Home Bias: Why Your Portfolio Probably Has Too Much UK

The UK Is About 4% of the World

Start with a fact that surprises most British investors: the UK stock market represents roughly 4% of global equity market capitalisation. The US accounts for around 60%. Japan, France, and China each have larger stock markets than the UK.

If you were building a portfolio from scratch with no preconceptions — simply buying the world's companies in proportion to their size — you'd put about 4p of every pound into UK stocks.

Most UK investors hold significantly more than that. In many cases, much more.

This is home bias. And until very recently, even the UK's most popular passive funds were designed to encourage it.

What Home Bias Actually Is

Home bias is the tendency for investors to disproportionately favour domestic stocks over international ones. It's one of the most well-documented behavioural patterns in finance, observed in virtually every country with a stock market.

American investors overweight US stocks. Japanese investors overweight Japanese stocks. British investors overweight the FTSE.

The reasons are intuitive. You know British companies. You shop at Tesco, fill up at Shell, bank with Barclays. The names on the FTSE 100 are familiar. Foreign companies feel abstract and risky. The FTSE is quoted on every news bulletin. The S&P 500 feels like someone else's market.

There's also a practical comfort: UK stocks are denominated in sterling, so there's no currency risk. When you hold international equities, your returns are affected by exchange rate movements as well as stock performance. If the pound strengthens against the dollar, your US holdings are worth less in sterling terms — even if the underlying shares haven't moved.

These aren't irrational concerns. But they've led to a structural overweight that, for most investors, does more harm than good.

The Cost of Staying Too Close to Home

The UK market is not the global economy in miniature. It has specific characteristics that make it a poor proxy for worldwide growth.

Sector concentration. The FTSE 100 is heavily weighted toward financials, energy, mining, consumer staples, and pharmaceuticals. It has very little exposure to the technology sector that has driven global equity returns for the past 15 years. The UK's largest tech company wouldn't crack the top 50 in the US.

Slower growth. UK equities have materially underperformed global markets over most meaningful time periods. Over the decade to 2025, a global tracker fund returned roughly double what a FTSE All-Share tracker delivered. An investor who overweighted UK stocks wasn't just missing diversification — they were missing returns.

Demographic and economic headwinds. The UK faces specific structural challenges — lower productivity growth, Brexit-related trade friction, an ageing population — that don't apply uniformly to the rest of the world. Overweighting UK equities is, in effect, making a concentrated bet on the UK economy outperforming. History suggests that's not a bet worth doubling down on.

Dividend dependency. UK investors have historically been drawn to FTSE stocks for their dividends. And it's true — the FTSE 100 has a higher dividend yield than most global indices. But dividends aren't free money. They come out of share prices, and a high yield can mask low total returns. A company paying a 5% dividend while its share price goes nowhere is not outperforming a company paying 1% while its price grows by 15%.

Vanguard's LifeStrategy Change

For years, Vanguard's LifeStrategy funds — among the most widely held investment products in the UK — built a deliberate UK overweight into their design. The LifeStrategy 80% Equity fund, for example, held approximately 20-25% in UK equities. That's five to six times the UK's share of the global market.

Vanguard's rationale was reasonable on its face: UK investors have UK-denominated liabilities — mortgages, bills, retirement spending — so holding more UK assets reduces currency mismatch. There was also a nod to the familiarity argument: investors feel more comfortable seeing companies they recognise in their portfolio.

But in 2025, Vanguard announced a significant review of this positioning. They reduced the UK overweight in the LifeStrategy range, bringing UK equity allocation closer — though not all the way — to the UK's actual global market weight. The shift moved UK exposure meaningfully downward, with the difference reallocated to global equities.

This wasn't a dramatic headline event. It was disclosed in fund updates and glide path documentation. But for the millions of UK investors in these funds — many of whom chose LifeStrategy precisely because they didn't want to make asset allocation decisions themselves — it was one of the most consequential portfolio changes in years.

Vanguard's reasoning, as laid out in their research, was straightforward. The benefits of home bias — reduced currency volatility, investor comfort — had been outweighed by the costs: lower diversification, sector concentration, and foregone global returns. The world had changed. The UK market had become a smaller and less representative slice of the global economy. Maintaining a large overweight was no longer justifiable on evidence.

Why This Matters More Than It Sounds

If you're reading this and thinking "it's just a few percentage points," consider the compound effect.

