ETF Overlap Detection: Find Hidden Duplication in Your UK Portfolio

Holding three ETFs that all promise different things does not mean you own three different things. A surprising amount of UK retail money is parked in fund combinations where two thirds of the underlying holdings are the same companies, weighted at the same end of the cap spectrum. The ETF wrappers look distinct on a brokerage screen. The economic exposure underneath is not.

This article is about how to spot that duplication, why it matters for your real diversification, and what tools can do the work that a spreadsheet eventually cannot. It is written for UK investors holding ETFs across an ISA, a SIPP, or a GIA — the audience for whom this problem is most common and least visible.

This is not financial advice. Past performance does not guarantee future returns. Consider speaking to an FCA-authorised financial adviser for personalised guidance.

Why ETF overlap matters

Two reasons, and they compound.

The first is concentration risk dressed up as diversification. When you buy an "all-world" ETF and a "developed world" ETF and a "US large-cap" ETF, the marketing language sounds like you are spreading risk across geographies and styles. The actual holdings tell a different story: roughly 60 to 70 per cent of an MSCI All Country World index is US large-cap, and the top ten names of an all-world tracker are almost identical to the top ten of an S&P 500 tracker. Adding the S&P 500 fund on top is not adding diversification, it is adding weight to a position you already own. By the time you blend in a Nasdaq tracker for "tech exposure", you can end up with eight to twelve per cent of your total portfolio sitting in Apple, Microsoft, Nvidia and a handful of other names without ever having bought a single share of any of them directly.

The second is double-paying on fees. Every ETF charges an ongoing charge figure (OCF). When two of your ETFs hold the same security, you are paying both fund providers for the privilege of owning that security. In a small overlap this is negligible. Across a five-figure portfolio with three or four overlapping funds, the duplicated fee drag is a real number. It is not catastrophic — the absolute OCF difference on a typical UCITS equity ETF is single-digit basis points — but it is money you would not pay if you knew the overlap was there.

There is a third softer reason. Overlap distorts the analytical picture you have of your own portfolio. If you cannot see, at the holdings level, that 14 per cent of your wealth depends on Apple's quarterly earnings, you cannot make an informed decision about whether that is a position you want.

A worked example: VWRL plus VUSA plus VEVE

Imagine a UK investor with £30,000 split equally across three Vanguard ETFs in their Stocks and Shares ISA:

• VWRL — Vanguard FTSE All-World UCITS ETF (£10,000)
• VUSA — Vanguard S&P 500 UCITS ETF (£10,000)
• VEVE — Vanguard FTSE Developed World UCITS ETF (£10,000)

On the brokerage screen this looks like three holdings. Look at the underlying data and the picture changes.

VWRL is approximately 62 per cent US, with Apple, Microsoft, Nvidia, Amazon and Alphabet at the top of the list. VUSA is 100 per cent US large-cap S&P 500 — the same top names, just at heavier weights. VEVE is approximately 71 per cent US developed-market large-cap — again, the same top names.

The overlap maths, illustrative and rounded:

That is roughly £6,070 — about 20 per cent of the supposedly diversified portfolio — sitting in five companies. Add Meta, Berkshire Hathaway, Tesla, Eli Lilly, JPMorgan and a handful of others and you are over 30 per cent of the portfolio in fewer than fifteen names.

This is not a Vanguard problem or a UCITS problem. It is a structural feature of cap-weighted global equity indices: the largest US companies dominate the world's largest index. The investor who bought VWRL plus VUSA plus VEVE did not get more diversification by adding the second and third ETF — they doubled down on a concentration they already had.

How most UK investors miss it

Three reasons.

The brokerage UI hides it. AJ Bell, Hargreaves Lansdown, Trading 212, Vanguard's own platform — all of them list ETFs as single-line holdings. You see the ETF ticker, the unit count, the price, the unrealised P&L. You do not see what is inside. The brokerage is not trying to mislead you; it has no easy way to disaggregate a fund without licensing and ingesting holdings data, which most UK retail platforms simply do not do.

Fund factsheets disclose only the top ten. Every UCITS ETF publishes a Key Information Document and a monthly factsheet. Both list the top ten holdings. Both stop there. Two ETFs with very different "top ten" tables can still overlap heavily if you compare them at position 11 to position 200, where most of the index sits. JustETF, Trustnet and Morningstar UK display this top-ten data clearly and helpfully, and most investors stop there. That is enough to spot blatant overlap (an FTSE 100 tracker plus a UK income fund will obviously share names) but it is not enough to spot the subtler 200-position overlap inside global trackers.

