the ORTEX daily and intraday estimates fill.

Source: ORTEX. Some figures are limited on the free view; live data and full history are part of ORTEX Advanced.

0Y3M key data

Prothena Corporation (LSE: 0Y3M) has a market capitalization of $448.28M. Last close $8.57 (as of 2026-11-12); 52-week range $7.82 to $11.66. ORTEX data as of 2026-10-27: short interest was 3.32% of free float, 638.2 days to cover and the average cost to borrow was 0.27%. Sign up for live short interest data.

About this data: 0Y3M short interest, cost to borrow and days to cover