Seven pairs of funds people actually hold, measured against each other from the holdings each issuer publishes, with the two numbers that answer different questions.
Dan Mercer··9 min read
Holding four funds feels like four decisions. Most of the time it is one decision and three copies of it, and you do not have to take anybody's word for that, because every fund publishes exactly what it holds. Here is the overlap between the seven pairs people most often end up owning, read off the issuers' own holdings files, with a stated verdict at the end of each one.
· press to enlargeIn this post↓
The advice people are given about funds is to diversify, and the way most of us act on it is to buy a second one. Then a third, because it is about technology, and a fourth, because it is about growth. Four tickers feels like four decisions.
Every one of those funds publishes exactly what it holds, in a fund holdings file its issuer updates on a fixed schedule. So this is not a question anybody has to have an opinion about: you can add up the companies two funds have in common and read the answer off. I did that for the seven pairs people most often end up holding, and the arithmetic is not what the folk wisdom says.
01
Do VOO and VTI overlap?
The most common two-fund portfolio in the world is an S&P 500 index fund next to a total stock market fund. VOO tracks the 500 largest US companies; VTI tracks essentially every listed US company. Different indexes, different names, and the usual reason given for holding both is that the second adds the smaller companies the first leaves out.
That is the screen at the top of this post, and it is worth pressing to read full size. Of VOO’s published weight, 99.87% sits in companies VTI also holds. Of VTI’s, 90.32% sits in companies VOO holds. 500 companies are in both, out of VOO’s 503 and VTI’s 3,457.
Read those two percentages as a pair, because the gap between them is the whole finding. The small fund sits inside the large one almost completely. The large one is only mostly the small one. Both are true at once and a single blended number cannot say either.
VTI holds 2,957 companies that VOO does not, and together they are under a tenth of it.
Almost entirely, in the direction that matters to somebody holding both: 99.87% of VOO is inside VTI.
VTI holds nearly seven times as many companies, and that sounds like a different fund. By weight it is not: 88.60% of a portfolio built from either one is identical exposure. The 2,957 extra companies are real, and together they are a tenth of the fund.
02
Why are there two different overlap numbers?
Most ETF overlap tools report one figure. Two funds are “70% overlapping”, and it is never quite clear 70% of what. There are two honest measures of portfolio overlap here and they answer different questions.
How much of this fund is inside that one. Each fund’s own weight sitting in companies the other also holds, measured against that fund’s own total. Asymmetrical, and the one to read when deciding whether a fund you hold is already covered by another.
How much identical exposure you would be buying twice. For every company both hold, the smaller of the two weights, added up. Symmetrical, and the one to read when asking what a portfolio built from either would actually own.
The same companies, weighted differently by each fund. Identical exposure is the sum of the smaller number in each row, which is why it is lower than either fund's own share. · press to enlarge
Nvidia is 8.08% of VOO and 6.87% of VTI. Hold either fund and 6.87 points of it are the same company at the same weight. VOO’s extra 1.21 points are not doubled up with anything, which is why identical exposure across the whole pair comes out at 88.60% rather than at 100%.
One caveat the page states and I will repeat: every percentage is measured against each fund’s own published total, not against 100. Issuers round, and cash and futures rows cannot be attributed to a company, so a published basket routinely sums to somewhere in the nineties. Measuring against 100 would quietly understate every figure here.
The read: Not a signal
Because two different questions are being asked, and the useful one is not symmetrical.
Sharing a company is not the same as sharing exposure to it. VOO gives Nvidia 8.08% and VTI gives it 6.87%, so 6.87 points of the two are the same bet and VOO's extra 1.21 is not shared with anything. Adding the weights would claim 14.95 points of a company that is at most 8.08 in either fund.
03
Is SPY the same fund as VOO?
Worth doing the trivial case first, because it calibrates everything after it. SPY and VOO both track the S&P 500. Two issuers, two tickers, one index.
Same index, two tickers. SPY as of 14 September 2026 and VOO as of 31 August 2026, which is where most of the missing 2.2 points comes from. · press to enlarge
100.00% in both directions, 503 companies in both, and 97.80% identical exposure. The gap from 100 is not a disagreement about what to own. These two baskets were published a fortnight apart, and an index fund rebalances in between.
So when these two funds are compared, it is about cost and structure rather than holdings. That is a real comparison and it is not this one.
The read: Not a signal
The same 503 companies, and 97.80% the same exposure. The difference is not what is inside.
Every company in one is in the other. The 2.2 points that are not identical are rounding and a few days of drift between when each issuer published, not a different view of the market. Whatever separates these two funds, it is not their holdings.
04
Does QQQ add anything to an S&P 500 fund?
This is the pair where the two measures pull hardest in opposite directions, and reading only one of them produces a confident wrong answer in either direction.
