Before ETFs became widely available, and still today across many workplace pensions and platform fund ranges, the two dominant fund structures in the UK were the OEIC (Open-Ended Investment Company) and the unit trust. Both remain enormously popular, and both do broadly the same job — pooling investor money into a diversified portfolio — but they are built on different legal foundations. This article explains the practical difference, which matters less for day-to-day investing than it once did, but is still worth understanding.
What both structures have in common
OEICs and unit trusts are both "open-ended" funds, meaning the fund can create new shares or units when investors put money in, and cancel them when investors withdraw money, so the fund's total size expands and contracts to match investor demand. This is a key contrast with closed-ended structures like investment trusts, which have a fixed number of shares traded on a stock exchange. Both OEICs and unit trusts are typically priced once a day, based on the value of their underlying holdings at a set valuation point.
The unit trust structure
A unit trust is established under trust law. Investors' money is held by a trustee (usually a large financial institution independent of the fund manager) on behalf of investors, who own "units" representing a proportional share of the trust's assets. The fund manager makes the investment decisions, while the trustee has an oversight role, holding the assets and monitoring the manager's compliance with the fund's stated objectives and regulatory rules.
Pricing structure
Historically, unit trusts used "dual pricing", with a separate bid price (for selling units) and offer price (for buying units), creating a spread similar to how shares trade — though many unit trusts have since moved towards single, "swinging" pricing more similar to OEICs.
The OEIC structure
An OEIC is structured as a company (an "investment company with variable capital"), with investors owning shares in that company rather than units in a trust. Instead of a trustee, an OEIC has a "depositary" performing a broadly similar oversight role — safeguarding assets and monitoring the fund's operator.
Single pricing
OEICs generally use single pricing, meaning there is one price at which investors buy and sell shares on a given valuation day, which many investors find simpler to understand than the historical dual-pricing approach used by some unit trusts.
Sub-funds under one umbrella
OEICs are often structured as an "umbrella company" containing multiple sub-funds (for example, a UK equity sub-fund, a global bond sub-fund, and a multi-asset sub-fund), each with its own investment objective, sharing the same overarching legal and administrative structure, which can create some efficiencies for the fund provider.
Comparing OEICs and unit trusts
| Feature | Unit trust | OEIC |
|---|---|---|
| Legal basis | Trust law | Company law |
| What investors own | Units in a trust | Shares in a company |
| Oversight body | Trustee | Depositary |
| Pricing | Historically dual-priced, though many have moved to single pricing | Single priced |
| Structure | Typically a standalone trust | Often an umbrella with multiple sub-funds |
| Practical difference for investors today | Minimal for most day-to-day purposes | Minimal for most day-to-day purposes |
Why the distinction matters less than it used to
For most UK retail investors buying funds through a modern investment platform, ISA, or SIPP, the practical experience of holding a unit trust versus an OEIC is very similar: both are dealt once a day at a single valuation point in most modern cases, both are regulated under broadly the same UK and (historically) EU-derived rules, and both provide diversified exposure to whatever underlying assets the fund holds. Many fund managers today run their fund ranges predominantly as OEICs, having converted older unit trusts over time, partly reflecting this convergence.
What still matters more, in practice
For most investors, factors such as the fund's underlying holdings, its investment objective, its ongoing charges figure, whether it is actively or passively managed, and the strength of its oversight arrangements matter considerably more day-to-day than whether it happens to be legally structured as a unit trust or an OEIC.
How OEICs and unit trusts differ from ETFs and investment trusts
Both OEICs and unit trusts are open-ended and priced once daily, in contrast to ETFs (which are exchange-traded, priced continuously through the day) and investment trusts (which are closed-ended, with a fixed number of shares traded on an exchange, sometimes at a discount or premium to net asset value). All four structures can, in principle, be used to hold similar underlying assets — the difference lies mainly in how they are bought, sold, and priced.
A worked example: dealing in a unit trust versus an OEIC
Suppose a hypothetical investor wants to invest £5,000 in a UK equity income fund, available as both a unit trust and an OEIC share class from the same provider. In both cases, the investor's order is typically collected before a daily cut-off time (commonly midday) and dealt at the next valuation point, using the same underlying portfolio of shares. If the unit trust uses swinging single pricing and the OEIC also uses single pricing, the investor might see a very similar or even identical price on both structures on the same day, since they may hold near-identical, or in some cases entirely identical, underlying portfolios managed by the same team. The main visible difference to the investor would likely be paperwork terminology — "units" versus "shares" — rather than anything affecting the investment outcome itself. This example is illustrative only.
