Index Funds vs ETFs in the UK: Which Is Cheaper and Which Should You Hold?

What Is the Difference Between an Index Fund and an ETF?

In the UK, an “index fund” usually means an OEIC or unit trust tracker bought at one price a day through your platform, while an ETF is a tracker listed on a stock exchange and traded like a share during market hours. Both pool investors’ money to track an index such as the FTSE All-World or the S&P 500, both are low cost, and both can be held in a Stocks & Shares ISA, SIPP, Lifetime ISA or general investment account (GIA). The mechanics differ:

Many fund houses offer the same index in both formats. HSBC FTSE All-World Index is an OEIC; Vanguard’s FTSE All-World is available as an ETF (VWRP) and Vanguard also runs OEIC trackers. If you’re choosing which index to own in the first place, see the best global index funds in the UK.

Which Is Cheaper: Index Funds or ETFs?

On small pots an OEIC on a percentage-fee platform is often cheapest; above roughly £25,000–£30,000, an ETF on a capped or free platform usually wins. The fund charge barely moves the needle — the platform’s charging model does. The table shows illustrative yearly costs for a global tracker in four common set-ups:

On the same percentage-fee platform, the ETF costs more at £10,000 because the £18 a year of dealing charges outweighs the platform fee saved. The break-even sits at about £27,000: above that, the capped fee makes the ETF steadily cheaper, and at £250,000 it saves over £500 a year. A flat-fee platform narrows the gap for OEICs, and a free app is cheapest at every size — though apps usually offer ETFs only, with fewer account types and less established customer service. Our UK investing platform comparison explains each charging model in more detail.

How Much Does the Choice Cost Over a FIRE Timeline?

Investing £500 a month for 30 years, holding an ETF on a capped platform leaves you about £17,700 better off than holding an OEIC on a 0.25% uncapped platform — and £37,200 better off than a 0.45% platform. The figures assume a 7% annual return before fees, with fees deducted every year. Total paid in is £180,000 in each case.

The lesson isn’t “ETFs good, OEICs bad” — an OEIC on a flat-fee platform beats an ETF on a capped one. It’s that an uncapped percentage fee on a growing pot is the expensive combination. The gap widens in retirement: on a £600,000 drawdown pot, a 0.25% uncapped platform fee is £1,500 a year, against £45 for a capped ETF. That’s nearly £1,500 of extra spending money every year at a 4% withdrawal rate. For more on fund charges themselves, see the cheapest index funds in the UK.

Are Index Funds and ETFs Taxed Differently in the UK?

Inside an ISA or SIPP there is no difference at all: both are free of UK income tax and capital gains tax. That’s where most FIRE investors hold the bulk of their money, using the £20,000 ISA allowance and pension tax relief first. A few points still apply:

• Stamp duty — you pay no 0.5% stamp duty reserve tax when buying ETFs on the London Stock Exchange or units in an OEIC. It only applies to individual UK shares and most investment trusts.
• US dividend withholding — Irish-domiciled ETFs and UK OEICs both typically suffer 15% withholding tax on US dividends inside the fund. It’s already reflected in the fund’s returns and can’t be reclaimed in an ISA or SIPP.
• Reporting fund status (GIA only) — offshore ETFs need HMRC reporting fund status for gains to be taxed as capital gains rather than income at up to 45%. Mainstream UK-facing ETFs have it, but check HMRC’s list of reporting funds before buying in a GIA.
• Excess reportable income (GIA only) — accumulating ETFs report income each year that you must declare as dividends even though nothing is paid out, and add to your base cost for CGT. Accumulating OEICs work similarly through notional distributions. Above the £500 dividend allowance, both are taxable; see our guide to dividend tax for FIRE.

If you’ve filled your ISA and are investing in a GIA, the paperwork is broadly similar for both, but the £3,000 capital gains tax allowance and £500 dividend allowance are small, so the wrapper decision matters far more than the fund format. Current rates are on gov.uk.

Which Should UK FIRE Investors Hold?

Choose the platform first, then hold whichever format that platform charges least for. In practice that gives a simple rule of thumb:

• Pot under about £25,000 on a percentage-fee platform — an OEIC tracker is simplest and usually cheapest: free monthly investing, any amount, no spreads.
• Pot over £25,000–£30,000 on a percentage-fee platform — switch new money (or the whole holding) to the ETF version of the same index if the platform caps ETF fees, or move to a flat-fee platform and keep your OEIC.
• App-based or ETF-only platform — ETFs, with free automated monthly purchases and fractional shares so nothing sits in cash.
• Large SIPP in drawdown — check how the platform charges for drawdown; capped ETF fees or a flat-fee SIPP can save four figures a year.

Two behavioural points matter as much as cost. ETFs trade live, which makes it easy to tinker or panic-sell on a bad day; if you know that’s a risk, the once-a-day OEIC price can be a useful brake. And switching between formats is tax-free inside an ISA or SIPP, but avoid doing it in a GIA without considering capital gains tax. Whichever you pick, set up a monthly direct debit and leave it alone — our step-by-step guide to buying index funds in the UK walks through it. To move to a cheaper platform without losing your tax wrapper, use an ISA transfer rather than withdrawing.

Frequently Asked Questions

Work Out Your Own Numbers

The fund format matters less than which wrapper you hold it in. Use this free calculator to compare your options:

• ISA vs SIPP Calculator — see whether your next pound of tracker investing is better off in a Stocks & Shares ISA or a pension, based on your tax band and planned retirement age

For the bigger picture, read our guides to the Stocks & Shares ISA and SIPPs for FIRE.