QQQ's 100 companies are almost all already in VOO, yet only about half of a portfolio built from either is the same exposure. Holdings as published: QQQ as of 30 June 2026, VOO as of 31 August 2026. · press to enlarge
87 of QQQ’s 100 companies are in VOO, and they are 95.64% of QQQ by weight. Somebody buying QQQ alongside an S&P 500 fund to get exposure to companies they do not have is buying thirteen companies they did not already own.
But identical exposure is only 51.88%. QQQ holds a hundred companies where VOO holds 503, so the same names carry much heavier weights. That is a real change to a portfolio. The honest description is not “QQQ is redundant” and not “QQQ diversifies you”. It is that QQQ is a bet on the same companies, sized differently.
Which of those two readings matters depends on what somebody thought they were buying, and that is worth knowing before rather than after. If the reason was “more technology”, the weights say yes. If it was “something my index fund does not cover”, the holdings say almost no.
Almost no new companies, and a genuinely different portfolio. Both halves of that are the point.
95.64% of QQQ sits in companies VOO already holds, so as a way of owning something new it adds close to nothing. Identical exposure is only 51.88%, because QQQ concentrates the same companies far harder. Holding both is not diversification; it is a decision to weight what you already own differently, which may be exactly what somebody wants.
05
What about a sector fund like XLK?
The sector funds are where I expected the clearest result, and it is cleaner than I expected.
XLK holds 73 companies and VOO holds 503. Every single one of the 73 is in VOO. VOO as of 31 August 2026, XLK as of 14 September 2026. · press to enlarge
100.00% of XLK sits in companies VOO also holds, across 73 companies. That figure is not approximately a hundred; it is a hundred, because the S&P 500 technology sector fund holds the technology companies in the S&P 500.
This one is worth being precise about, because “adds nothing” would be the wrong summary. It adds no company and it changes a great deal of weight: 37.85% of VOO is in those same 73 companies, so buying XLK beside VOO concentrates a third of the index into the whole of a second position. That is a deliberate thing to do. It is just not diversification, and the word on the label does not say which it is.
The read: Worth watching
100.00% of XLK is inside VOO. A sector fund of this kind adds no company at all.
Every one of XLK's 73 holdings is already in the S&P 500 fund, because XLK is a slice of the same index rather than a separate universe. What it changes is weight, and only weight. A reader who bought it expecting exposure to technology companies they did not own has bought none.
06
Does splitting into growth and value split anything?
Growth and value are the pair I was least sure about before running it, and the answer needs three comparisons rather than one, because the finding is the relationship between them.
The growth fund, against the S&P 500 fund. VUG holds 146 companies and 97.56% of its weight is inside VOO. · press to enlargeThe value fund, against the same S&P 500 fund. VTV holds 306 companies and 98.72% of its weight is inside VOO. · press to enlarge
Separately, each looks like every other result in this post: 97.56% of VUG and 98.72% of VTV sit inside VOO. Neither is a source of companies an index fund does not have. Then compare the two with each other.
The same two funds against each other: 21 companies in common, and 3.26% identical exposure. Both baskets as of 31 August 2026. · press to enlarge
3.26%, over 21 companies. Two funds that are each almost entirely inside a third fund, and almost entirely outside each other. That is exactly what a real split looks like: the index is being cut in two, and the halves are nearly disjoint because a company is sorted into one bucket or the other.
So the rule is not “style funds are redundant”. Holding VUG and VTV together reconstructs something close to the index. Holding VUG beside the index does not split anything; it tilts the same holdings. Which of the two somebody has done is a question about their other positions, not about the fund.
The read: Reassuring
Yes, and it is the only split here that genuinely divides the index. VTV and VUG share 3.26% with each other.
Each of the two sits almost entirely inside the S&P 500 fund, at 98.72% and 97.56%, so neither adds companies to it. Against each other they are nearly disjoint. Slicing an index in two really does produce two different things; buying one slice alongside the whole index does not.
07
What does a genuinely different second fund look like?
Every figure above is easier to judge with a control, and this is it: a US total market fund against the same issuer’s international one.
Two funds of roughly the same size with almost nothing in common: 58 shared companies and 0.99% identical exposure. Both as of 31 August 2026. · press to enlarge
0.99% identical exposure, and 58 companies in common out of about 3,450 each. Set that beside VOO and VTI at 88.60% and the difference is not a matter of degree.
I am not going to tell you to own it, and this post is not a view on international equities. What the number settles is narrower and more useful: when a second fund really is a different fund, the overlap measure says so loudly, which is the reason to trust it when it says the opposite.
The read: Reassuring
Under one point of identical exposure. This is the comparison every pair above was being measured against.
VTI and VXUS hold 58 companies in common out of roughly 3,450 each, and 0.99% of a portfolio built from either is the same exposure. Nothing else in this post comes close. Whatever the two funds do for a portfolio, they are not the same fund with a different label.
08
How do I check this against what I already hold?
Everything above compares two funds. The question underneath it is usually about a specific portfolio, and the last thing on a fund page answers that without an account and without sending anything anywhere.