Wrapper splitting hides the total. A UK investor with the same set of ETFs split across an ISA and a SIPP at different brokers cannot see them on one screen at all. They have to mentally aggregate two accounts before they can even start comparing the funds. Most do not bother.

The result is that ETF overlap is the single most common analytical blind spot in UK retail portfolios. It is not a sign of bad investing — it is a sign of the data not being readily available.

Manual detection in Excel — and why it breaks

You can do this by hand. People do. Here is the rough process.

1. Download the full holdings file for each ETF — usually a CSV or XLSX from the fund provider's website. iShares and Vanguard publish these monthly, lagging by about two weeks.
2. Standardise the security identifiers across files. ISIN is the most reliable; tickers and company names will not match across providers because of share-class differences and naming conventions ("Alphabet Inc Class A" vs "Alphabet A").
3. Multiply each holding's weight by the value you hold in that ETF, to produce a £-denominated exposure.
4. Pivot or SUMIF across all three sheets to aggregate by ISIN.
5. Sort by combined £ exposure to find your real top names.

This works. It takes most people a couple of hours the first time. The reason it does not survive contact with reality is that step 1 has to be repeated every month — fund holdings change as the index rebalances and as new money flows in — and step 2 is a maintenance trap. ISINs are usually clean, but corporate actions (spin-offs, mergers, share-class consolidations) introduce edge cases. Tesla's listing changes, Alphabet's two share classes, the LSEG/Refinitiv merger, the post-Brexit relisting of certain dual-listed names — every few months something happens that breaks last month's spreadsheet.

The deeper problem is that the spreadsheet shows you a snapshot. It does not warn you when the picture has shifted. If VWRL rebalances and Nvidia's weight jumps from 3.6 per cent to 4.4 per cent, your spreadsheet will not tell you unless you re-download all three holdings files and rerun the pivot. Most people do this once, congratulate themselves, and never do it again.

What "look-through" means at the holdings level

"Look-through" is the term for analysing a portfolio at the level of underlying securities rather than at the wrapper level. Instead of saying "I own £10,000 of VWRL", a look-through view says "I own £442 of Apple, £394 of Microsoft, £358 of Nvidia, £216 of Amazon, £241 of Alphabet, £104 of Meta, …" and so on across all 3,500-odd constituent positions.

Done across multiple ETFs it produces an aggregated holdings ledger — the actual companies you own, weighted by your real cash exposure to each, regardless of which fund they came from. That is the analytical object you need to answer overlap questions properly.

A useful look-through implementation has three properties:

1. Aggregation across wrappers. It combines an ISA, a SIPP and a GIA into one view, so the question "how much Apple do I own across everything?" has a single answer.
2. Refreshed holdings data. Funds rebalance monthly. The look-through view should reflect that without you having to redo the spreadsheet.
3. Concentration surfacing. It is not enough to expose the data. The tool should tell you when a single name has crept above a threshold — five per cent, ten per cent — that you have decided is the limit of your comfort.

Tools for ETF overlap, fairly compared

A small market exists for this. The serious options for a UK investor are roughly:

The honest take: if you only ever want to check two ETFs against each other to settle a single question, ETF Insider is free and quick. If you want to keep an ongoing view of overlap across your real, multi-wrapper UK portfolio without redoing a spreadsheet every month, you need something with portfolio aggregation and refreshed holdings — Sharesight does the aggregation but not the look-through, JustETF does some of both but stops short of true wrapper-level analysis, and Invormed is built for the specific intersection.

Why UCITS structure makes this harder in the UK

The UCITS regulatory framework, which governs almost every ETF a UK retail investor will buy, has a quirk relevant to overlap detection.

UCITS ETFs are domiciled in Ireland or Luxembourg and report holdings on a different cadence and through different filings than the underlying US-listed sister fund. VWRL (the UCITS All-World tracker) and VT (the US-listed All-World tracker) hold very similar portfolios but you cannot use the US fund's holdings file to analyse the UK one — the cash positions, FX hedging overlay, and small synthetic exposures differ. UK retail investors who pull data from US sources sometimes end up analysing the wrong fund.

