Your Index Fund Is Hiding a 41% Tech Bet — How to See and Tame Concentration in One Sheet
The top 10 names in the S&P 500 now account for more than 40 percent of the index, and every one of them is a tech or AI company. The "diversified" label on your 401(k) and your brokerage has stopped matching the math. Here is how to see the real concentration and what to do about it in a single Google Sheet.
The News at a Glance
| S&P 500 Top 10 Weight | ~37% of the index (41% at end of 2025) |
| A Decade Ago | Top 10 was 19% of the S&P 500 |
| Top 10 P/E | 37x — roughly 40% above the rest of the index |
| AI Stock Share | ~53% of S&P 500 by weight (Bloomberg) |
| VOO Tech Weight | 39% of the Vanguard S&P 500 ETF |
| VTI Tech Weight | 42% of the Vanguard Total Stock Market ETF |
| NVDA in SPY | ~8% of fund assets (Nvidia alone) |
| 2027 Catalysts | SpaceX, Anthropic, OpenAI likely index additions |
The S&P 500 is no longer a proxy for the U.S. economy. It is a proxy for the AI trade. That is not a critique of the index — it is what happens when the largest companies dominate and they all happen to be in the same sector. The problem is not the exposure itself. The problem is that most investors do not know how much of it they actually own, because the same handful of stocks shows up in three different "diversified" funds they bought in three different years.
The Math Behind the Hidden Bet
When a handful of stocks make up more than a third of an index, the index stops behaving like a broad market. A 35 percent drawdown in the top seven — a routine bear-market move for high-beta tech — is roughly a 12 percent hit to the entire S&P 500, before any knock-on selling in the rest of the market. A 50 percent drawdown in those names, the kind several of them actually did in 2022, is closer to a 17 or 18 percent index decline. That is the math the "diversified" label is not telling you.
The next leg is already in motion. The S&P 500 committee kept the 12-month waiting period for index inclusion, which means SpaceX, Anthropic, and OpenAI are likely to join the index in 2027. SpaceX alone is expected to take 3 to 4 percent of the index on day one. The others will follow. Every passive dollar that tracks the S&P 500 will be forced to buy them, and the concentration in AI names will deepen rather than dilute. Most household 401(k) and IRA money is implicitly long all of it.
That is not a prediction. It is a description of how a market-cap-weighted index works. The S&P 500 buys more of whatever has grown the most, and the AI complex has grown the most. The label on the wrapper — "diversified," "broad market," "core" — does not change the math. It just hides it from anyone who is not actually looking.
Why the Overlap Stays Hidden
Most retail investors with a multi-brokerage setup hold something like an S&P 500 fund in their 401(k), a total market fund in their Roth, and a tech ETF in their taxable brokerage. On paper those look like three different positions. In practice, the same five to ten tickers drive more than half of the return in all three, and the concentration compounds across accounts. None of the brokerage apps show that. Each one shows you the holdings inside its own account, in isolation, with no concept of "you already own this in your other account."
That is the gap. A position that shows up in VOO, VTI, and a sector ETF is not three positions. It is one position, repeated. If Nvidia is 8 percent of SPY and you also hold 3 percent of your net worth in QQQM, your real Nvidia exposure is well over 10 percent of your portfolio, and a 50 percent drawdown in NVDA hits you for five points across three different "diversified" wrappers. You only see that when every account is in one place.
How to Track Concentration in One Sheet
The fix is not to dump your index funds. The fix is to know what you actually own. Pull every fund across every brokerage into a single Google Sheet, list the top 10 holdings of each, and count how many times each underlying ticker appears. Sum the percentage of your net worth allocated to each underlying name across all accounts. Then flag any single ticker that crosses 5 percent of your total portfolio, and any single sector (typically technology and AI today) that crosses 30 percent. The numbers will surprise you, and they will not match what any single brokerage app is showing.
From there, the options are straightforward and well-documented. Add an equal-weight S&P 500 ETF (RSP) to reduce mega-cap tech weight by roughly 11 percentage points without leaving the index. Add an international fund (VXUS) to bring in non-U.S. exposure, where technology is a much smaller share of the market. Add a dividend or small-cap value fund (SCHD, VIG, or a small-value ETF) to balance the growth tilt. The goal is not to avoid the AI trade. The goal is to make sure one trade is not the only thing driving the outcome.
None of this requires predicting the next 12 months. It requires making sure the next 12 months do not have to go one specific way for you to be okay. That is the entire point of diversification, and it is the thing a sheet that holds every account at once finally lets you check.
Frequently Asked Questions
How much of the S&P 500 is in the top 10 stocks?
As of mid-2026, the top 10 holdings of the S&P 500 sit at roughly 37 percent of the index by weight, and the top 10 ended 2025 at 41 percent — up from 19 percent a decade earlier. Every one of the top 10 is a technology or AI-focused company, and Bloomberg estimates that AI-related names now make up about 53 percent of the index by weight. A "broad market" fund is no longer a balanced bet; it is a leveraged position on a small group of AI names.
Why is my "diversified" index fund so tech-heavy?
Market-cap weighting means the S&P 500 buys more of whichever companies have grown the most. The largest technology and AI companies have grown the most, so the index automatically leans further into tech every quarter. The Vanguard S&P 500 ETF (VOO) holds 39 percent in technology, the Vanguard Total Stock Market ETF (VTI) holds 42 percent, and Nvidia alone represents about 8 percent of the SPDR S&P 500 ETF (SPY). When the same handful of names dominates every broad-market fund, holding three of them is not three separate bets. It is one bet, repeated.
How can I check index fund overlap and concentration in Google Sheets?
List every fund you own across every brokerage in one sheet, then pull the top holdings of each and count how many times each ticker appears. A position that shows up in VOO, VTI, and an S&P 500 fund is not three positions. It is one. From there, sum the percentage of your net worth that ends up allocated to each underlying ticker across all accounts, and flag any single name that exceeds 5 percent of the portfolio. InvestSheet automates this with built-in IVS_BROKERAGE formulas that return allocation, sector weight, and concentration from synced Fidelity, Schwab, Robinhood, and other accounts at once.
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