The SPI comprises all securities traded on the SIX Swiss Exchange, at least 20% of which are freely traded; 215 securities are included (as of 2023). The weighting is based on the market capitalisation of the securities. The SPI is available both as a price index and as a total return index (calculation with gross dividends), whereby the abbreviation SPI usually denotes the total return index. The most important sub-indices are the SPI Large, SPI Middle and SPI Small as well as the SPI Extra.