Home Bias in Investing: Why Domestic Overweighting Costs Investors and How to Correct It

One of the most persistent and well-documented anomalies in investment behaviour is home bias: the tendency of investors in every country to allocate disproportionately to domestic equities relative to what a globally diversified portfolio would suggest. UK investors are not uniquely prone to this bias — it appears in virtually every country where the data has been examined — but the gap between domestic allocation and rational diversification is large enough to have a meaningful long-term impact on returns.

The Scale of the Problem

The UK represents approximately 3.5–4% of global equity market capitalisation as measured by indices such as the MSCI All Country World Index (ACWI) or the FTSE All-World. A purely market-weighted global portfolio would therefore hold around 4% in UK equities, with the remainder distributed internationally — predominantly the US (around 65% of MSCI ACWI), Europe, Japan, and emerging markets.

Survey data and analysis of household financial assets consistently shows that UK investors hold somewhere between 25–40% of their equity portfolios in UK stocks. The investment platform and fund selection data broadly confirms this: UK equity funds, UK income funds, and FTSE 100 trackers remain disproportionately popular relative to global market weight.

The pattern is not unique to the UK. Academic research on the equity home-bias puzzle (including work by Lieven Baele and others) has found that French investors allocate a substantial majority of their equity holdings to French stocks; German investors hold a similarly outsized share of German equities; Japanese investors have historically maintained large domestic allocations. In each case, the domestic market's share of global capitalisation is a fraction of the home allocation.

Why Home Bias Exists

Several rational and irrational factors contribute to home bias:

Familiarity. Investors are more comfortable with companies they know — whose products they use, whose headquarters they can name, whose quarterly results appear in the domestic press. Familiarity creates an (often unfounded) sense of superior information. Warren Buffett's "invest in what you know" is frequently cited to justify domestic concentration, misapplying advice intended about the competitive dynamics of individual companies to the entirely different question of geographic diversification.

Currency familiarity. Sterling-based investors feel intuitively that investing in GBP-denominated assets avoids currency risk. This reasoning has some validity for spending that will definitely occur in sterling — but for investors who may retire abroad, maintain international properties, or have children in foreign universities, the currency argument for domestic concentration is weaker than it appears.

Tax treatment. Historical quirks of UK tax policy — dividend tax credits, certain pension fund rules — have at times favoured domestic equities. These advantages have substantially diminished, but the allocation habits they created have persisted.

Benchmark and professional convention. Until relatively recently, many UK professional investors used UK equity indices as their default equity benchmark, leading to domestic overweighting that filtered through to retail products.

Irrational familiarity bias. Beyond rational explanations, there is a purely psychological component: domestic assets simply feel safer, more legible, and less uncertain. This is a cognitive bias, not a financial argument.

The Cost of Home Bias: UK vs Global Equities

The long-run return comparison between UK equities and globally diversified equity portfolios is instructive, though past performance is not a reliable guide to future results.

Over the 20 years to 2025, the MSCI World Index (developed markets, GDP-weighted approximately 65% US) delivered significantly higher total returns than the FTSE All-Share. The difference in annualised returns has varied across studies and time periods, but figures in the range of 2–4 percentage points per year have been documented in comparisons across the decade to 2025 — with much of the gap attributable to the strong performance of US technology companies, particularly the mega-cap growth stocks that dominate MSCI World.

A 3% annualised return differential, sustained over 20 years, is compounding at scale. £500,000 growing at 8% annually reaches approximately £2.3 million; at 5% annually, it reaches approximately £1.3 million. The cost of concentrated domestic exposure — relative to a market-weighted global portfolio — is not a rounding error.

It is important to note that the comparison is context-dependent. The UK outperformed global equities during certain periods, notably in the early 2000s when UK value stocks held up better than the tech-heavy MSCI World. The argument for global diversification is not that the UK will always underperform but that concentration in any single market increases risk without a commensurate expected return premium.

How Much UK Exposure Is Reasonable?

A small, genuinely informed tilt towards UK equities can be justified for certain investors:

Sterling spending requirements. Investors with a high proportion of expected future expenditure in sterling and no meaningful foreign currency exposure elsewhere in their balance sheet have a legitimate reason to hold somewhat more UK equities as a partial currency hedge.

UK-specific tax advantages. ISA and SIPP investments grow free of UK tax, but the vehicle's tax treatment does not depend on the geographic allocation within the vehicle. UK dividend tax credits no longer provide a structural advantage.

Valuation. At certain points in the cycle, UK equities have traded at significant valuation discounts to global peers — as they did in the aftermath of the Brexit vote and persistently through the early 2020s. A conscious valuation-based tilt is different from unconsidered home bias.

For most internationally mobile HNW investors, a UK equity allocation of 10–15% of the total equity portfolio — roughly two to four times the UK's global market weight — represents a generous allowance for these factors. Allocations of 30–40% are difficult to justify on any principled basis for investors who do not have overwhelming sterling spending requirements.

Practical Correction: Tools for Global Diversification

The most straightforward route from a UK-heavy portfolio to global diversification is through index funds and ETFs that provide broad market-weight exposure:

MSCI World ETFs (e.g., iShares Core MSCI World UCITS ETF, Vanguard FTSE Developed World UCITS ETF) provide exposure to large and mid-cap developed market equities across 23 countries, with ongoing charges in the range of 0.12–0.22% annually.

MSCI ACWI ETFs extend the developed-world exposure to include emerging markets, providing a more complete global allocation.

FTSE All-World ETFs (e.g., Vanguard FTSE All-World UCITS ETF) cover approximately 4,000 stocks across 49 countries, with an ongoing charge of around 0.22%.

Within a UK ISA or SIPP, any of these vehicles provide global equity diversification with the full benefit of the UK tax wrapper, making the notion that a UK wrapper requires UK investment holdings an error of framing.

For investors with taxable portfolios — including offshore investment bonds and directly held portfolios — the same diversification principle applies, with additional consideration for whether hedged or unhedged currency exposure is appropriate.

Home Bias in Multi-Asset Portfolios

Home bias also appears in fixed income allocation. UK investors tend to hold predominantly sterling-denominated bonds, which is more defensible for fixed income than for equities — currency movements have a much larger proportional impact on bond returns relative to equity returns, and sterling bond exposure naturally matches sterling liabilities.

However, for investors with international balance sheets — properties in multiple jurisdictions, income from multiple currencies, anticipated foreign spending — a more genuinely multi-currency fixed income approach may be appropriate.

Compliance and Regulatory Note

Investments in overseas markets are subject to currency risk as well as market risk, and returns may increase or decrease as a result of movements in exchange rates. The past performance of specific markets or indices is not a reliable indicator of future results. Investments can fall as well as rise in value and investors may not recover the full amount invested. Tax treatment depends on individual circumstances and may change. This article is for information only and does not constitute personal financial advice.

How Global Investments Can Help

For internationally mobile high-net-worth individuals, home bias is often especially counterproductive. Clients who maintain properties across multiple jurisdictions, hold assets in several currencies, and anticipate spending across multiple countries have balance sheets that are already inherently global — their investment portfolios should reflect this reality. At Global Investments, we construct portfolios from first principles, examining each client's full balance sheet, currency exposures, and future liabilities before determining geographic allocation. We do not default to domestic equity overweighting. If you would like to review the geographic composition of your portfolio and assess whether home bias is a structural drag on your long-term returns, please contact our advisory team.