What Is the Wilshire Mid-Cap Index?

The Dow Jones Wilshire Mid-Cap Index is a mid-cap benchmark index maintained by Wilshire Indexes, launched in 1996. The Wilshire US Mid-Cap Index is a float-adjusted, market capitalization-weighted index of the issues ranked between 500 and 1,000 by market capitalization of the Wilshire 5000 Total Market Index (Wilshire 5000).

Mid-cap (or mid-capitalization) is a term used to designate companies with a market cap between $2 and $10 billion. As the name implies, a mid-cap company falls in the middle between large-cap (or big-cap) and small-cap companies. 

Key Takeaways

  • The Wilshire Mid-Cap Index contains those Wilshire 5000 companies ranked between 500 and 1,000 by market value (with buffers).
  • The index is float-adjusted and capitalization-weighted, rebalanced semi-annually.
  • The components of the Wilshire US Mid-Cap are the bottom 250 Wilshire US Large-Cap securities and the top 250 Wilshire US Small-Cap securities by capitalization. 

Understanding the Wilshire Mid-Cap Index

The Wilshire (formerly Dow-Jones/Wilshire) Mid-Cap Index is a market-capitalization-weighted index that contains the companies ranked between 500 and 1,000 as measured by market capitalization.

The Wilshire Mid-Cap Index is the mid-cap subset of the Wilshire 5000 Composite Index. The Wilshire 5000 Composite Index, also known as the Wilshire 5000 Total Market Index, is the most broadly based U.S. stock index. Buffers are used to reduce index turnover.

Wilshire Midcap Sector Weights
Wilshire Midcap Sector Weights.

Other Wilshire Indices

Along with the Mid-Cap Index, there are three other segments of market capitalization, each with a different index association. The three other segments are the Wilshire U.S. Large-Cap Index, which includes stocks ranked 1 through 750, the Wilshire U.S. Small-Cap Index, with stocks ranked 751-2,500, and the Wilshire U.S. Micro-Cap Index, with the stocks that are ranked 2,501+.

The mid-cap index contains stocks from both the small- and large-cap indexes. It contains approximately 250 of the smallest large-cap stocks and 250 of the largest small-cap stocks.

The four indices together are known as the Total Market Index, a popular benchmark for investors as it proves a comprehensive broad-based coverage of the US market and includes the majority of stocks except those of the smallest value. The index represents the top 95% of the U.S. stock market based on market capitalization and includes around 3,600 stocks traded on U.S. stock exchanges.

Other Mid-Cap Indices

The Wilshire Mid-Cap Index is one of several indices that track mid-cap stocks. In addition to its core mid-cap index, Wilshire also offers mid-cap value and growth style indexes.

The Russell Midcap Index, for instance, is a market capitalization-weighted index comprised of 800 publicly traded U.S. companies with market caps of between $2 and $10 billion. The 800 companies in the Russell Midcap Index are the 800 smallest of the 1,000 companies that comprise the Russell 1000 Index.

The S&P MidCap 400 is an index published by Standard & Poor's. The index comprises 400 companies selected as broadly representative of companies with midrange market valuations of between $200 million and $5 billion.