You probably think you own the "whole" stock market. Most people do. They buy an S&P 500 fund, see names like Apple and Nvidia, and feel like they’ve covered all their bases.
But you haven't. Honestly, you're missing thousands of companies.
That's where the Dow Jones US Completion Total Stock Index comes in. It is, quite literally, the "everything else" of the American equity market. If the S&P 500 is the varsity team, this index is the rest of the school—the scrappy mid-caps, the volatile small-caps, and the micro-cap companies that most investors don't even know exist until they've already tripled in price.
It's a massive, sprawling list of stocks. It represents the total U.S. market minus the stocks in the S&P 500. Think of it as the ultimate completionist tool for a portfolio.
Why Does This Index Even Exist?
Wall Street loves to slice and dice things. The Dow Jones US Completion Total Stock Index was built to solve a very specific problem: overlap.
Imagine you have a big chunk of money in an S&P 500 fund. You decide you want more exposure to smaller companies, so you buy a "Total Stock Market" index fund. Suddenly, you've doubled down on Microsoft and Amazon because those total market funds are market-cap weighted. The big guys crush the small guys. You aren't actually diversifying; you're just getting heavier at the top.
By using the completion index, you bypass the giants. It picks up exactly where the S&P 500 leaves off.
The Anatomy of the Completion Index
This isn't some niche, tiny list. We're talking about roughly 3,000 stocks.
While the S&P 500 focuses on large-cap stability, the Dow Jones US Completion Total Stock Index is a chaotic, beautiful mix of sectors. You’ll find mid-cap stalwarts that are just a few billion dollars shy of the "big leagues" alongside biotech startups that might not have a product yet.
It’s weighted by float-adjusted market capitalization. This means the bigger "small" companies have more influence than the truly tiny ones. It’s a dynamic list. When a company like Tesla or Uber finally gets "called up" to the S&P 500, this index spits them out. They’ve outgrown the completion phase.
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Conversely, when a former giant falls from grace and gets booted from the S&P 500, they often land right back here. It’s the safety net and the launching pad all at once.
The Mid-Cap Sweet Spot
A huge portion of this index is comprised of mid-cap stocks. These are often the "Goldilocks" of investing.
They are bigger and more stable than tiny startups, so they don't go bankrupt quite as easily. But they are small enough that they can still double or triple their revenue in a few years—something Apple simply cannot do at its current scale.
You'll see names in here that you recognize from your daily life, but aren't quite "Magnificent Seven" level yet. Think of companies in the industrial space, regional banks, or specialized tech firms.
Performance: Is it Actually Better?
Here is the thing about the Dow Jones US Completion Total Stock Index: it’s a roller coaster.
If you look at long-term charts, small and mid-caps have historically outperformed large-caps over very long horizons. But—and this is a big "but"—they come with gut-wrenching volatility. In a bull market where everyone is chasing "growth at any price," the completion index can fly. In a recession or a high-interest-rate environment, these companies often get hammered.
Why? Because smaller companies usually have harder times getting cheap loans compared to a cash-rich giant like Alphabet.
Kinda makes sense, right?
If you looked at 2023, the S&P 500 demolished almost everything else because of the AI craze focused on the biggest tech names. The completion index felt like a laggard. But go back to different eras, and the script flips entirely. Diversification isn't about winning every year; it’s about not losing everything when one specific sector or size-class fails.
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How Regular People Actually Trade This
You can't buy "The Index" directly. No one can. It’s just a math formula maintained by S&P Dow Jones Indices.
Instead, you look for the vehicles that track it. The most famous version of this isn't even labeled "Dow Jones" in your brokerage account. Most people encounter this through the Vanguard Extended Market Index Fund (VEXAX) or its ETF twin, VXF.
These funds aim to replicate the Dow Jones US Completion Total Stock Index as closely as possible.
- Expense Ratios: Because it’s an index fund, the costs are usually dirt cheap. You aren't paying a fund manager to "pick" winners; you're paying a computer to buy everything that isn't in the S&P 500.
- Tax Efficiency: These funds tend to be pretty efficient because they don't flip stocks constantly. They only sell when the index changes.
- The "Completion" Strategy: Many 401(k) plans offer an S&P 500 fund and an "Extended Market" fund. If you hold both in the right proportions—usually about 80% S&P and 20% Extended—you have effectively created a Total Stock Market fund.
The Risks Nobody Mentions
Investors love to talk about the "upside" of small caps. They dream of finding the next Amazon while it's still trading in the completion index.
But there’s a darker side.
The Dow Jones US Completion Total Stock Index contains a lot of "zombie" companies. These are businesses that barely earn enough to pay the interest on their debt. In the S&P 500, you have a committee that acts as a gatekeeper; they generally require companies to be profitable before they join.
The completion index has no such filter. If it’s public and it’s not in the S&P 500, it’s probably in here. You are buying the losers along with the future winners.
Also, liquidity can be an issue. If you’re a massive hedge fund trying to move billions, you can’t move in and out of some of these smaller names without moving the price. For you and me? Not a big deal. For the market at large? It adds to the "jerkiness" of the index’s movements.
Is It Right for You?
Honestly, it depends on your stomach.
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If you’re 25 and have forty years of work ahead of you, owning the Dow Jones US Completion Total Stock Index is almost a no-brainer. You want that exposure to the smaller, high-growth engines of the economy. You can afford to watch the index drop 30% in a bad year because you know the recovery potential is massive.
If you’re 64 and planning to retire next Tuesday? Maybe take it easy. The volatility might be more than your heart (or your bank account) can handle.
Actionable Steps for Your Portfolio
Don't just read about it. If you want to use this index to actually change your financial picture, here is how you do it.
Check your current holdings. Most people are "large-cap heavy." Look at your 401(k) or IRA. If you see that 100% of your US stocks are in an S&P 500 tracker, you are missing out on the "completion" effect.
Calculate your ratio. To mimic the entire U.S. economy, the magic number is usually around 82% Large Cap (S&P 500) and 18% Extended Market (the completion index). Some people round it to 80/20 for simplicity.
Look for the ticker VXF. This is the Vanguard Extended Market ETF. It’s one of the most liquid ways to get this exact exposure. BlackRock and State Street have their own versions, but Vanguard is the 800-pound gorilla here.
Ignore the daily noise. Small caps can go through "lost decades" where they underperform the big guys. If you decide to buy into the completion index, you have to commit to it for at least five to ten years. Otherwise, you’re just gambling on market sentiment.
The Dow Jones US Completion Total Stock Index isn't flashy. It doesn't get the headlines that the Dow 30 or the Nasdaq 100 get. But for the serious investor who wants to actually own the American dream—every car dealership, every biotech lab, and every software startup—it is the only way to truly finish the puzzle.