The Barron’s 400 Index (Equal Weight): Hitting the Market’s Sweet Spot

Over the past three decades, mid-cap stocks have quietly outperformed their large- and small-cap counterparts. From 1995 to 2025, the Russell Midcap Index delivered an annualized return of 10.6%, exceeding the 10.4% gain for the Russell 1000 (large caps) and the 8.5% return for the Russell 2000 (small caps).

The story is similar across S&P’s size-based benchmarks. The S&P MidCap 400 Index returned 11.1% annually over the same 30-year period, compared to 10.4% for the S&P 500 and 9.9% for the S&P SmallCap 600.

In dollar terms, that difference compounds meaningfully over time: A $100 investment in the S&P MidCap 400 Index 30 years ago would be worth $2,387 today, compared to $2,014 in the S&P 500 and $1,757 in the S&P 600. (Figure 1)

Figure 1. 30-Year Cumulative Growth in S&P’s US Equity Size Indexes

Figure 1. Illustration of a $100 investment in each index on September 1, 1995. All figures are based on the indexes’ monthly total returns, through August 29, 2025. One cannot invest in an index. Source: FactSet

What Constitutes a Mid Cap?

While “mid cap” is a familiar term to most investors, there’s no universally accepted definition of what qualifies as a mid-sized company. Each index provider has its own approach to size classifications, which can shift over time as markets evolve. Still, understanding how major index providers define mid caps helps clarify why the Barron’s 400 Index (EW)—and the Barron’s 400 ETF (BFOR) that tracks it—is widely considered a mid cap strategy.

Russell Indexes

The Russell Midcap Index, a popular benchmark for mid-sized companies, consists of the 800 smallest firms in the Russell 1000 Index—roughly the bottom 80% of the large-cap universe, representing about 27% of its total market capitalization. Its average market cap is $29.6 billion and its median market cap is $11.7 billion.

S&P Dow Jones Indices

The S&P MidCap 400 Index is another core mid-cap benchmark, but it takes a slightly different approach in determining its composition. It includes the next 400 companies by market cap after the S&P 500, with eligibility currently based on a range of approximately $8 billion to $22.7 billion. These thresholds are periodically updated, and actual constituent sizes may fall outside the strict bounds due to market movements. The index’s average and median market caps are $7.8 billion and $6.9 billion, respectively.

Morningstar

Morningstar’s size mapping methodology is relative, classifying stocks into size segments based on their percentage of total U.S. equity market capitalization. Mid caps fall in the 70th to 90th percentile, following large caps (top 70%) and preceding small caps (bottom 10%). This dynamic classification adjusts with market conditions and is widely used to categorize ETFs and mutual funds.

What unites these classifications is a shared purpose: to benchmark a segment of the market composed of companies that have moved beyond their early, more volatile growth stages, yet still retain meaningful upside potential. These are businesses that are generally stable and well-established, but still nimble enough to grow faster than their large-cap counterparts. This position—straddling the maturity of large caps and the dynamism of small caps—is what earns mid caps their reputation as the market’s “sweet spot.”

MarketGrader’s Overlapping Size Bands

MarketGrader follows a relative size mapping methodology similar to Morningstar’s, but introduces intentional overlaps between size groups to account for the fluid nature of market cap transitions and to enhance selection flexibility in our indexes. These bands are defined by the company’s position within the total U.S. market by capitalization, as shown below.

Figure 2. MarketGrader’s Size Mapping of the U.S. Equity Market

Source: MarketGrader

This overlapping structure provides a more granular view of the mid-cap segment, which—when including the shared zones with large and small caps—spans from 85% to 95% of the market.

Mapping the Barron’s 400 Index to MarketGrader’s Size Classification

Although the Barron’s 400 Index selects its constituents from the entire U.S. equity universe–except for very small companies with a market cap below $250 million–the difference in its two weighting schemes determines whether it behaves as a large cap index (MCW) or a mid cap index (EW). B400 EW, the subject of this article, assigns 0.25% weight to each constituent at each semi-annual rebalance, reducing the influence of mega cap stocks that dominate the benchmarks, and significantly increasing its exposure to mid and small cap names. A close look at how the current constituents of B400 (EW) map to the overall U.S. equity market makes this clear.

Figure 3 shows MarketGrader’s most recent size mapping from March 2025, our last semi-annual rebalance. It is based on market caps from the beginning of that month, and will be updated next week, when we complete our second rebalance of 2025.

Figure 3. MarketGrader SIze Mappings, U.S. Equity Market, March 2025

Source: MarketGrader

Figure 3 shows clearly how top heavy the U.S. Equity market has become, with only 507 companies, out of a total of 4,853, accounting for 85% of its aggregate market capitalization ($61.7 trillion out of $72.7 trillion). Incredibly, 3,061 companies, or 63% of the total, are classified as small caps, and have an aggregate market cap of a mere $1.5 trillion.

The mid cap segment of the market, according to MarketGrader’s mapping, including the overlapping areas with large and small caps, comprises 667 companies (14% of the total), with an aggregate market capitalization of $7.3 trillion, or 10% of the market’s total.

Figure 4 below illustrates how the current constituents of B400 map into our size classifications.

Figure 4. Barron’s 400 Index Mapping to MarketGrader’s U.S. Equity Market Size Categories

Source: MarketGrader

When market cap weighted, B400 leans even more towards large caps than does the overall U.S. market, with 94% of its weight in the Large Cap category, according to our mapping. This goes to show how much value MarketGrader’s rating system finds among the market’s largest companies, despite much richer valuations than their smaller counterparts. It also shows the value of having an equally weighted version of the index to give investors a more balanced access to the best companies in the U.S., based on our GARP + Quality analysis.

The mid cap segment of B400 comprises 119 companies, or 30% of the total. While this number might seem small relative to a total of 400 companies, consider that relative to the underlying universe, as shown in Figure 3, this is more than twice the weight of mid caps across all U.S. equities (30% to the universe’s 14%, based on company count).

Perhaps most useful to better understand the balance in B400 EW, is to look at the total weights per size category once the index’s equal weighting is taken into account. Figure 5 illustrates the impact on the makeup of the index when its constituents are equally weighted, compared to its market cap weighted sibling.

Figure 5. Differences in Size Mapping for B400 Based on Weighting Scheme

Sources: MarketGrader & FactSet

Conclusion

The equal-weighted version of the Barron’s 400 Index offers investors a differentiated and powerful way to access the market’s sweet spot. By selecting the 400 highest-rated U.S. companies based on MarketGrader’s GARP + Quality methodology—and then allocating equally to each—B400 EW avoids the concentration risk that plagues traditional benchmarks, while still maintaining exposure to the market’s most fundamentally sound large caps.

Its broad reach also ensures investors capture the potential of smaller companies on their way up the market cap spectrum—before they become household names. With more than twice the mid-cap representation of the overall U.S. equity universe, B400 EW delivers a balanced portfolio that reflects the dynamism of mid caps, the stability of high-quality large caps, and the long-term growth potential of emerging leaders.

For investors seeking a smarter core equity allocation, B400 EW offers a compelling, rules-based path to the middle ground that has historically outperformed both ends of the market cap spectrum.