International Diversification: The Case Against Home Bias
Investors everywhere hold far more of their own country's shares than its size in global markets would suggest. The arguments on both sides of that habit deserve a fair hearing.
What home bias is, and how common it is
Home bias is the tendency to hold a much larger share of your own country's shares than that country represents in global equity markets. It shows up almost everywhere it has been measured. Studies of investor portfolios in the United States, the United Kingdom, Canada, Australia and Japan have consistently found domestic allocations far above each market's global weight, often by a factor of two or more. Some of this has sensible roots — familiarity, tax treatment of domestic dividends, pension rules, matching assets to future spending in your own currency — and some is simply the path of least resistance in whatever default options a retirement plan offers. For scale, the United States made up roughly 60% to 65% of a broad global equity index by market value as of mid-2026, meaning a market-weighted global allocation looks heavily American to an investor elsewhere, and surprisingly international to an American.
The case for looking beyond your own market
The core argument is not that foreign companies are better. It is that different markets are exposed to different things. National indexes have genuinely different sector compositions — some are dominated by technology, others by banks, commodity producers, industrials or consumer staples — so holding several of them spreads exposure across different economic engines. Valuations also diverge for long periods, and a market's starting valuation has historically had some relationship with its subsequent long-run returns, though a loose one. Currency adds a third layer: when your own currency weakens, foreign holdings are worth more in it, which can cushion a portfolio precisely when domestic conditions are deteriorating. And leadership rotates. After more than a decade in which US equities outpaced most of the rest of the world, developed international markets outperformed the US by a wide margin in 2025 — a reminder that these cycles are long enough to feel permanent from inside them.
- Sector mix: national markets are shaped by their economies, so combining them dilutes exposure to any single industry's fortunes.
- Valuation dispersion: markets rarely trade at the same multiples at once, and those gaps can persist for years.
- Currency: holding assets in several currencies reduces dependence on one, at the cost of added short-term volatility.
- Rotation: the best-performing region of one decade has frequently not led the next, and predicting the handover has proved difficult.
Every argument for concentrating in your home market has at some point been made most confidently in the country that was about to spend a decade lagging.
The counter-arguments, taken seriously
The most substantial objection is that large domestic companies already provide global exposure. A multinational listed in one country may earn most of its revenue in dozens of others, so an investor holding a domestic large-cap index already owns a claim on worldwide economic activity. The response is that revenue geography and share price behaviour are not the same thing — domestic listings tend to move with domestic sentiment, interest rates and policy regardless of where the sales are booked — but the objection is not empty. Currency is the second: it diversifies, but it also adds volatility unrelated to the underlying businesses, and hedging it costs money. Third, there is the plain historical record that international diversification detracted from returns for US investors through much of the 2010s and into the 2020s, and detracted for investors in other markets during their own domestic booms. Diversification is not free; the price of not having all your money in the best market is not having all your money in the best market.
The debate has become livelier recently for a specific reason: global market-weighted indexes have grown unusually concentrated. As of the second half of 2026, the ten largest holdings of a broad global equity index accounted for roughly a quarter of its value, most of them a handful of very large American technology companies. That cuts in two directions at once. To some it strengthens the case for deliberately holding more outside the United States, on the grounds that a market-weighted global fund is now a concentrated bet in disguise. To others it simply reflects the global scale and profitability of those businesses, and diversifying away from them has been an expensive habit. Both readings are defensible, and neither is settled by the evidence available today. Nothing here is a view on whether any region will outperform. Index weights and market conditions change continually, so verify current figures from primary sources.
This article is educational and general in nature. It isn’t personalized investment, tax, or legal advice — always weigh your own circumstances, or talk to a licensed professional, before making financial decisions.