The S&P BSE 100 stock index tracks the performance of the top 100 most liquid organisations listed on the Bombay Stock Exchange (BSE). These companies, classified as mid- or large-cap, contribute to the BSE 100 index. Changes in the BSE 100 share price have a direct impact on the index's value.

The list of BSE 100 companies is reviewed and revised twice a year, in June and December. The BSE also generates a dollar-based counterpart of the BSE SENSEX 100 called Dollex-100, which reflects the index's value in USD.

Companies eligible for the BSE 100 index must have been listed for at least three months, have large-cap or mid-cap classification, and stocks must be traded on at least 95% of the days in the previous three months.

Companies' revenue should be derived primarily from their main line of business, and a company's annualised traded value should exceed 10 million.

First, determine a company's market capitalisation by multiplying total shares by current market price. Then determine the percentage of shares available for free trade — the free-float factor — excluding closely held stocks.

Multiply the free-float factor by the market capitalisation to get the float-adjusted market capitalisation. For example, for Company XYZ with 2 lakh shares at Rs. 300 and 70% free float: Market cap = Rs. 6 crores; Float-adjusted market cap = Rs. 4.2 crore.

The same approach is used for all 100 businesses in the BSE 100 index. The float-adjusted market capitalisation of all 100 companies is taken together and compared to the base year market capitalisation (1983-1984) and multiplied by the base value of 100.

You can invest in individual stocks by researching companies listed in the BSE 100 index, or invest in mutual funds or ETFs that track the performance of the BSE 100 index.

Open a Demat account at a brokerage firm, execute your trades, monitor your investments regularly, and periodically assess and rebalance your portfolio to stay within your intended asset allocation.