Rather than a fixed number of "large cap" or "small cap" stocks, Morningstar uses a flexible system that isn't adversely affected by overall movements in the market. Large-cap stocks are defined as the group that accounts for the top 70% of the capitalization of the Morningstar domestic stock universe; mid-cap stocks represent the next 20%; and small-cap stocks represent the balance. The Morningstar stock universe represents approximately 99% of the U.S. market for actively traded stocks.
Historical Market Cap Breakpoints