The idea in one paragraph
An index fund doesn’t try to beat the market — it simply is the market. It holds every company in an index (such as the FTSE Global All Cap or MSCI World) in proportion to its size, charges a fraction of what a managed fund charges, and delivers whatever the world’s companies deliver. That sounds unambitious. It has also outperformed the vast majority of professional fund managers over every long period on record.
Why it works
Most managers lose to the market they’re trying to beat. After fees, 80–90% of actively managed funds have underperformed a comparable index over 20-year periods (the S&P SPIVA scorecards track this year after year). The few winners rarely repeat, and there is no reliable way to identify them in advance. Buying the whole market guarantees you the market return — which, perversely, puts you near the top of the league table over time.
Fees compound just like returns. A fund charging 1.5% a year has to beat one charging 0.15% by 1.35% a year, every year, forever, just to break even. Over 30 years, that fee gap turns the same gross performance into a pot roughly 30% smaller. Cost is the single most reliable predictor of fund performance — in the wrong direction.
It removes the two most expensive behaviours. Stock-picking and fund-switching are where private investors lose most of their money. An index fund gives you nothing to pick and nothing to switch, which is precisely the point.
What to look for
- Broad and global. A single global tracker (FTSE Global All Cap, FTSE All-World, MSCI ACWI) covers thousands of companies across dozens of countries. That’s the whole equity job done in one fund.
- Cheap. Ongoing charges (OCF) of 0.1–0.25% are normal for global trackers. Treat anything above 0.5% as a red flag needing justification.
- Physically replicating and large. Mainstream trackers from the big providers (Vanguard, iShares/BlackRock, Fidelity, HSBC, L&G) tick this box.
- The right wrapper. The same fund is available inside an ISA, a pension, or an unwrapped account — hold it inside a wrapper first (see the ISA guide) so returns are never taxed.
Watch platform fees too: the fund’s OCF is only half the cost. A percentage-fee platform can cost more than the fund itself as your pot grows; flat-fee platforms usually win for larger amounts — the fees guide has the full arithmetic.
What index investing does not do
It will not protect you from market falls — you own the market, so you fully experience its crashes. The strategy’s promise is not smoothness; it is that you keep essentially all of whatever the market returns, rather than surrendering a large slice to fees and mistimed decisions. Falls are survived by holding (and ideally continuing to buy), not by predicting.
Getting started, practically
- Open a Stocks & Shares ISA (or use your workplace pension’s fund choices).
- Choose one broad global tracker fund.
- Set up an automatic monthly payment into it.
- Stop. The strategy’s hardest part is that there is no step 5 — no monitoring, no tinkering, no reacting to headlines. Check in once a year.
The uncomfortable truth of investing: activity is a cost, not a virtue. The person who buys a global tracker and forgets the password tends to beat the person who watches the market every day.
Related guides & tools
- Investment fees — the quiet compounding killer — why the 0.1% vs 1.5% choice matters more than fund selection
- Building a diversified portfolio — how one global tracker fits into the bigger picture
- ISA investing — the UK’s best tax shelter — the wrapper to hold it in
- Lump sum or drip-feed — getting money in, and staying invested through crashes
- Financial Planner — model what consistent low-cost investing does to your own numbers
- Investment Fee Impact Calculator — see the pounds difference the 0.1%-vs-1.5% choice makes over decades
Last reviewed: July 2026.