Ever feel like you’re missing out on the "real" stock market? You probably track the S&P 500 or the Dow Jones Industrial Average. Most people do. But those big names only tell part of the story—the story of the giants. If you want to see what’s actually happening with the thousands of companies that aren't household names, you need to look at the Dow Jones Total Completion Stock Market Index.
Honestly, it’s a mouthful. Let’s just call it the "Completion Index" or the DWCPF.
Basically, this index is the ultimate "leftovers" club, but in the best way possible. It takes the entire U.S. stock market and rips out the S&P 500. What’s left? Everything else. We’re talking about the mid-caps that are actually growing, the small-caps that might be the next big thing, and the micro-caps that most Wall Street analysts can’t even find on a map.
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What is the Dow Jones Total Completion Stock Market Index anyway?
The concept is simple. If you take the Dow Jones U.S. Total Stock Market Index—which is supposed to represent basically every liquid stock in the country—and subtract the 500 companies sitting in the S&P 500, you get the Completion Index.
It’s designed to "complete" a portfolio.
Imagine you already own an S&P 500 index fund. You’ve got Apple, Microsoft, and Amazon. You’re heavy on tech giants. But you have zero exposure to the scrappy companies in the Russell 2000 or the mid-sized firms that have outgrown their "startup" boots but aren't quite "blue chip" yet. The Dow Jones Total Completion Stock Market Index fills that exact gap.
The Math Under the Hood
This isn't some equal-weighted gimmick. It’s a float-adjusted market-capitalization-weighted index.
That means the bigger companies within this "small" universe still carry more weight. If a company like Snowflake or Marvell Technology grows, it moves the needle more than a tiny micro-cap in Nebraska. The index rebalances quarterly. It’s a living, breathing list that currently holds over 3,000 constituents.
Think about that. 3,000+ companies.
While the S&P 500 covers about 80% of the U.S. market value, this index covers the "missing" 20%. It might sound like a small slice of the pie, but that 20% is where the most aggressive growth usually hides.
Why Investors Actually Care About DWCPF
You’ve probably heard of the "S Fund" if you work for the government or are in the military. The Thrift Savings Plan (TSP) uses the Dow Jones Total Completion Stock Market Index as the benchmark for its S Fund.
Millions of people are invested in this index without even realizing it.
Small-Cap Premium: Real or Myth?
There’s this long-standing theory in finance called the "small-cap premium." The idea is that because small companies are riskier and less researched, they should provide higher returns over long periods to compensate investors for the headache.
Does it work? Sometimes.
In 2024 and 2025, we saw periods where mid and small-caps went on absolute tears as interest rate expectations shifted. When the Fed hints at cuts, these smaller companies—who often carry more debt than Cash-Rich Apple—tend to celebrate. Their borrowing costs go down, and their stock prices go up.
But it’s a double-edged sword.
When the economy looks shaky, the Dow Jones Total Completion Stock Market Index usually gets hit harder than the S&P 500. It’s more volatile. It’s "bumpier." You need a stronger stomach to hold this than you do for a boring dividend fund.
The "Hidden" Giants in the Index
You might think an index of "everything else" is just full of companies you’ve never heard of. You’d be wrong.
While it excludes the S&P 500, it includes some very familiar names that, for one reason or another (usually S&P committee rules or recent IPO status), aren't in the big 500 yet.
- Technology: Think of companies like Workday or Cloudflare before they hit the big leagues.
- Industrials: Rapidly growing firms like Vertiv Holdings.
- Consumer Trends: Roblox or DraftKings have often spent time in this "completion" space.
If you only track the Dow 30 or the S&P 500, you’re essentially waiting for a company to "arrive" before you buy it. By the time a company is added to the S&P 500, a huge chunk of its legendary growth has already happened. The Completion Index lets you capture the "teenage years" of a corporate giant.
Performance: S&P 500 vs. Completion Index
It’s not a competition, but everyone treats it like one.
Over the last decade, the S&P 500 has actually outperformed the completion index. Why? Because the "Magnificent Seven" (Nvidia, Microsoft, etc.) became so massive that they distorted everything.
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But history is cyclical.
There have been huge stretches—like the early 2000s—where the S&P 500 was flat as a pancake while the small and mid-caps in the completion index were doubling.
- Average Market Cap: In the S&P 500, it's massive (hundreds of billions).
- Completion Index Average: It’s much lower, often around $2 billion to $15 billion.
- Sector Diversification: You’ll find way more Real Estate (REITs) and smaller Financials here than you will in the tech-heavy S&P.
[Image comparing the sector weightings of the S&P 500 versus the Dow Jones US Completion Index]
How to Actually Invest in It
You can't "buy" an index. You have to buy a fund that tracks it.
If you're a DIY investor, you’re looking for "Extended Market" funds.
- Vanguard Extended Market ETF (VXF): This is one of the most popular ways to get exposure. It tracks the S&P Completion Index, which is almost identical to the Dow Jones version.
- Fidelity Extended Market Index Fund (FSMAX): A staple for 401(k) plans.
- TSP S Fund: If you have a TSP account, this is your vehicle.
Most of these have incredibly low expense ratios. We’re talking 0.05% or less. It’s a cheap way to own 3,000 companies.
What Most People Get Wrong
The biggest misconception is that the Dow Jones Total Completion Stock Market Index is a "small-cap index."
It’s not.
It’s an Extended Market index. There is a huge difference. A small-cap index (like the Russell 2000) only looks at the bottom. The Completion Index includes Mid-Caps. These are companies worth $10 billion or $20 billion. They aren't small. They are just... not in the S&P 500.
Because it includes mid-caps, it’s actually less volatile than a pure small-cap fund, but more exciting than a large-cap fund. It’s the "Goldilocks" of market exposure for many.
Actionable Insights for Your Portfolio
If you’re looking at your brokerage account right now and wondering if you should add this, here’s how to think about it:
- Check your overlap. If you own a "Total Stock Market" fund (like VTSAX or VTI), you already own this. Do NOT buy a completion fund on top of a total market fund unless you want to intentionally overweight small companies.
- The 80/20 Rule. A classic "complete" portfolio is 80% S&P 500 and 20% Dow Jones Total Completion Stock Market Index. This gives you a market-weight exposure to the entire U.S. economy.
- Rebalance when things get crazy. If the S&P 500 has a huge year and the Completion Index lags, your 80/20 split might look like 85/15. That’s usually the signal to sell some of the winners and buy more of the completion index.
- Tax-Loss Harvesting. Because this index is volatile, it’s a great candidate for tax-loss harvesting in taxable accounts during market dips.
Stop thinking of the stock market as just 500 companies. There is a whole world of "completion" out there that drives the innovation and employment of the country. Whether you use the S Fund or a Vanguard ETF, getting a piece of the Dow Jones Total Completion Stock Market Index is basically betting on the "rest of America"—and historically, that's been a pretty smart bet.
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To get started, look at your current holdings and calculate your "large-cap drift." If more than 90% of your money is in the top 500 companies, you're not as diversified as you think. Consider a 10% to 15% allocation to an extended market fund to capture the growth of the next generation of market leaders.