The semi-annual review of Austrian indices by the Index Committee has resulted in a change of the composition of the ATX. STRABAG SE and PORR AG have been added to Austria's benchmark index, replacing Telekom Austria AG and Mayr-Melnhof Karton AG. The composition of the ATX is based on two key criteria: the average daily turnover on the stock exchange (liquidity) and free float capitalisation of the company.

PORR AG's inclusion in the ATX is accompanied by an increase in the free float factor from 0.5 to 0.6. Palfinger AG will also see an increase in its free float factor from 0.4 to 0.5. The free float factor indicates how many shares of a company are freely tradable – holdings of less than 4% are considered free float. The higher the factor, the greater the weight of the share in the index. All changes will take effect on 22 September. The next scheduled review of the composition of Austrian indices will take place in March 2026, the free float factors will be reviewed again in December 2025.

The ATX calculation is based on a purely quantitative methodology that is laid down in a set of rules. In accordance with the "The Rules for the Austrian Indices of the Vienna Stock Exchange", the Vienna Stock Exchange may add or remove companies after the semi-annual review (March and September). The calculation parameters (number of shares, free float factors and representation factors) are reviewed on a quarterly basis (March, June, September and December). Once a month, the Vienna Stock Exchange publishes the "ATX watchlist", which shows the ranking of stocks according to liquidity and capitalised free float. Institutional investors, trading members, issuers of financial products, academics and the Vienna Stock Exchange contribute their expertise to the Index Committee, which decides on the rules governing the indices.

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