S&P MidCap 400 Index

The S&P MidCap 400 is an index calculated by S&P Dow Jones Indices and made up of the shares of mid-sized US companies. Launched in 1991, it represents the segment that lies between the same provider's large-company and small-company indices. The index is designed to track the share performance of mid-sized companies as a separate segment.

Mid-sized companies are businesses that have moved past the early stages of growth but still have room to expand. The index weights these companies, which span sectors such as industrials, financials, consumer, real estate and technology, by their free-float shares. In selecting constituents, an index committee assesses criteria such as liquidity, public float and profitability.

Investors follow the MidCap 400 to see how the part of the US economy beyond the large companies is performing; this segment is often more sensitive to domestic demand and credit conditions. On Lzzo.com, the index is shown in points using Yahoo Finance data; prices of funds that track the index differ from this value.