The MDAX is a stock index which lists German companies trading on the Frankfurt Stock Exchange. The index is calculated by Deutsche Börse. Until 2021 included the 60 Prime Standard shares from sectors that rank immediately below (in value of market capitalization) the originally 30 companies included in the DAX index; in 2021, the number of constituents in the MDAX shrank to 50 from 60. The company size is based on terms of order book volume and market capitalization. The index is based on prices generated in the electronic trading system Xetra.