An investor contributing £500 a month for 30 years into a portfolio with a 25% UK weighting versus one with a 10% UK weighting could see a material difference in outcomes — not because the UK market will definitely underperform, but because the more diversified portfolio captures a broader set of global growth opportunities and reduces concentration risk.

Over three decades, a few percentage points of annualised return compound into tens of thousands of pounds. The difference between retiring comfortably and retiring anxiously can come down to decisions that felt minor at the time.

This is also why it matters that Vanguard made the change. LifeStrategy funds are default choices — the products people select when they don't want to build a portfolio from scratch. Defaults shape outcomes for millions. When the default carries a significant home bias, millions of investors end up overweight UK equities without ever actively choosing to be.

The Currency Risk Question

The strongest argument for home bias is currency risk. If you're spending pounds in retirement, holding assets in pounds reduces the volatility of your real returns.

This is true — but less meaningful than it appears over long time horizons.

Over short periods, currency fluctuations can significantly affect the sterling value of international holdings. If the pound rises 10% against the dollar in a year, your US equity returns take a corresponding hit in sterling terms.

But over 20 or 30 years, currency effects tend to wash out. Currencies move in both directions, and the long-term trend reflects fundamentals — productivity, inflation, interest rates — rather than short-term swings. The investor who avoided global equities for 30 years to dodge currency risk almost certainly sacrificed far more in foregone returns than they saved in volatility reduction.

There's also a natural hedge that's often overlooked: many companies in a global index — Nestlé, Toyota, Microsoft — earn revenues in dozens of currencies. Owning a globally diversified company isn't the same as holding a single foreign currency.

What a Sensible UK Allocation Looks Like

There's no single right answer, but the evidence points in a clear direction.

A pure market-cap weighting would put roughly 4% in the UK. That might feel uncomfortably low to British investors, and there are reasonable arguments for a modest tilt above that — sterling-denominated spending, slightly lower volatility, and some diversification benefit from the FTSE's unique sector composition.

Something in the range of 5-15% UK equity exposure is where most evidence-based portfolio constructors land. Below the UK's weight and you're actively underweighting. Above 20% and you're making a concentrated bet on the UK economy that you probably haven't modelled.

The important thing is to make it a conscious choice. If your portfolio holds 25% UK equities, you should know why — and "because I didn't think about it" isn't a good enough reason when it affects your retirement.

Check Your Own Portfolio

Most investors don't actually know their UK weighting. They know they hold "a global fund" or "a pension" — but they haven't looked at the geographic breakdown.

Here's what to check:

1. Log into your pension or ISA provider. Look at the fund factsheet for whatever you're invested in. There will be a geographic or regional breakdown — find the UK percentage.
2. Add up across accounts. If you hold multiple funds across a workplace pension, a SIPP, and an ISA, you need to look at the aggregate UK weighting, not each fund in isolation.
3. Include individual stocks. If you hold individual UK shares alongside your funds, that's additional UK exposure on top of whatever the funds already hold.
4. Compare to global weight. If your total UK equity exposure is above 15-20%, ask yourself whether that's a deliberate, informed choice — or just the default you ended up with.

The Bigger Lesson

Home bias is just one example of a broader problem in investing: the things that feel comfortable are often the things that cost you money. Holding UK stocks feels safe because they're familiar. But familiarity isn't the same as diversification, and comfort isn't the same as optimality.

Vanguard's decision to reduce their UK overweight isn't radical. It's an overdue acknowledgement that the world's largest low-cost fund provider was building a behavioural bias into its products — and that the evidence no longer supported it.

If Vanguard has looked at the data and moved, it might be worth looking at your own portfolio and asking: am I overweight UK because I chose to be, or because nobody told me I had a choice?

Further Reading

• Vanguard. "Vanguard LifeStrategy funds: Glide path and asset allocation review." 2025.
• Coval, J. & Moskowitz, T. (1999). "Home Bias at Home: Local Equity Preference in Domestic Portfolios." Journal of Finance, 54(6), 2045–2073.
• French, K. & Poterba, J. (1991). "Investor Diversification and International Equity Markets." American Economic Review, 81(2), 222–226.
• Dimson, E., Marsh, P. & Staunton, M. (2025). Credit Suisse Global Investment Returns Yearbook. On long-term country-level equity performance.
• Pension Craft (Ramin Nakisa). "UK Home Bias — How Much UK Should You Hold?" YouTube.