Practical considerations when choosing between fund structures
- Focus primarily on the underlying investment strategy, objective, and holdings, rather than the legal wrapper (unit trust or OEIC).
- Compare ongoing charges figures and any other fees between share classes, which can sometimes differ even within the same underlying fund.
- Check the fund's KIID/KID and factsheet, which will state its legal structure alongside its objective, risk rating, and charges.
- Consider whether a platform offers both structures for a fund of interest, since not every provider or platform lists every share class.
How historical regulation shaped these structures
Unit trusts have existed in the UK since the 1930s, making them one of the country's oldest pooled investment structures, established under trust law that predates modern company-based fund regulation. OEICs were introduced considerably later, in the late 1990s, as UK regulation moved to align more closely with fund structures used elsewhere in Europe, offering fund groups a company-based alternative that many found administratively simpler, particularly for running multiple sub-funds under a single umbrella structure. This history explains why many older, well-established UK funds were originally launched as unit trusts, while newer fund launches over the past two decades have more often used the OEIC structure.
Conversions from unit trust to OEIC
Many fund management groups have, over time, converted their existing unit trusts into OEICs, partly for administrative efficiency and partly to align their full fund range under a single consistent structure. Where this happens, investors are typically informed in advance and the underlying investment strategy and objective usually remain unchanged, with the conversion affecting the legal wrapper rather than what the fund actually invests in.
What the depositary and trustee actually check
Both the depositary (for OEICs) and the trustee (for unit trusts) perform a similar core function: independently verifying that the fund manager is operating within the fund's stated investment objective and regulatory limits, safe-keeping or overseeing safe-keeping of the fund's assets, and ensuring that units or shares are correctly priced and that investor money is handled properly. This independent oversight function is a structural safeguard present in both fund types, distinct from any protection relating to investment performance itself — neither a depositary nor a trustee can prevent a fund's underlying investments from falling in value, since that is a normal market risk inherent in any fund investment.
Reading a fund's full name to identify its structure
A fund's official name, as shown on its factsheet and KIID/KID, will typically state its legal structure explicitly — for example, "XYZ Global Equity Fund, a sub-fund of XYZ Investment Funds ICVC" indicates an OEIC structure (ICVC stands for Investment Company with Variable Capital), while a name referencing a "unit trust" in its formal title indicates the older structure. Platforms do not always display this full formal name in search results or account summaries, so checking the underlying factsheet or Key Investor Information Document remains the most reliable way to confirm a specific fund's legal structure, if this detail matters for an investor's own record-keeping.
Share classes within either structure
Both OEICs and unit trusts commonly offer multiple share classes of the same underlying fund, differing by factors such as accumulating versus income, currency of denomination, or the level of ongoing charge (with lower-cost "clean" share classes now standard on most modern platforms, following historical regulatory changes that removed commission payments previously built into some older share classes). Checking which specific share class is held, and its associated ongoing charges figure, is worth doing regardless of whether the underlying fund is a unit trust or an OEIC.
A final practical note
For the overwhelming majority of UK retail investors, the decision of which specific fund to hold will rarely, if ever, hinge on whether it happens to be a unit trust or an OEIC. It is included here as background context precisely because the terminology appears so frequently across fund literature, platforms, and pension documentation, and understanding it removes one small source of confusion when reading about funds generally.
Key takeaways
- OEICs and unit trusts are both open-ended fund structures, expanding and contracting in size as investors buy and sell.
- Unit trusts are based on trust law with a trustee overseeing assets; OEICs are structured as companies with a depositary performing a similar role.
- Unit trusts have historically used dual pricing, though many now use single pricing similar to OEICs, narrowing the practical difference.
- For most investors today, the underlying investment strategy and charges matter far more than whether a fund is legally a unit trust or an OEIC.
- Both structures differ from ETFs (exchange-traded, priced continuously) and investment trusts (closed-ended, traded at a discount or premium to net asset value).