S&P 500 vs Global Index Fund: Should UK FIRE Investors Chase US Returns?
The S&P 500 has left the rest of the world behind for more than a decade, and every few months r/FIREUK asks the same question: why not just put everything in the US? Here’s the honest case for each option, what a global fund already holds, and the currency and tax details that matter for UK investors.
Published: 9 October 2026 at 07:08 · 8 min read
S&P 500 or Global Index Fund: Which Is Better for UK FIRE?
For most UK FIRE investors, a global index fund is the more robust default — it already holds around 60–65% US shares, so you get most of the US upside without betting your whole retirement on one country. The S&P 500 has delivered higher returns recently, but a FIRE portfolio may need to last 40 or 50 years, and no single market has led for that long without a lost decade somewhere along the way.
The two options side by side (approximate figures):
| S&P 500 tracker | Global all-world tracker | |
|---|---|---|
| Holdings | ~500 large US companies | ~4,000 companies in 40+ countries |
| US weighting | 100% | ~60–65% |
| Top 10 holdings | ~35–40% of the fund | ~25% of the fund |
| Typical OCF | ~0.03–0.10% | ~0.12–0.23% |
| Dividend yield | ~1.3% | ~1.8% |
| Annualised GBP return, 10 yrs to end 2024 | ~15% | ~11.5% |
| Annualised GBP return, 2000–2009 | ~−1% | ~0% |
| Currency exposure | US dollar only | Mostly dollar, plus euro, yen, sterling and others |
Notice the framing: you’re not choosing between “US” and “not US”. You’re choosing whether the last 35–40% of your equities goes into Europe, Japan, the UK and emerging markets, or into more of the same US companies you already own.
Why Has the S&P 500 Beaten the World?
Three things drove most of it: faster US earnings growth (especially from a handful of technology giants), rising valuations, and a weaker pound. Only the first is something you can reasonably expect to continue, and even that isn’t guaranteed.
- Earnings. Companies such as Apple, Microsoft, Nvidia, Amazon and Alphabet grew profits far faster than the average listed company elsewhere.
- Valuations. Investors became willing to pay more for each pound of US earnings. The S&P 500’s cyclically adjusted price-to-earnings ratio has been in the mid-30s, roughly double its long-run average and well above most other markets. Higher starting valuations have historically been followed by lower long-term returns.
- Currency. The pound fell from around $1.56 at the end of 2014 to about $1.25 at the end of 2024, adding roughly 2 percentage points a year to sterling returns from any dollar asset. That tailwind can turn into a headwind.
It’s also worth remembering how leadership has shifted before. In 1989 Japan made up around 40% of the world stock market, more than the US at the time. Japan’s main index then took 34 years to get back to its 1989 peak. Nobody can say whether the US is closer to 1989 Japan or simply to another decade of dominance — which is exactly the argument for not having to know. For long-run figures across markets, see our guide to historical index fund returns in the UK.
What Does Concentration Risk Mean for a FIRE Portfolio?
Concentration risk matters more for FIRE than for a typical saver because you’ll be selling to fund your spending for decades, so a long flat period early in retirement can do lasting damage. This is sequence-of-returns risk, and it bites hardest when your whole portfolio depends on one market.
To see why the return assumption matters so much, here’s what a £300,000 pot could grow to over 20 years at different real (after-inflation) returns:
| Real return a year | Pot after 20 years | Income at 4% |
|---|---|---|
| 3% | £541,800 | £21,700 |
| 5% | £796,000 | £31,800 |
| 7% | £1,160,900 | £46,400 |
An all-US portfolio widens the range of outcomes in both directions: it’s more likely to land at the top row if the US keeps winning, and more likely to land at the bottom if it has a lost decade. A global fund narrows that range. For a plan that has to work rather than one that has to win, a narrower range is usually worth more. This is also why sensible FIRE plans assume a modest withdrawal rate rather than projecting the last decade forward.
What About Holding Both?
Holding a global fund plus an S&P 500 fund is a deliberate US overweight, not extra diversification — fine if that’s your intention, but worth doing knowingly. Here’s how common splits change your overall US exposure:
| Portfolio | Approx. US exposure | Non-US exposure |
|---|---|---|
| 100% global all-world | ~63% | ~37% |
| 70% global / 30% S&P 500 | ~74% | ~26% |
| 50% global / 50% S&P 500 | ~81% | ~19% |
| 100% S&P 500 | 100% | 0% |
The danger isn’t the split itself; it’s drift driven by recent performance. Investors who add more US after every strong year end up most concentrated just when valuations are highest. If you choose a split, write it down and rebalance back to it once a year. And if you want more home-country exposure rather than less, read global vs UK index funds for FIRE.
