Money market funds explained

A money market fund is a type of investment fund that holds cash and short-term, low-risk assets such as government bonds. Its purpose is to give a return that is slightly higher than what you can get from cash at the bank, after fees¹. It is a place to hold money rather than grow it, and it is designed to be low risk, but it is not a savings account: the value of your holding can fall, and the return is an aim, not a guarantee².

In UK law, a money market fund means a fund authorised under Article 4 or Article 5 of the EU Money Market Funds Regulation of 14 June 2017³. In everyday terms, it is a pooled fund: lots of investors' money is collected and managed by a professional fund manager who invests it across a range of assets⁴. This page explains what these funds hold, how they are priced, what they cost, how they behave inside an ISA or pension, and how they compare with an ordinary savings account.

What a money market fund is and what it holds

A money market fund is a fund, which means it is a collection of lots of different people's money, managed by a professional fund manager who invests it across a range of different assets⁷. What marks it out from other funds is what it buys: money market funds invest in low-risk and short-term assets, including cash and government bonds⁴. Because the assets are short-term, there is less uncertainty about what they will be worth when they mature, which is what makes the fund stable compared with funds that buy shares or long-dated bonds².

The legal definition matters for ISA rules, and it is precise: a money market fund is one authorised in accordance with Article 4 or Article 5 of Regulation 2017/1131 of the European Parliament and of the Council of 14 June 2017 on Money Market Funds³. Those two articles cover the two main types of authorised money market fund. For a consumer, the practical point is that only funds authorised in this way count as money market funds for tax-wrapper purposes, so a fund that merely holds cash-like assets is not automatically one.

Because it is a pooled fund, a money market fund gives you a stake in a spread of holdings rather than a single deposit with one institution. Funds in general offer this diversification: your money is spread across a number of different investments, and the management and admin costs are shared among all the investors in the fund⁸. In a money market fund that spread sits at the safest end of the market: cash, government debt and other short-term instruments, rather than company shares.

The aim: a return slightly above bank cash

A money market fund does not aim to make your money grow the way a share fund does. Its purpose is to give a return that is slightly higher than what you can get from cash at the bank, after fees¹. Another way fund managers describe it: these funds typically aim to provide a cash-like level of return, although this can vary between funds, and each fund's specific aims are recorded in its Key Investor Information Document (KIID)⁹.

Because they invest in a portfolio of short-term securities, money market funds offer a relatively high level of liquidity at a relatively low level of risk⁹. That combination is the product's whole proposition: quick access, low volatility, and a modest return. Fund managers describe it as a low-risk investment that gives you a place to hold rather than grow your savings, while aiming to give you a slightly higher return than cash².

Who these funds tend to suit is set out by providers in similar terms: investors with short-term goals, or those looking to lower the overall risk of their investment portfolio. The same guidance notes they may not be suitable for longer-term investment needs⁹. The reason is arithmetic rather than opinion: a fund aiming only slightly above bank cash is unlikely to keep pace with the long-run returns of riskier assets, so holding it for many years trades growth potential for stability. Whether that trade suits a particular person depends on their goals, and general guidance on the trade-off between risk and reward is covered in investment risk and your attitude to risk.

Money market funds are priced and traded once a day

Unlike a share, whose price changes in seconds, most fund prices are set just once a day by the fund manager, usually at noon each working day⁵. Money market funds are traded once daily in the same way¹. Mutual funds are always priced at their net asset value at the close of every trading day, which means the price you deal at reflects the value of everything the fund holds, divided by the number of units⁴.

This has practical consequences for anyone used to instant access. When you place an instruction to buy or sell, it is executed at the next valuation point, not at a live price. There is no minimum period for holding, but you can only buy or sell at that daily valuation point⁵. So a withdrawal request placed in the afternoon is typically priced at the following working day's valuation point, and the proceeds then need to settle to your investment account before they can be moved to your bank. The guide to how funds are priced and when your deal goes through covers this in more detail.

Charges: ongoing, initial and performance fees

Several layers of cost can apply to a money market fund holding, and they are worth separating because they are disclosed in different places.

