Glossary
Mid-cap stock
A stock of a company with a medium market value, commonly between about $2 billion and $10 billion.
A mid-cap stock belongs to a company of medium size by market value, commonly placed between about $2 billion and $10 billion. Mid-caps sit between the established giants and the small, riskier firms: often past the start-up stage, with proven products, but still with room to grow, expand into new markets or become acquisition targets. They make up a distinct slice of the market that many diversified portfolios hold through dedicated funds.
Where the boundaries fall
The $2 billion to $10 billion range is a convention used by many brokers and fund companies, not a rule. Index providers set their own. Under S&P Dow Jones Indices guidelines effective July 1, 2025, companies eligible for the S&P MidCap 400 generally had market caps of about $8.0 billion to $22.7 billion, noticeably higher than the rule of thumb, because the index sits between the S&P 500 and the S&P SmallCap 600. FTSE Russell's Russell Midcap Index takes the smaller members of the Russell 1000.
How mid-caps behave
Mid-caps tend to be more volatile than large caps and less volatile than small caps, with growth rates and risks to match. They are generally liquid enough for most investors to trade easily. Like all size groups, they have had long stretches of beating and lagging the large-cap market, so past leadership by size says little about the next decade.