Fund overlap: why an S&P 500 fund, a Nasdaq fund and a tech fund are mostly one bet
Three tickers, three names, three line items. The look-through often shows one bet wearing three labels.
Holding several funds feels like diversification. Three tickers, three names, three line items in the brokerage app. The look-through often shows one bet wearing three labels.
The mechanism is simple. If two funds hold the same companies at similar weights, owning both does not spread your money; it concentrates it on the shared names and adds a fee for the privilege. We measured this on the combinations retail investors build most.
Pair Vanguard's S&P 500 fund (VOO) with the Invesco Nasdaq-100 fund (QQQ), a common core-plus-growth setup. Run the two at 50/50 and the funds overlap by 51%, measured as the shared weight where both funds hold the same stock. Just over half of what you own through one fund, you already own through the other.
The effect on concentration is direct. The combined portfolio is 41.4% in its top 10 and 36.4% in the seven megacaps. Nvidia reaches 8.1% of the whole portfolio and Apple 7.2%, both held through both funds. You did not buy a second fund; you bought more of the first one's largest positions.
Now build the portfolio many people actually hold: 40% VOO, 30% QQQ, 30% a technology sector fund such as Vanguard's VGT. Three funds, three names, the sense of a spread bet.
The look-through:
A 32-stock effective count from three "diversified" funds is not a spread bet. It is a concentrated position in megacap technology, assembled by accident and charged three management fees.
The contrast makes the point. Take the standard three-fund portfolio: 60% total US market (VTI), 30% total international (VXUS), 10% total bond market (BND).
The funds were chosen to cover different things, so they do. Overlap is not bad in itself; overlap you did not intend is, because it turns a fee you are paying for breadth into a fee you are paying for repetition.
The same trap exists outside the US tickers, with a twist. A European investor pairing the iShares Core MSCI World UCITS ETF (IWDA) with QQQ at 70/30 ends up with the two funds overlapping by 37%, because MSCI World is already about 62% US and led by the same megacaps QQQ holds. The combined book runs Nvidia at 6.4% and a 32% top-10. "Global plus a bit of US tech" turns out to be "US tech, twice."
That feeds a second, quieter form of doubling: home and country bias. MSCI put the US at 63% of the global equity universe in April 2025 and noted US-listed stock ETFs run about 80% domestic. A "world" fund that is 62% US, paired with anything US-tilted, leaves a portfolio far more concentrated in one country and one sector than its fund names suggest.
Two checks catch most of it:
ETF Trace computes both: paste your funds and weights, and it returns the pairwise overlap between every pair and each company's true weight across the lot, with the holdings date on each fund. Try it at etftrace.com.
About the data: portfolio figures are computed by ETF Trace's look-through engine from each fund's most recent holdings on file (VOO, VTI, QQQ dated 2026-03-31; IWDA dated 2026-06-15; VXUS and BND as filed). Overlap is the sum of the smaller of the two funds' weights on each shared security. US funds come from SEC Form N-PORT, European UCITS funds from the issuer's published holdings. The MSCI figure is linked to its source.