Type any tickers you hold directly. The answer is computed in the browser from the basket the page already loaded, and nothing you type is sent anywhere. · press to enlarge
Three companies, one fund, 10.62%. Nvidia alone is 8.08% of VOO, so anybody holding Nvidia shares and an S&P 500 fund holds Nvidia twice, and the fund half is larger than most people picture.
Every fund page also ranks the other funds most worth checking against it, and it is the same measure the rest of this post used, so the number here should already look familiar.
Ranked by identical exposure, which is why SPY sits above VTI despite VTI's higher share of VOO. VTI's line reads 99.87% and 500 companies, the same two figures step 1 opened with. · press to enlarge
VTI is the third fund on that list, at 99.87% and 500 companies in both, exactly what step 1 found comparing the two directly. That agreement is not a coincidence to be reassured by; it is the same arithmetic run from two different pages, which is the whole reason a figure on this product is checkable rather than asserted.
That is where a holdings file stops being able to help. It reports what is in the basket. Whether owning a company at that weight is right for somebody is a question about their own plan, and nothing in a published basket answers it. The same boundary the rest of this product holds to: the document says what it says, and the decision is not in the document.
If you want the company-level version of this for something you hold, that is the method in how I read a company in thirty minutes; for who else owns it and how much it matters to them, the quarterly filings are the subject of how to read a 13F filing.
Three things I would take from an afternoon of this.
Two percentages, not one. A fund can sit almost entirely inside another while being only a slice of it, and one number cannot say both.
Sharing companies and sharing exposure are different. QQQ is 95.64% inside VOO by holdings and 51.88% by identical exposure, and both facts are about the same pair.
A basket has an as-of date. Every figure in this post moves when an issuer publishes again, which is why the comparison pages state the date and why the method is the part worth keeping.
Nothing above is a recommendation to buy or sell any of these funds. It is arithmetic over lists the issuers publish, and the useful outcome is knowing what you own rather than being told what to do about it. If you would rather not keep typing tickers, an account keeps the list and checks every fund at once.
The read: Not a signal
Three companies and one fund was enough to find 10.62% of it already held directly.
A holdings file can tell you what you own twice and cannot tell you whether that is a problem. Somebody holding Nvidia directly and VOO as their index fund owns Nvidia at 8.08% of the fund on top of the shares in their own name. Whether they want that is a question about their plan, not about the basket.
Questions
What is ETF overlap?
ETF overlap is the share of two funds that is the same underlying companies. It is measured two ways: how much of one fund's weight sits in companies the other also holds, which is different in each direction, and identical exposure, which sums the smaller of the two weights for every company both hold and is the same number either way round.
Do VOO and VTI overlap?
Yes, almost entirely. 99.87% of VOO's published weight is in companies VTI also holds, 90.32% of VTI's is in companies VOO holds, and 88.60% of a portfolio built from either is identical exposure, measured on the issuers' holdings files as of 31 August 2026.
Does QQQ overlap with the S&P 500?
QQQ holds 87 of its 100 companies in common with the VOO S&P 500 fund, which is 95.64% of QQQ by weight. Identical exposure between them is 51.88%, because QQQ spreads the same companies across a hundred positions rather than 503 and so weights each of them much more heavily.
How do I check the overlap between two ETFs?
Open /compare/funds/ followed by the two tickers on Investailor, for example /compare/funds/VOO/VTI. The page reports both directions, the number of companies in both and the identical exposure, computed from each issuer's own published holdings file, and it needs no account.
Is owning two overlapping ETFs a problem?
That depends on what the second fund was bought for, which a holdings file cannot tell you. What the file does settle is what is actually owned: whether a second fund adds companies, and whether it changes how heavily the shared ones are weighted. This post reports those figures and stops there, because the rest is a question about somebody's own plan.
Is any of this investment advice?
No. Everything here is arithmetic over holdings the fund issuers publish, and the post makes no recommendation about any fund it names and no forecast about any of them.
Sources
Every figure above was read off the product, and comes from the documents below. Where a figure is not in a filing, the post says so rather than estimating one.
Nothing here is investment advice, and the post makes no forecast about any company or fund it names.
Builds Investailor, a research desk that reads SEC filings, 13F holdings reports, Form 4 insider transactions and ETF holdings files, and traces every figure it shows back to the document it came from.
Writes each post by working through the real filing in public: every number in a walkthrough is read off a page the reader can open, and the primary documents are linked at the foot of the post.
Publishes the method rather than the conclusion. These posts say what a filing records, what it leaves out, and where the evidence stops, and they carry no price targets, ratings or forecasts.
Do this for everything you hold, not three tickers at a time
Hold the funds and the companies in one place
Add what you actually own, funds included, and see it as one portfolio rather than a page you check per ticker. The free plan does not expire and asks for no card.
Check every fund at once, not one at a time
Step 8's check answers for three typed tickers against one fund. This is the same question run over your whole portfolio and every fund in it together, so a company held through four funds shows up once, added up.
Under each company you hold indirectly, which fund brought it in and how much of it, so a company you already own comes with an answer to what brought it there.
