The S&P BSE MidCap, often referred to as the BSE MidCap, is a benchmark index comprising mid-cap companies listed on the Bombay Stock Exchange. According to SEBI, companies that rank between 101 and 250 in terms of market capitalisation are categorised as mid-cap companies.

The S&P BSE MidCap index makes up about 15% of the total market capitalisation of the S&P BSE AllCap index. The top five sectors include consumer discretionary, financial services, healthcare, Industrials and Information Technology.

The index committee ensures that only stocks that feature in the S&P BSE AllCap index are considered. The constituents of the BSE AllCap index are ranked in descending order of their cumulative average daily total market capitalisation.

The top 70% of stocks are assigned to the BSE LargeCap index. The next 15% of stocks are included in the S&P BSE MidCap index. The index is subject to quarterly reviews in June, September, December and March and is rebalanced once every year in September.

The market capitalization of each stock is calculated as: Market Capitalisation = Current Market Price * Number of Outstanding Shares.

Once the market capitalisation is calculated, each stock is adjusted for free float by multiplying with a free-float factor: Free-Float Market Capitalisation = Market Capitalisation * Free-Float Factor. This ensures only publicly tradeable shares are considered.

Since the S&P BSE MidCap is an index, you cannot directly invest in it. However, there may be certain mutual funds that invest in the same constituents as the index in a bid to track and replicate its performance.

It is essential to note that the performance of the S&P BSE MidCap index is heavily dependent on market conditions, and investing in mid-sized companies comes with inherent risks. Thorough research and risk tolerance assessment is required before investing.