The boring basket, explained properly
Nine out of ten. That is roughly how many actively managed UK equity funds failed to beat their benchmark last year, according to S&P Dow Jones Indices. An index fund does not try to beat the benchmark. It simply is the benchmark, and in 2025 that was enough to finish ahead of the large majority of professionals trying to outsmart it.
This guide explains what index funds are, how to choose one and how to invest in them from the UK. Nothing here is a recommendation to buy anything. This only explains how they work so you can make your own decision.
What an Index Fund Actually Is
An index is a list. The FTSE 100 is a list of the hundred largest companies on the London Stock Exchange. The S&P 500 is a list of five hundred large American companies. A global index, such as the FTSE All World or the MSCI ACWI, is a collection of thousands of companies across dozens of countries.
An index fund buys everything on that list, in proportion to each company’s size, and then holds it. When a company grows, it takes up a larger amount of the fund. When a company shrinks or drops off the list, the fund adjusts automatically. Nobody is picking favourites, and nobody is trying to guess which company does well next year. That is the entire idea, and it is also why the fees can be so low.
I made the case for this approach in more personal terms in The Boring Basket That Beat My Best Idea. This guide is the practical companion to that piece.
Why So Many People Choose Them
The first reason is cost. The cheapest global tracker funds available to UK investors charge between roughly 0.07 and 0.23 per cent a year, according to comparison site Monevator’s data from March 2026. Actively managed funds commonly charge several times that, and every fraction of a percentage point comes out of your return, every year, compounding against you.
The second reason is performance. S&P Dow Jones Indices publishes a regular scorecard comparing active funds with their benchmarks, and its 2025 results for UK equity funds were stark. Around 88 per cent of broad UK equity funds and 97 per cent of UK smaller company funds underperformed their benchmark over the year. Some active managers do beat the market, but identifying them in advance is difficult, and past winners have a stubborn habit of not repeating.
The third reason is simplicity. You do not need an opinion on any individual company. You need an opinion on whether the market as a whole is likely to grow over the long term, which is a far easier question to live with.
Choosing Which Index
This is the real decision, and it deserves more thought than the provider.
A country index, such as the FTSE 100, ties your fortunes to one economy and, in the FTSE’s case, to a handful of large sectors such as energy, banking and mining. The S&P 500 tracks America’s largest companies; currently it’s dominated by a small group of technology giants. A global index spreads your money across developed and emerging markets in proportion to their size, which currently means six tenths in the United States, with the rest of the world included.
For many beginners, a global fund is the simplest starting point because it removes the need to decide which country will do best. That is not a recommendation, simply the logic most people use when they choose one.
Fund or ETF
Index funds come in two main wrappers. A traditional index fund, sometimes called a tracker or OEIC, is bought and sold once a day at a single price. An exchange-traded fund, or ETF, trades on the stock exchange throughout the day like a share.
For someone investing a regular monthly amount and leaving it alone, the difference is small. Some platforms charge less to hold ETFs and some charge less to hold funds, so the right choice often depends on where you invest rather than the product itself.
Accumulation or Income
Most index funds come in two versions. Income units pay out dividends to you as cash. Accumulation units automatically reinvest them back into the fund. If you are building wealth over the long term and don’t need income now, accumulation units reinvest for you, removing one more decision you might otherwise forget.
How to Actually Invest
The process in the UK is simple. First, choose an investment platform and compare its fees, since the platform charge is added on top of the fund’s own charge. Second, open a stocks and shares ISA on that platform, which shelters your investments from UK tax on gains and dividends. The ISA allowance for the 2026/27 tax year is £20,000. Third, search for the index fund you have chosen, decide on an amount and confirm the purchase. Many platforms let you set up a regular monthly investment, which removes the temptation to time the market.
Then comes the hardest step: leaving it alone.
What Can Go Wrong
An index fund owns the market, so when the market falls, it falls too, sometimes by a third or more. It offers no protection against a broad downturn. It simply ensures you are not doing worse than the market because of an unlucky choice of companies. You can get back less than you put in, and money you may need within the next few years is generally better kept out of shares altogether.
The other risk is behavioural. The most common way people lose money with index funds is by selling during a fall and missing the recovery. The fund does its job. The investor has to do theirs.
Investing carries risk, and this article is not financial advice. If you are unsure whether investing is right for your circumstances, speak to a regulated financial adviser.
The Short Version
Pick an index you understand. Hold it in a tax-efficient wrapper. Keep the costs low. Invest regularly. Do not interfere. It is the least exciting plan in finance, and that is exactly why it tends to work.
The Jacqueline Brand — knowledge builds confidence, confidence builds wealth. This is editorial commentary for inspiration, not financial or professional advice. Always do your own research. The Collection
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