The other UCITS quirk is share-class proliferation. The same fund — say, Vanguard FTSE All-World — exists as VWRL (distributing, GBP), VWRP (accumulating, GBP), VWCE (accumulating, EUR) and several others. They hold the same underlying basket but trade as different ISINs. A look-through tool needs to recognise that VWRL and VWRP overlap 100 per cent at the security level even though they are different tradeable instruments. This is the kind of edge case that catches manual spreadsheets and that a purpose-built tool should handle silently.

What to actually do with this

Three practical steps, in increasing depth.

1. Run a one-off check. Pick the two largest ETFs in your portfolio and run them through ETF Insider or a similar overlap checker. If the overlap is over 50 per cent, that is information worth having. Below 25 per cent, the funds are doing meaningfully different things.
2. Aggregate across wrappers. Pull a holdings export for each broker account you have. Put them in one place — even if it is a single Google Sheet. The point is to stop thinking about the ISA and the SIPP as separate portfolios for analytical purposes; they are one portfolio for overlap and concentration.
3. Decide on a concentration limit. "No single underlying name above five per cent of the total" or "no single sector above 30 per cent" — pick a rule. Then check whether your current portfolio breaks it. Most UK investors holding three or more global trackers find they break a five-per-cent rule on Apple or Microsoft. Whether to act on that is a personal decision; knowing it is a precondition.

None of this is about avoiding ETFs. ETFs remain the cleanest, cheapest way for most UK retail investors to access broad markets. The point is that "I own three ETFs, so I am diversified" is a statement that is true at the wrapper level and frequently false at the holdings level — and the gap between the two is where surprises live.

Frequently asked questions

What is ETF overlap?

ETF overlap is the proportion of underlying holdings shared between two or more funds you hold. If VWRL and VUSA both hold Apple at meaningful weights, that Apple position is "overlapping" — your real exposure to Apple is the sum of both ETFs' weights, not just one. Overlap is measured at the security level (usually by ISIN) and expressed as a percentage of the smaller fund's weights that also appear in the larger one.

How much overlap is too much?

There is no fixed rule, but a useful rough framework: under 25 per cent overlap, the funds are doing genuinely different things. Between 25 and 50 per cent, you are paying twice for some exposure but still getting differentiation. Over 50 per cent, the second fund is largely a duplicate of the first and you should ask whether you actually want a second copy or whether one fund plus a satellite holding would do the same job at lower cost. Over 70 per cent, the funds are functionally interchangeable.

Does Sharesight show ETF overlap?

No. Sharesight tracks ETFs as single line-item holdings and does not disaggregate them into underlying securities. It is excellent at performance and tax reporting at the wrapper level, but it does not produce a look-through view of overlap or concentration at the stock level. For overlap analysis you need a tool that ingests fund holdings data — either a dedicated overlap checker, JustETF's portfolio tools, or Invormed's built-in look-through.

How do I check overlap between Vanguard ETFs?

The quickest way is to download the full holdings file from Vanguard's UK site for each fund — they are published monthly as XLSX or CSV — and compare them by ISIN in a spreadsheet. The faster way is to use a free overlap checker like ETF Insider, paste in the two tickers, and get the percentage in seconds. Vanguard's own UK platform does not surface overlap directly between its funds, which is a recurring complaint on UK investing forums.

Are sector ETFs less overlapped than world ETFs?

Usually, yes. A US technology sector ETF and a US healthcare sector ETF have near-zero overlap by construction — they hold different parts of the market. The trap is combining a world tracker with a sector ETF: a technology sector fund will typically sit inside the world tracker as well, so the satellite "overweight" is actually a "double overweight". Sector ETFs are most useful when paired with a world tracker that has been deliberately under-weighted in that sector, not as additions on top.

What is the cheapest tool for UK ETF overlap?

ETF Insider is free for two-fund comparisons and covers most UCITS ETFs a UK investor would hold. JustETF's portfolio tools are free at the basic tier and provide some overlap visibility for ETFs listed on UK and European exchanges. For ongoing portfolio-level overlap across multiple wrappers, free tools quickly run out of road — that is where a paid portfolio intelligence tool starts to earn its keep, but for a one-off check you do not need to spend anything.

Want to see your real holdings, not just your fund tickers?

Invormed aggregates your ISA, SIPP and GIA, looks through every ETF, and tells you the actual companies and weights underneath. We are in early access — join the early-access waitlist and we will let you in as we open up.