When you’re exploring the U.S. stock market, you’ll quickly find that different indices measure different slices of the market. The Dow Jones U.S. Completion Total Stock Market Index — often shortened to the Completion Index — is one of those important yet under-appreciated slices. Simply put, it captures all U.S. stocks outside the S&P 500.
Think of the U.S. market like a giant puzzle. The S&P 500 index, with its 500 large companies you’ve probably heard of, forms a big piece of that puzzle. The Completion Index fills in almost all the rest — mid-cap, small-cap, and even micro-cap companies — giving you a far broader view of the U.S. equity universe.
In more technical terms, it’s a sub-index within the Dow Jones U.S. Total Stock Market family, and it includes all eligible stocks in that total market index that are not part of the S&P 500.
Why “Completion”? Because It Completes a Total Market View
Here’s an easy way to picture it:
- S&P 500 = the 500 largest, most established U.S. companies (large-cap).
- Dow Jones U.S. Completion Total Stock Market Index = all other publicly traded U.S. companies not in the S&P 500 — roughly 4,000 stocks spanning mid, small, and micro caps.
- Together, they form the entire U.S. stock market. If you combine both, you’re looking at virtually everything that’s investable in U.S. equities.
That’s why many serious investors see the Completion Index as a building block for total market exposure — which simply means owning a piece of almost every publicly listed U.S. company.
How It Works: Simple But Comprehensive
The Completion Index doesn’t use fancy filters like profitability or liquidity tests. Instead it uses a straightforward rule:
➡️ It includes all U.S. stocks in the Total Stock Market Index.
➡️ It excludes anything already in the S&P 500.
This means:
- It captures companies at all stages of growth — from established mid-caps to fast-growing small-caps.
- It naturally includes new IPOs and companies that haven’t yet met big-cap criteria but still play a role in the economy.
The weight of each stock in the index is based on market capitalization — bigger companies have more influence on the index’s performance, but because this index has such a large number of components, no single company dominates like Apple or Microsoft might in other benchmarks.
Putting It Into Context — A Real Example
Let’s consider a simple scenario:
Imagine two tech companies:
- Company A is a household name with a huge market cap — it’s in the S&P 500.
- Company B is an emerging tech firm with innovative products but a smaller market cap — not yet big enough for the S&P 500.
Company A helps define the performance of big-cap benchmarks. Company B, along with thousands like it, influences the Completion Index — together reflecting the broader growth trends of less-magnified parts of the market. (EBC Financial Group)
This matters because smaller companies often grow faster than big ones (albeit with more volatility). Including them gives you a more complete picture of how the economy and corporate America are evolving.
Performance and What It Means for Investors
While headline figures vary year to year, the Completion Index tends to show a different risk-return profile compared to large-cap indices:
- It may outperform during strong economic expansions, especially when smaller companies thrive on innovation and consumer demand. nversely, it can lag during downturns, when investors flee to large, stable companies.
Recent market data illustrates its real-world performance: as of late 2025, the index has shown steady movement with typical volatility you’d expect given its size and diversity.
How Investors Actually Use the Completion Index
Most investors don’t buy the index itself — they invest through funds or ETFs designed to track its performance. These investment vehicles make putting its diversification to work much easier.
Common strategies include:
1. Total Market Investing
Investors combine a large-cap fund (like one tracking the S&P 500) with a Completion Index fund to replicate the entire U.S. stock market.
2. Small & Mid-Cap Exposure
Because of the smaller companies it captures, the Completion Index can serve as a proxy for more growth-oriented stocks, balancing large-cap holdings.
3. Core-Satellite Strategies
Some investors use a broad index (core) and add targeted positions (satellites) in emerging sectors or themes — with the Completion Index often serving as part of the core.
For example, an investor might hold:
- 60% S&P 500 index fund
- 40% Completion Index fund
Together, this mix mirrors the total U.S. stock market.
Beyond the Numbers: What You Should Know
A key reason the Completion Index doesn’t make front-page headlines like the S&P 500 is simply visibility — most financial media focuses on big names. But for anyone serious about understanding the full U.S. market, the Completion Index offers valuable clarity.
It’s analogous to understanding both the blockbuster films and the independent movies in a film industry — together they show the full creative and economic picture, not just the blockbusters.
Conclusion — Why It Matters
The Dow Jones U.S. Completion Total Stock Market Index isn’t just another financial statistic. It’s a cornerstone of total market investing, capturing the vast universe of U.S. equities that lie beyond the familiar face of the S&P 500.
By filling in the gaps — from mid-sized companies to the nimble, up-and-coming small caps — it reveals trends and opportunities that large-cap indexes alone can miss. Whether you’re building a diversified portfolio or simply trying to understand how the U.S. stock market behaves as a whole, this index deserves a spot in your financial vocabulary.