Definition
Fund overlap is the duplication created when two or more funds hold the same securities. Hidden concentration can also arise when different holdings respond to the same sector, factor, country, or underlying company.
Overlap can be measured as shared holdings, shared portfolio weight, or the minimum of each shared position's weight. No single percentage captures each form of common risk.
Why It Matters
Owning ten ETFs is not the same as owning ten independent strategies. Broad-market, growth, and technology funds may all place large weights in the same companies. Income ETFs tied to one stock can compound exposure already held through an index fund or direct shares.
Example
A portfolio invests 50% in Fund A and 50% in Fund B. Both allocate 12% to the same company. The portfolio's company exposure is 50% × 12% + 50% × 12%, or 12%, not 6%. Fund labels did not reduce the underlying concentration.
Now add position size to the review. If a third fund is 20% of the portfolio and puts 25% in that same company, it contributes another 5 percentage points of exposure. The total company exposure becomes 17%, even though no individual ETF position exceeds 50% of the account.
How to Measure Overlap
Start with a holdings export from each fund and normalize company names and share classes. For two funds, a useful weighted-overlap measure adds the smaller portfolio weight for each shared holding. If Fund A assigns 8% to a company and Fund B assigns 5%, that company contributes 5 percentage points to the overlap score. Repeat for each shared holding.
That score answers how much of the smaller weights could be duplicated, but it is not the whole risk picture. Also compare:
- Portfolio-level weight: multiply each holding's fund weight by the fund's weight in your account, then add the results across funds.
- Sector and factor exposure: different securities can still share technology, interest-rate, value, or momentum risk.
- Options underlyings: a single-stock income ETF can add economic exposure to a company even when its holdings file mostly lists cash and derivatives.
- Holding dates: compare files from the same date so routine rebalancing does not distort the result.
Set a review threshold before looking at the answer. For example, an investor might investigate any company above 10% of the total portfolio or any pair of funds with more than 50% weighted overlap. Those are review triggers, not universal limits; the appropriate ceiling depends on the portfolio's purpose and risk tolerance.
A Three-Fund Walkthrough
The names below are real tickers; the weights are illustrative. Open each holdings file on the same date and write the top ten names in a spreadsheet.
Suppose a portfolio is 40% VOO, 40% QQQ, and 20% SCHD. VOO and QQQ both put large weights in the same mega-cap technology names. SCHD screens for quality dividend payers, so it overlaps less with QQQ, but it can still share financials or healthcare names with VOO.
For each shared company, multiply fund weight by portfolio weight, then add. If VOO is 7% in a company and QQQ is 9%, the portfolio weight is 0.40 × 7% + 0.40 × 9% = 6.4% from those two funds alone. SCHD may add more. That 6.4% is the number that belongs in a concentration log, not "I own three ETFs."
Use the in-app overlap tool on Analyze to do the same math across a whole portfolio. The point of the walkthrough is to see why ticker count is not a diversification score.
Common Mistakes
- Counting ticker symbols instead of underlying exposures.
- Checking only the top ten holdings.
- Ignoring sector, factor, issuer, and options-underlying concentration.
- Assuming a low historical correlation will remain low in a crisis.
FAQ
Is overlap always bad?
No. Intentional overlap can tilt a portfolio toward a desired company or factor. The problem is unmeasured overlap that exceeds the investor's risk limit.
How often should holdings be checked?
At least during a scheduled portfolio review and after a fund changes its index or strategy. Published holdings and weights can change between reviews.
Can two funds overlap without owning the same stocks?
Yes. A semiconductor fund and a technology index may hold different names but still respond to the same demand cycle. Bond funds with different issuers can share duration or credit risk. Review common risk drivers as well as identical holdings.
Does the overlap tool replace reading holdings?
No. It is a faster way to add the weights. You still need to know whether a shared name is a core holding, an options underlying, or a cash stub, and whether two files are from the same date.
Should I never hold two funds that overlap?
You can hold them on purpose. Write the intended tilt and a cap for the combined weight. Unmeasured overlap is the defect; a documented overweight is a choice.
