ETF vs Index Fund: What Is the Difference? (UK)

The key differences at a glance

An ETF trades on a stock exchange throughout the day at a live price, while an index fund is bought and sold once a day at a single price. Both can track the same index at low cost and both can be held in a stocks and shares ISA or SIPP. The main practical differences come down to how they are traded, priced and bought regularly.

The table below sets out the main points of comparison for UK investors.

Neither structure is inherently cheaper or better. The right choice depends on how often you invest, how much you invest and what your platform charges for each type of trade.

How ETFs work

An ETF is a fund listed on a stock exchange, so its units trade like shares and are priced continuously during market hours. Buyers pay the asking price and sellers receive the bid price, and the gap between the two is the bid-offer spread. ETFs may track an index by holding the underlying assets (physical replication) or by using derivatives (synthetic replication).

Because an ETF is listed, you can buy or sell it whenever the exchange is open, rather than waiting for a once-a-day valuation. That flexibility has a cost: the price you pay includes the spread, and for less liquid ETFs the spread can be wider. Trading outside core market hours can also mean wider spreads, because fewer buyers and sellers are active.

Physical ETFs buy the shares or bonds that make up the index, or a representative sample of them. Synthetic ETFs use swaps or other derivatives to deliver the index return, which can reduce tracking differences but introduces counterparty exposure. Both approaches aim to mirror an index rather than beat it, and both carry the risk that the fund does not track its index exactly.

Most ETFs are structured so that purchases on UK exchanges do not attract the 0.5% stamp duty that applies to UK share purchases. That can be a meaningful difference for larger lump sums, though it should be weighed against dealing charges and spreads.

How index funds work

A UK index fund is usually an OEIC or a unit trust. It is not listed on an exchange; instead it is priced once a day at a valuation point, using forward pricing. Orders placed before the cut-off are dealt at that day's price, and orders placed later are dealt at the next valuation. This structure makes index funds well suited to regular monthly investing.

Forward pricing means you do not know the exact price when you place your order. You submit the instruction, and the fund manager calculates the price at the next valuation point based on the value of the underlying assets. For long-term investors putting money in month after month, that single daily price is rarely a drawback.

Index funds are typically bought through a platform or directly from the fund manager. Many platforms allow regular contributions by direct debit, and some do not charge for buying or selling funds, which can make small monthly amounts cost-effective. The fund itself carries an ongoing charge, and the platform may add its own fee.

Like ETFs, index funds can be held inside a stocks and shares ISA or a SIPP, so the wrapper does not depend on the structure you choose. The decision between the two is mainly about trading style, pricing and cost rather than about what the fund invests in.

Costs: what to compare

Compare four costs: the ongoing charges figure of the fund, the platform fee, any dealing charge per trade, and the bid-offer spread on ETFs. A low headline charge can be outweighed by frequent dealing fees, and a fund with no dealing charge can still carry a higher platform fee. Add up the total cost for your own pattern of investing.

• Ongoing charges figure: the annual cost of running the fund, deducted from the fund's assets. Compare like with like, since an ETF and an index fund tracking the same index may have similar charges.
• Platform fee: what the platform charges to hold the investment, often a percentage of the portfolio value. Some platforms charge differently for funds and for listed securities.
• Dealing charges: a fee per trade, common for ETFs and sometimes for funds. Frequent small trades can make these add up quickly.
• Spreads: the difference between the bid and ask price on an ETF. This is a cost of trading rather than an annual charge, and it varies with liquidity.

For a lump sum held for many years, a low ongoing charge and a narrow spread may matter most. For regular monthly contributions, the absence of dealing charges on funds can be more significant than a small difference in the ongoing charge. Working through the numbers for your own amounts and frequency gives a clearer picture than comparing headline charges alone.

Which suits regular monthly investing

Index funds often suit regular monthly investing because many platforms let you buy them without a dealing charge, so small contributions are not eroded by fees. ETFs can also be bought regularly, but each purchase may count as a separate trade with its own dealing fee, and the cost varies by platform.

If you invest a fixed amount each month, the arithmetic is straightforward. A dealing charge of a few pounds on a small monthly contribution is a large proportion of that contribution. Where a platform offers free regular fund purchases, an index fund can keep more of each payment invested. Where a platform charges low or no dealing fees for ETFs, the gap narrows.

Some platforms offer regular investing into ETFs at reduced or no dealing cost, so it is worth checking the specific terms rather than assuming. The spread still applies to each ETF trade, though for large, liquid ETFs it is usually small.

For larger, less frequent purchases, the picture can reverse. A single dealing charge on a substantial lump sum is a small percentage, and the ability to trade during the day may be useful. The choice is therefore less about the product label and more about matching the structure to how you actually invest.

Tax and wrappers

Both ETFs and index funds can be held in a stocks and shares ISA or a SIPP, where returns are sheltered from UK income tax and capital gains tax. Outside a wrapper, dividends and capital gains can be taxable. The ISA allowance is £20,000 per tax year (2026/27).

Inside an ISA or SIPP, the wrapper does the tax work, so the choice between an ETF and an index fund does not change the tax treatment of the investment. The annual allowance applies across all your ISAs, and contributions above it are not sheltered.

Outside a wrapper, dividends above the dividend allowance are taxable, and capital gains above the annual exempt amount may be subject to capital gains tax. The tax rules and allowances can change, so it is worth checking the current position on GOV.UK before relying on any figure.

Offshore ETFs have an additional consideration: UK reporting fund status. An offshore fund without reporting status can be taxed less favourably, so investors holding offshore ETFs outside a wrapper should check that the fund has reporting status. Funds domiciled in the UK or in jurisdictions with reporting arrangements are generally simpler on this point.

Protection and risk

Both ETFs and index funds put your capital at risk: the value can fall as well as rise, and you may get back less than you invested. The Financial Services Compensation Scheme covers losses caused by the failure of a firm, not losses caused by market falls. Diversification and a suitable time horizon matter more than the structure you choose.

Market risk applies equally to both. An index fund tracking UK shares and an ETF tracking the same index will both fall if that market falls. Neither structure protects against investment losses, and past performance is not a guide to future returns.

The FSCS can step in if an authorised firm fails and cannot meet its obligations, up to the scheme limits. It does not compensate for poor investment performance or for market movements. Synthetic ETFs carry counterparty exposure through their derivative arrangements, which is a structural risk worth understanding before investing.

For most long-term investors, the more important questions are what the fund tracks, how much it costs and whether it fits a diversified plan. The ETF versus index fund decision is a practical one about trading and charges, not a shortcut to lower risk.

Frequently asked questions

Is an ETF better than an index fund?

Neither is better in general. ETFs trade throughout the day at a live price, while index funds are priced once daily. Costs depend on the platform's dealing and account charges.

Can I hold ETFs in a stocks and shares ISA?

Yes. Most UK platforms allow ETFs and index funds inside a stocks and shares ISA, subject to the £20,000 annual allowance.

Do ETFs pay dividends?

Distributing ETFs pay dividends to investors. Accumulating ETFs reinvest them automatically within the fund.

Is there stamp duty on ETFs in the UK?

Most ETFs do not attract the 0.5% stamp duty that applies to buying UK shares. HMRC sets out when stamp duty applies.

Are ETFs protected by the FSCS?

The FSCS can cover up to £85,000 if an authorised UK firm fails. It does not cover falls in the value of an ETF or fund.