S&P MidCap 400 — Scored by 5 Investment Models

Think of the MidCap 400 as the proving ground. These ~400 companies, with market caps of $8.0–22.7 billion at addition, have already demonstrated they can build a real business. Many are category leaders in niche industries, regional banks expanding nationally, or specialty manufacturers that dominate markets too small for the mega-caps to bother with. The index forms the middle tier of the S&P Composite 1500.

Like the S&P 500, the MidCap 400 screens companies when they are added: positive earnings, adequate liquidity, and sufficient public float. The S&P Dow Jones Indices committee reconstitutes the index quarterly. Companies that grow large enough graduate to the S&P 500; those that shrink too far drop to the SmallCap 600. This natural turnover means the index constantly refreshes itself with companies in the most dynamic phase of their lifecycle.

What the return research shows is narrower than it is often made to sound. Banz (1981) first documented that smaller US stocks had earned higher average returns, and Fama and French (1992) confirmed the size effect. Whether it persists is disputed: it has been weak and uneven since, and long stretches favor large caps. Past returns do not predict future ones.

Growth runway.Mid-cap companies are still scaling — expanding into new markets, launching product lines, and gaining market share. They have the financial resources to invest aggressively without the constraints of saturated end-markets that slow many large-caps.

Less analyst coverage.Mid-caps are followed by fewer analysts than S&P 500 companies, so a systematic score covers ground fewer professional opinions do. That is coverage, not an edge: our backtest found no statistically significant excess return from the scores.

Graduation.When a MidCap 400 company is promoted to the S&P 500, index funds tracking the S&P 500 must buy the stock. Shleifer (1986) found that stocks added to the S&P 500 rose on the news; Greenwood and Sammon (2025) find that this index effect has shrunk from about 7% in the 1990s to under 1% in the last decade.

Sector diversification.The MidCap 400 is less tech-heavy than the S&P 500. Industrials and Financials carry more weight, providing broader exposure to the physical economy. This can serve as a natural hedge against tech-sector drawdowns.

AlphaStocks applies the same 5-model composite methodology to mid-cap stocks as to the S&P 500. Every stock receives a score from 0 to 10, blending Quality (40%), Value (10%), Momentum (35%), and Timing (15%).

The Quality axisis especially important for mid-caps. While the S&P 400's quality screen filters out unprofitable companies, not all profitable companies are high-quality businesses. The Piotroski and Buffett models show which mid-caps have consistent margins, strong returns on equity, and improving financial health on their filings.

The Timing axis — min(Value, Momentum)— is a critical safeguard in the mid-cap space. Mid-cap value traps matter here because, with fewer analysts watching, a deteriorating business can take longer to be re-priced. The Timing axis prevents the composite from rewarding a cheap stock that the market is actively selling.

Sector calibration ensures fair comparisons within the mid-cap universe. A mid-cap regional bank is evaluated with banking-specific metrics, not generic ratios designed for software companies.

The S&P MidCap 400 sits between the S&P 500 (large-caps, $22.7B+ at addition) and the S&P SmallCap 600 (small-caps, $1.2B–$8.0B at addition). Together, all three form the S&P Composite 1500, covering ~90% of US equity market capitalisation.

For a detailed comparison of size segments and their risk-return characteristics, see Large-Cap vs. Mid-Cap vs. Small-Cap: Which Is Right for You?