The 500 Total Market Split Just Got a Lot More Lopsided

I’ve watched this exact setup play out before.

You buy the S&P 500 total market split thinking you’re getting broad exposure. Then you check the holdings and realize seven companies are doing most of the heavy lifting. Nvidia is over 6% of the index. Microsoft, Apple, Amazon, Meta, Google, and Tesla fill out the rest of the top seven. Together they’re north of 30% of the entire S&P 500’s market cap.

That’s not diversification. That’s a leveraged bet on mega-cap tech with 493 other stocks as window dressing.

Meanwhile, total market ETFs — the ones that hold the S&P 500 plus mid-caps and small-caps — give you exposure to roughly 4,000 companies. Sounds better. Except those extra 3,500 names have been getting crushed while the big seven run. The performance gap over the past two years isn’t small. It’s double digits.

So which one do you pick? The answer depends on whether you think concentration keeps working, or whether you’re willing to own the boring stuff that lags until it doesn’t.

What the 500 Total Market Numbers Actually Show

Let’s strip this down to what you actually own.

The S&P 500 tracks the 500 largest U.S. companies by market cap — market cap just means share price times shares outstanding, the total value of the company. It’s weighted by size, so bigger companies move the index more. When Nvidia jumps 3%, your S&P 500 fund feels it. When a mid-cap utility drops 3%, you barely notice.

A total market ETF holds the S&P 500 and adds mid-cap and small-cap stocks. You’re getting around 4,000 total names. The extra exposure tilts you toward companies with market caps between $300 million and $10 billion — the ones building infrastructure, running regional banks, manufacturing components. Less headline juice, more economic breadth.

Here’s the kicker: Nvidia’s single 6%+ weighting is larger than the entire energy sector in the S&P 500. One chipmaker outweighs Exxon, Chevron, and every oil company in the index combined. If you think AI infrastructure keeps scaling, that concentration makes sense. If chip demand stalls or margins compress, you’re holding a very large bag.

Why Total Market Funds Lagged (and When They Don’t)

For the past two years, total market ETFs underperformed the S&P 500 by a wide margin. The reason is simple: small and mid-caps got hammered by rising rates and tighter credit conditions. These companies borrow more, have thinner margins, and can’t muscle through a downturn the way mega-caps can.

Meanwhile, the Magnificent Seven printed record earnings and poured capital into AI. Investors piled in. The S&P 500 rode that wave. Total market funds held the same seven stocks, but they were diluted by thousands of laggards.

Concentration works until everyone believes it always works. That’s when it stops working.

History shows the reversals are sharp. In the late 1990s, tech concentration peaked. The Nasdaq lost 78% over the next two years. In , financials dominated the S&P 500. Then they collapsed and didn’t recover for a decade. The setup is never identical, but the pattern repeats: concentration drives outperformance, then it unwinds fast.

Total market funds give you a cushion. When mega-caps stumble, smaller companies — especially those tied to domestic demand, infrastructure, or less-crowded sectors — can hold up or even rally. You won’t capture all the upside when tech rips, but you won’t eat all the downside when it reverses.

Does the AI Boom Change the Calculation?

Nvidia’s projected chip sales are doubling. Hyperscalers are spending tens of billions on data centers. AI infrastructure is real, and it’s accelerating. The question isn’t whether the spending is happening — it is. The question is whether that growth is already priced in at current valuations.

When a company’s weight in the index is above 6%, the market is pricing in years of flawless execution. A single margin miss, a delay in next-gen chips, or a shift in customer spending can trigger a sharp repricing. And because the S&P 500 is so concentrated, that repricing moves the entire index.

Total market funds won’t save you from a tech correction, but they dilute the damage. The extra 3,500 stocks include industrials, healthcare, consumer staples, and regional players that benefit from AI buildout indirectly — construction, power infrastructure, component suppliers. Those names won’t 10x, but they also won’t lose half their value if Nvidia’s guidance disappoints.

Which One Should You Actually Own?

For most people, the answer is both, but in different proportions depending on your tolerance for concentration risk.

If you believe mega-cap tech dominance continues for the next several years, the S&P 500 is cleaner. You get maximum exposure to the companies driving earnings growth and market returns. The expense ratios are nearly identical — around 0.03% for most broad index funds — so cost isn’t the differentiator.

If you think concentration is a risk, or you want exposure to economic growth beyond the top seven names, total market funds make more sense. You’ll lag during mega-cap rallies, but you’ll participate more evenly when leadership rotates. And rotation always happens — the only question is when.

Metric	S&P 500	Total Market
Number of holdings	~500	~4,000
Top 7 concentration	30%+	~24%
Small/mid-cap exposure	0%	~20%
2-year performance vs S&P	Baseline	-12% to -15%
Expense ratio (typical)	0.03%	0.03%

One approach: core position in total market, with a tilt toward the S&P 500 if you want to overweight large-caps. Or split 60/40 between the two and rebalance annually. The key is knowing what you own and why, not just buying “the index” because someone said it’s safe.

What Happens When the Concentration Trade Breaks?

No one rings a bell at the top. The reversal starts with a single earnings miss, a macro shock, or a rotation into cheaper sectors. Then momentum flips. The stocks that led for years suddenly lag, and the laggards catch a bid.

In , the Nasdaq peaked in March and lost 78% by October . In , high-growth tech peaked in November and many names dropped 60% to 80% within a year. The S&P 500 held up better both times because it had exposure beyond tech — but it still fell 49% in – and 25% in .

Total market funds won’t protect you from a broad selloff, but they smooth the extremes. When mega-caps correct hard, the damage is spread across thousands of names instead of concentrated in seven. That difference matters more in drawdowns than in rallies.

The math is boring but it’s real: lower concentration means lower volatility over full cycles. You give up some upside to avoid some downside. Whether that’s worth it depends on how you sleep when your portfolio drops 20% in a month.

Is the S&P 500 riskier now than it was five years ago?

Yes. Five years ago, the top 10 stocks were around 22% of the index. Today they’re over 33%. That’s a 50% increase in concentration. More weight in fewer names means bigger swings when those names move. If Nvidia and Microsoft both drop 10% in a week, the S&P 500 can fall 2% just from those two stocks.

Do total market ETFs cost more to own?

No. Expense ratios for both are nearly identical, typically 0.03% to 0.04% annually. That’s $3 to $4 per year for every $10,000 invested. Cost isn’t the reason to choose one over the other — concentration and exposure are.

Can you just buy both and call it diversified?

You can, but it’s redundant. The S&P 500 is about 82% of the total market by weight, so buying both just overweights large-caps. If you want true diversification, pick the total market fund and add a small-cap or international tilt separately. Doubling up on the 500 doesn’t add much.