What Is ETF Overlap? How to Check It and How Much Is Too Much

ETF overlap is the percentage of two funds' portfolios that is invested in the same underlying stocks. It matters because owning several overlapping funds concentrates your portfolio invisibly: your brokerage statement shows three or four tidy ticker symbols, while underneath, the same handful of mega-cap stocks may dominate all of them.

How is ETF overlap measured?

The standard measure is overlap by weight: for every stock held by both funds, take the smaller of its two portfolio weights, then add those minimums up. If Apple is 7% of fund A and 6% of fund B, Apple contributes 6 percentage points of overlap. Summed across every shared holding, this tells you what fraction of your money is effectively invested identically in both funds.

Counting shared names alone overstates the difference between funds. Two S&P 500 funds from different issuers hold essentially the same 500 stocks at essentially the same weights — nearly 100% overlap by any measure. But a total-market fund holds thousands of stocks an S&P 500 fund doesn't, and still overlaps it heavily by weight, because the S&P 500 mega-caps dominate both. Weight, not name count, is what determines how the pair behaves.

How much do popular ETF pairs actually overlap?

Computed from each fund's full issuer-published constituent list (holdings as of mid-2026 — see the live pages for current figures):

Pair	Overlap by weight	What it means
SPY vs VOO	~95%	Same index, different issuer — pick one
VOO vs VTI	~88%	Total market ≈ S&P 500 plus a small-cap sliver
VGT vs XLK	~79%	Two tech sector funds, heavily redundant
VTV vs VUG	~3%	Value and growth — genuinely complementary

Every pair page shows the top shared holdings with each fund's exact weights, where the sector exposures differ, and the constituent coverage behind the numbers. Browse all pairs on the ETF overlap hub.

How much overlap is too much?

There is no single threshold, but the useful question is: what job did you hire the second fund to do?

• Above ~70% overlap, the funds are close substitutes. Holding both adds no diversification — it adds duplication, plus a second expense ratio and more positions to track. This is usually an accident (a 401(k) S&P 500 fund plus a personal VOO position, say), not a strategy.
• Between roughly 40% and 70%, a meaningful share of your money is invested identically in both funds. That can still be fine — VTI holders often accept near-90% overlap with VOO because the total-market fund's small-cap tail is the point — but you should know the shared core counts against you twice in a downturn.
• Below ~15%, the funds hold genuinely distinct baskets, and pairing them actually spreads your exposure.

The real danger isn't any single pair — it's stacking. Three funds can each look reasonable against the others pairwise while all three load up on the same ten mega-caps. Apple held directly, inside an S&P 500 fund, and inside a tech sector fund is one exposure wearing three costumes.

How do I check ETF overlap in my own portfolio?

For a single pair, use an overlap checker that publishes the underlying numbers — shared holdings, weights in each fund, and data coverage — rather than a bare percentage. The PortLens overlap pages show all of this, computed from full issuer constituent lists (methodology documented here).

For a whole portfolio, pairwise checks aren't enough, because stacking hides between the pairs. A portfolio-level look-through explodes every fund into its constituents, sums your exposure to each underlying company across every position, and reports your true concentration: effective number of holdings, top-10 underlying weight, and which stocks appear in multiple funds. That's what a free PortLens scan computes for your actual holdings — no account required.

Key takeaways

• ETF overlap is the share of two funds' weight invested in the same stocks; measure it by weight, not by counting shared names.
• Twin index funds (SPY/VOO) overlap ~95% — own one, not both. Broad pairings like VOO/VTI overlap ~88%, which is acceptable if the non-overlapping tail is deliberate.
• Style splits (value vs growth) genuinely diversify; duplicate sector funds don't.
• Portfolio-level stacking is the failure mode pairwise checks miss — look through everything at once before adding a new fund.

This article is for information and education only and is not investment advice. Analytics referenced are computed as described in our methodology; see our disclosures.