The S&P 400 Index

The S&P MidCap 400 Index, often referred to as the S&P 400, is a stock market index that tracks the performance of 400 mid-sized publicly traded companies in the United States. It is maintained by S&P Dow Jones Indices and was introduced in 1991.

S&P MidCap 400 component stocks

Here are some key aspects of the S&P 400:

• Focus on Mid-Cap Companies: Unlike the S&P 500 which focuses on large-cap companies, the S&P 400 specifically targets companies with medium market capitalization. This segment of the market is often seen as representing a balance between the growth potential of smaller companies and the stability of larger ones.
• Market Capitalization Weighting: Similar to the S&P 500, the S&P 400 is weighted by free-float market capitalization. This means that companies with larger market values have a proportionally greater influence on the index’s performance.
• Representation of the Mid-Cap Segment: The index aims to reflect the distinctive risk and return characteristics of the U.S. mid-cap market. It is considered a benchmark for this segment of the equity market.
• Component of the S&P Composite 1500: The S&P MidCap 400 is one of three indices (along with the S&P 500 and the S&P SmallCap 600) that together form the S&P Composite 1500. These three indices provide non-overlapping coverage of different size segments of the U.S. equity market.
• Selection Criteria: Companies are selected for inclusion based on criteria such as market capitalization, liquidity, sector representation, and financial viability (e.g., positive earnings). The market cap range for eligibility evolves over time.
• Rebalancing: The index is typically rebalanced quarterly.

Performance:

As of September 12, 2025, the S&P 400 Index closed at 3,282.09.

The S&P 400 provides investors with exposure to a crucial part of the market that sits between large-cap and small-cap stocks, offering a different investment profile than the broader S&P 500.