What Currency and Tax Points Matter for UK Investors?
Hold either fund in a Stocks & Shares ISA or SIPP, use a UK-available UCITS version, and accept that an S&P 500 fund is a pure dollar bet in sterling terms. The practical details:
- You can’t usually buy VOO or SPY. US-listed ETFs lack the UK key information document retail investors need, so UK platforms offer Irish-domiciled UCITS ETFs (such as VUAG or CSP1) and UK index funds instead.
- US withholding tax. Irish-domiciled funds typically lose 15% of US dividends to US withholding tax at fund level. On a yield of around 1.3%, that’s a drag of roughly 0.2% a year — it applies to the US slice of a global fund too, and you can’t reclaim it inside an ISA.
- Currency. Most S&P 500 and global trackers are unhedged. Your future spending is in pounds, so a large single-currency position adds risk. Sterling-hedged share classes exist but cost a little more and remove the currency cushion in a crash.
- Wrappers. Inside an ISA (£20,000 a year) or SIPP, dividends and gains are tax-free. In a general investment account, dividends above £500 and gains above £3,000 a year are taxable — see gov.uk on Capital Gains Tax.
Don’t forget the UK income you’ll get anyway. The full new State Pension of £11,502 a year (2025/26) from 67 is a sterling, inflation-linked income stream — check your forecast on gov.uk. For help picking a specific fund, see the best global index funds in the UK.
Frequently Asked Questions
Is the S&P 500 better than a global index fund for UK investors?
Over the last decade, yes: the S&P 500 returned roughly 15% a year in sterling to the end of 2024, against around 11.5% for a global all-world tracker. Over longer and different periods the picture changes. From 2000 to 2009 the S&P 500 returned slightly less than nothing a year in sterling. A global fund already holds around 60 to 65% US shares, so the real choice is whether to put the remaining 35 to 40% into the US as well. Most UK FIRE investors stick with global for diversification rather than betting that the past decade repeats.
How much of a global index fund is in the US?
Around 60 to 65% of a typical FTSE All-World or MSCI ACWI tracker is invested in US companies, and the S&P 500 alone makes up roughly half of the world stock market by value. The UK is only about 3 to 4%. So a global tracker already gives you heavy US exposure, including all the large US technology companies, while keeping a third or more in Europe, Japan, the UK and emerging markets.
Can I buy an S&P 500 fund in a Stocks & Shares ISA?
Yes. UK platforms offer S&P 500 index funds and UK-listed ETFs, with ongoing charges from around 0.03% to 0.10%. Examples include Vanguard S&P 500 UCITS ETF (VUAG or VUSA), iShares Core S&P 500 (CSP1) and index funds from HSBC, Fidelity and L&G. Retail investors in the UK generally cannot buy US-listed ETFs such as VOO because they lack the required UK key information document, so UK investors use Irish-domiciled UCITS versions instead.
Does currency risk matter when investing in the S&P 500 from the UK?
Yes. An unhedged S&P 500 fund is effectively a dollar asset, so your sterling return depends on both US share prices and the pound-dollar exchange rate. The pound fell from around $1.56 at the end of 2014 to about $1.25 at the end of 2024, which added roughly 2 percentage points a year to sterling returns. If the pound strengthens, the reverse happens. A global fund is also mostly unhedged but spreads currency exposure across the dollar, euro, yen and others.
Is it a good idea to hold both a global fund and an S&P 500 fund?
It is a common middle ground, but be clear about what it does. Holding 70% global and 30% S&P 500 lifts your US exposure from around 63% to roughly 74%, and 50/50 takes it to about 81%. That is a deliberate overweight to the US, not extra diversification. If you do it, decide the split once, write it down and rebalance to it, rather than adding more S&P 500 every time it has a good year.
Work Out Your Own Numbers
Whichever fund you choose, your plan should rest on a cautious return assumption, not the best decade on record. Use our free calculators to stress-test it:
- FIRE Number Calculator — work out how big your portfolio needs to be for your target spending, including the State Pension
- Safe Withdrawal Rate Calculator — see how different withdrawal rates and return assumptions affect how long your money lasts
For a wider look at fund options, read our guide to the best index funds for FIRE in the UK.
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