The first layer is the fund's own charges. The headline figure is the ongoing charges figure (OCF), an annual percentage of your investment paid to the fund manager however the fund performs¹⁰. The OCF takes in the annual management charge plus additional costs such as trustee and auditor fees, taken directly out of the fund¹¹. Funds often also levy an initial fee when you invest, up to 5.5%, and an ongoing charge typically around 1%⁵, though money market funds generally sit well below that typical fund level because they are cheap to run.

The second layer is performance fees. These are not included in the ongoing charge as published by the Association of Investment Companies, which states plainly: "The ongoing charge does not include performance fees." Key Information Documents, by contrast, include transaction costs, gearing costs and performance fees where paid, which are not in the ongoing charge¹². Some sources publish a combined figure, the ongoing charge plus performance fee, which includes the performance fees paid in the last financial year¹³. Reading a single number without knowing which definition it uses can mislead by a wide margin.

The third layer is the platform. Investment platforms may charge each time you buy and sell a share, investment trust or exchange-traded fund, though fees for buying and selling traditional funds are less common¹⁴. Platforms also levy their own ongoing charges for holding investments. The guide to investment platform fees and charges and the page on the ongoing charges figure set out how these work.

For context on scale, fund management charges tend to sit between 0.1% and 0.3% a year for passive funds, with actively managed investments costing more¹⁵. Exit costs are a further category regulators require firms to disclose, including proportional fees and any explicit charges or penalties for early exit¹⁶. Where to find a specific fund's charges is covered in the guide to fund documents: KIDs, KIIDs, factsheets and prospectuses.

Minimum investment

There is no single minimum across the market, because the entry point is set by the fund and the platform together. On some platforms you can normally invest from £100 as a lump sum or £25 per month⁵. More generally, funds can be bought with small amounts, starting from around £50 a month, depending on the fund¹⁷, and the same £50 a month minimum applies to regular saving into investment trusts⁸.

What this means in practice is that a money market fund is not reserved for large investors. Someone wanting to move a few hundred pounds out of cash and into a fund holding can generally do so, though the platform's own minimums and dealing charges apply, and a very small holding can be eaten into by fixed platform fees. The page on the minimum amount you can invest covers how these minimums work across account types.

Money market funds in an ISA or SIPP

Money market funds can be held inside tax wrappers. Many investment platforms offer the ability to hold investments inside an ISA, a SIPP (self-invested personal pension) or a Junior ISA, alongside an ordinary trading account with no special tax benefits, sometimes called a general investment account¹⁸. Holding a money market fund in a wrapper does not change what the fund does; it changes how its returns are taxed, and the page on where investments can be held compares the options.

The ISA rules are in the middle of a significant change. Under regulations made in 2026, money market funds become a qualifying investment for the cash component of an ISA from 6 April 2027⁶. This is not entirely new: regulations in force since 2014 already added short-term money market funds and money market funds as qualifying investments for the cash component²¹. What is new is the tightening around the stocks and shares component.

From 6 April 2027, money market funds are also a qualifying investment for the stocks and shares component, but subject to a condition: 100% of the value of the investments, other than cash, held under that component must not be money market funds⁶. In other words, a stocks and shares ISA cannot be filled entirely with money market funds. The government's factsheet on ISA reform explains the policy aim: "From April 2027 cash-like assets will be defined as Money Market Funds only"²². The draft legislation defines a money market fund by reference to the EU Money Market Funds Regulation, and lists money market funds for both components, with the same 100% condition attached to the stocks and shares component²³.

The scale of cash inside ISAs gives context for why the rules are being tightened. Cash ISAs accounted for 40.5% of the market value of ISA funds at the end of 2022 to 2023, up from 38.4% the previous year²⁵. The reform is aimed at money sitting in ISA wrappers behaving like cash rather than being invested.

Inside a SIPP, the same fund can be held, but pension money is locked away: it is usually not accessible until age 55, rising to 57 from 6 April 2028 unless a protected pension age applies. That makes a money market fund inside a pension a very different proposition from the same fund in an ordinary account, however liquid the fund itself is. The pensions guide covers access rules in full.

