One Bet Wearing Many Names: Auditing Overlap in a Multi-Fund Portfolio

A portfolio spread across nine funds, three wrappers and two platforms can feel reassuringly diversified. Yet if each of those funds holds the same handful of global technology companies, the investor has not assembled nine bets. They have assembled one bet, purchased nine times, with nine sets of charges attached. Counting funds is an exercise in administration; measuring diversification is an exercise in look-through.

The distinction matters more than it once did. Market-capitalisation indices have become increasingly concentrated, and many actively managed global funds are benchmarked against those same indices. The result is that two vehicles with quite different labels, fee levels and marketing stories may share a substantial portion of their underlying holdings. An overlap audit is the discipline of checking whether that is happening, and deciding whether it matters.

Why overlap is the default, not the exception

Diversification is often assumed to be a property of holding several things. In practice it is a property of holding things that behave differently. Two funds can be legally distinct, tax-efficient, well-run and entirely appropriate in isolation, while contributing almost nothing to one another's diversification.

Several structural forces push portfolios towards overlap:

• Shared benchmarks. A global fund and a global tracker are likely to own the same largest companies in broadly the same proportions, whatever their respective factsheets emphasise.
• Regional funds holding multinationals. A UK equity fund and a global fund may both hold the same FTSE 100 names. A European fund and a global fund may share the same large-cap industrials and pharmaceutical groups.
• Multi-asset funds. A ready-made portfolio may already contain the regional and bond exposure an investor has bought separately elsewhere.
• Manager and house concentration. An investment trust and an open-ended fund run by the same team will frequently hold near-identical portfolios.
• Share classes and wrappers. Income and accumulation units of the same fund, held in an ISA and a SIPP respectively, are one holding in substance even where they appear as two lines on a statement.

The audit, therefore, is not about catching mistakes. It is about confirming that the structure on paper matches the exposure in practice.

Gathering the look-through data

The good news is that the raw material is usually free and published. Most UK fund managers issue monthly factsheets listing the ten largest holdings. Full portfolio disclosures appear in annual and interim reports, and many providers publish complete holdings files on their websites. Exchange-traded funds typically disclose holdings daily. Platforms and research services such as Morningstar and Trustnet offer portfolio-level tools, though it is worth checking the date stamp on any data before drawing conclusions.

A workable method runs in six steps:

1. Assemble every position across every wrapper. Include the workplace pension, the SIPP, the ISA and any general investment account. Fragmentation across providers is precisely where overlap hides.
2. Collect holdings data for each fund. Where only the top ten are published, note that the remainder is unknown and treat conclusions as approximate.
3. Convert to portfolio weights. Multiply each fund's weight in the portfolio by each underlying holding's weight within that fund. A fund representing 20 per cent of the portfolio, with 6 per cent in one company, contributes 1.2 per cent of total exposure.
4. Aggregate by company. Sum the contributions. This is the number that reveals hidden concentration.
5. Aggregate again by sector, geography, currency and size band. Use a consistent classification such as ICB or GICS for sectors.
6. Compare the result with your written policy targets. Without a target, there is no basis for judging drift.

The exercise takes an afternoon for a typical portfolio and considerably less once a template exists. Repeating it annually, and after any significant purchase, is usually sufficient.

Setting thresholds that mean something

Numbers create the illusion of precision, so the thresholds below should be read as prompts for judgement rather than rules. They are, however, a reasonable starting point for a UK investor in 2026.

• Single company exposure. A look-through position above 5 per cent of the total portfolio deserves a note. Above 10 per cent, the investor should be able to explain deliberately why one company warrants that weight.
• Top ten issuers. If the ten largest underlying companies account for more than roughly a third of the portfolio, diversification is thinner than the fund count suggests.
• Fund-to-fund overlap. Two funds sharing more than half their holdings are consolidation candidates. Between 30 and 50 per cent, ask what distinct role each is performing. Below 30 per cent, overlap is generally unremarkable.
• Sector concentration. Any single sector materially above its weight in a broad global index is worth flagging. Technology has in recent years represented a quarter or more of developed-market indices, so a portfolio at 40 per cent is making a pronounced call.
• Geographic drift. If the policy target is, say, 55 per cent North American exposure and the look-through figure is 70 per cent, the portfolio has drifted. That may be acceptable, but it should be a decision rather than a by-product.
• Style and size. Check whether a supposed value fund has drifted towards quality growth, or whether two small-cap funds are fishing in the same pond.

When overlap is entirely reasonable

Not every duplicated holding requires surgery. A core-satellite structure deliberately accepts overlap in the core. Holding two managers with similar mandates can be a sensible response to governance risk, particularly where a single active manager carries meaningful stock-specific risk. Wrapper constraints sometimes make duplication unavoidable, and income and accumulation units of one fund are a bookkeeping distinction rather than an investment one.

The test is whether the overlap is chosen and understood. An investor who can say that two funds share a benchmark but differ in process, and who has sized each accordingly, is in a stronger position than one who assumed the labels implied independence.

Turning findings into action

Where the audit reveals unintended concentration, there are three responses: consolidate, resize or accept. Consolidation reduces charges and simplifies administration, but selling within a general investment account may crystallise capital gains, so it is worth using ISA and SIPP allowances where available and considering bed-and-ISA arrangements. Resizing is gentler, trimming the satellite that has quietly become the largest position. Acceptance is legitimate provided the exposure is recorded in the investment policy so that future reviews can test it.

Whichever route is taken, the audit should end in documentation. A short note recording the look-through exposure, the thresholds applied and the reasoning behind any decision converts a one-off exercise into part of the annual review cycle. That is the modest but real value of the process: not a perfect portfolio, but one whose risks are known, sized and intentional.

This article is educational and does not constitute personal financial advice.