ETF overlap — why owning multiple ETFs doesn’t always diversify

Buying VOO, VTI, QQQ, and SPY to “diversify” is a common retail pattern. It looks like spreading risk across four different products. In reality, more than 80% of the dollars point to the same dozen stocks. Here’s what overlap actually means.

What is ETF overlap?

Overlap is the fraction of one ETF’s holdings that also appear in another. If VOO holds 500 stocks and VTI holds 3,700, and they share 495 of those stocks, the overlap by count is high. But count overlap is the wrong metric.

Weight overlap is the sum of the minimum weight of each shared stock across both funds. If VOO holds AAPL at 7.1% and VTI holds AAPL at 6.4%, they overlap on AAPL by min(7.1, 6.4) = 6.4%. Sum that across every shared stock and you get the total weight overlap.

Because large-cap indexes are market-cap weighted, weight overlap is usually dramatically higher than count overlap. Two funds can share 95%+ of their dollars even when one has 6× more total holdings.

Common examples

• VOO + SPY: ~100% overlap — both track the S&P 500. The only difference is fee (0.03% vs 0.09%) and trading liquidity.
• VOO + VTI: ~80% overlap by dollars. VTI adds mid + small caps but still most of the dollars go to the same large-caps.
• VOO + QQQ: ~45% overlap. Both heavy in AAPL/MSFT/NVDA/ AMZN/META/GOOGL, which drives most returns.
• SCHD + VYM: ~35% overlap. Both dividend-focused but use different selection methodologies (Dow Jones 100 Dividend Achievers vs. FTSE High Dividend Yield).
• XLK + QQQ: ~55% overlap on top-10 holdings despite being different strategies (pure-tech sector vs. Nasdaq-100).

Why this matters

If you own VOO + VTI + QQQ, you look like you own three different products, but effectively you own a single concentrated portfolio: the top-20 US technology and consumer stocks. When AAPL falls 8% in a day, all three ETFs fall together. You pay three expense ratios for one correlated exposure.

True diversification requires low overlap. Adding an international ETF (VEA, VXUS), small-cap ETF (IWM), or bond ETF (BND) contributes real diversification. Adding another large-cap US ETF does not.

How to measure overlap

1. List top-10 holdings for each ETF (available on every issuer’s fact sheet or HoldLens 's /etf/ pages).
2. For each stock, record the weight in ETF A and ETF B.
3. For shared stocks, sum min(weightA, weightB) across all shared positions.
4. That sum is your weight overlap percentage.

For a more precise answer, use the full holdings list (500 for VOO, 3,700 for VTI) instead of just top-10. Top-10 overlap usually understates total overlap by 10-15 percentage points because the long tail of holdings also overlaps.

The broader lesson

“More products” is not the same as “more diversification.” Before buying another ETF, check which ETFs already in your portfolio overlap with it. If the overlap is above 50%, you’re mostly doubling up on the same exposure — at the cost of additional fees, tax-lot complexity, and a false sense of diversification.

What HoldLens tracks

/etf/ lists 12 major US ETFs with daily-disclosed top holdings sourced from each issuer’s official page. Every ticker page on HoldLens shows which tracked ETFs hold the stock (where applicable) — so you can see passive-flow exposure alongside active-manager 13F positions.

This is educational content, not investment advice. Overlap is one diversification consideration; others include sector concentration, geographic concentration, factor exposure, and correlation under stress.