Returns are not guaranteed: the risks to understand

The single most important thing to understand about a money market fund is stated by every provider in similar terms: while these funds offer some stability compared with other, riskier investments, returns are not guaranteed⁹. Fidelity's own product page is blunt on two points: "An investment in a money market fund is not guaranteed", and "An investment in a money market fund is different from an investment in deposits, as the principal invested in an money market fund is capable of fluctuation"²⁶. Vanguard says the same: even though it is a low-risk investment, there is still a chance the value of your investments could fall and you might not get back what you invested².

What could actually go wrong? Hargreaves Lansdown identifies the mechanism: "the main risk of money market funds is a default of any of the bond issuers or the issuers of the certificates of deposit it holds"¹. A money market fund lends to governments and large institutions through short-term instruments; if one of those issuers fails to pay, the fund's value drops. The risk is spread across many issuers, which is why it is low, but it is not zero.

Two further points complete the picture. First, these funds can often use derivatives, a type of financial contract valued dependent on underlying assets, which adds risk¹. Second, there is no external backstop: money market funds do not rely on external support for guaranteeing the fund's liquidity or stabilising its value, and the risk of loss of the amount invested is borne by you, the investor². General investment guidance makes the same point at its starkest: in extreme circumstances you could even lose all your money⁸, and no investments are without risk²⁷.

What protection exists is protection against wrongdoing, not against loss. Investors have complaint rights, covered in your rights as an investor, and the Financial Ombudsman Service can look at complaints about ISAs and investments²⁸. But falling value because an issuer defaulted, or because returns were simply lower than expected, is investment risk, not a complaint ground. The pages on what happens if a platform fails, fund suspensions and whether FSCS covers poor performance draw these lines in detail.

Money market fund or savings account: how each one behaves

The comparison people most often want is with a savings account, and the difference comes down to one word: deposit. A savings account, whether at a bank, building society or credit union, is a deposit that pays interest or a share of any profits²⁹. The balance does not fluctuate. A money market fund is not a deposit; its principal is capable of fluctuation and its return is not guaranteed²⁶. Everything else follows from that.

Access is where expectations most often diverge. Even government-backed NS&I products are not instant: withdrawals from Income Bonds and Premium Bonds can take 3 to 5 days to reach your bank account³⁰. A money market fund adds the daily valuation cycle on top of settlement, so the money arrives on a similar sort of timescale in practice, but with less certainty about the exact amount, because the deal is priced at the next valuation point. At the far end of the spectrum, peer-to-peer investments can involve waits of several months to withdraw³², which a money market fund does not.

Which suits a person depends on circumstance rather than on any general rule. A sum needed on a known date in the near future, where the exact amount matters, behaves differently from money that can stay put for years. The pages on investing versus saving and when investing makes sense instead of saving set out that comparison, and the savings accounts guide covers the deposit side in full.

Who offers money market funds and where to get help

Money market funds are bought through investment platforms, the services that hold your investments and let you deal in funds, investment trusts and shares. Platforms allow you to put investments inside tax-efficient wrappers including SIPPs and ISAs, or a general investment account¹⁴, and many offer ISA, SIPP and Junior ISA wrappers alongside an ordinary trading account¹⁸. Several well-known investment businesses publish money market fund ranges and guidance on them, including Hargreaves Lansdown, Quilter, Vanguard, Fidelity and HSBC¹. The guide to how investment platforms work explains what these services do and how they differ.

Before choosing anything, the free and impartial options are worth knowing. MoneyHelper, the government-backed money guidance service, publishes free information on banking and savings products²⁹. Citizens Advice explains how to check whether a financial service has followed the rules³³. If something has already gone wrong with an ISA or an investment, the Financial Ombudsman Service is the free complaints service that can look at it, and its page on ISA complaints explains what it covers²⁸. For the underlying concepts, the investing guide covers funds, risk and platforms from the beginning.