Home bias is the tendency to invest a disproportionate share of one's wealth in the financial instruments of one's own country. Like every bias, it is dangerous, and in investing it does its damage quietly: many investors end up with a large part of their portfolio riding on their home economy without ever having decided to. This article explains where the bias comes from, what the research says about its size, what it costs, and how to keep it in check.
What Home Bias Is and Where It Comes From
An investor in Toronto who fills their portfolio with Canadian banks and Canadian government bonds, a saver in Milan who holds Italian equities and Italian sovereign debt, and an American whose stock exposure is almost entirely the S&P 500 are all showing the same pattern, even though each of them could diversify into foreign markets with a few clicks. The phenomenon is behavioral, and to understand it one has to look at its causes.
The first is familiarity. Domestic companies, banks and brands are better known and therefore feel easier to evaluate. It is natural to feel more comfortable buying shares in a company whose products one uses or whose name appears in the news every day. Knowing a company, however, is not the same as knowing what its stock is worth. The pull of the familiar belongs to the same family as the other cognitive biases that distort trading decisions, and it is just as hard to notice from the inside.
The second is the perception of risk. Investing abroad looks more complex: foreign currencies come into play, along with less familiar companies, different political systems and markets one has never followed. The unknown feels riskier than it is, and the familiar feels safer than it is.
The third is the structure of personal wealth itself. Someone who owns a home in their own country, works for a domestic employer and earns a salary in the local currency already has most of their financial life tied to the national economy before buying a single security. Adding domestic stocks and bonds on top of that does not feel like concentration, because nobody thinks of a job or a home as a position.
How Large the Bias Is
The classic measurement came from Kenneth French and James Poterba in 1991. Using data from the end of 1989, they found that Japanese investors held more than 98 percent of their equity portfolios in domestic stocks, American investors 94 percent and British investors 82 percent, proportions far above what any of those markets represented in the world. That pattern implied something else: investors in each country would have to expect their own market to beat foreign markets by several hundred basis points, an expectation that cannot be true for everyone at once.
Decades of cheap global funds later, the gap has narrowed but not closed. The United States makes up about 60 to 65 percent of the MSCI All Country World Index, a standard yardstick for the global equity market. Yet in the portfolios that financial advisors submitted to Vanguard for analysis, the median allocation to U.S. stocks within the equity portion was 76.9 percent in 2025, down only marginally from 77.9 percent in 2024. Even in the country that is by far the largest slice of the world market, investors overweight home. In smaller markets the gap is wider still, because the home country is a small share of the world and yet takes up a large share of the portfolio.
Why Home Bias Can Cost You
The first cost of home bias flows from one almost automatic consequence: less diversification. Anyone caught by the bias diversifies too little and too narrowly. Diversifying means investing across different markets in order to spread risk among economies, sectors, currencies and growth models. Concentrating on one country creates a dependence on its economic, political and financial conditions. A domestic slowdown, a banking crisis, a rise in the risk premium on government debt or a bout of political instability is then enough to damage the whole portfolio at once. The two diversification methods used in forex rest on the same principle: exposures that do not move together.
The second cost is sector concentration. Stock markets do not all have the same composition. Some countries are heavy in technology, others in commodities, finance, industry or consumer goods. An investor who buys almost exclusively at home also overweights whatever sectors dominate the home index and gives up part of the opportunity set available globally. Canada's index is dominated by banks, miners and energy companies; Australia's by banks and miners; Italy's by banks, utilities and energy; the United Kingdom's by banks, pharmaceuticals, energy and mining; and the American index is unusually heavy in technology. None of these mixes is the world's mix, and a single-country investor inherits the tilt without choosing it.
Then there is sovereign risk. An investor who holds a large amount of domestic government bonds together with shares in domestic banks is more exposed to the country than the portfolio suggests, because banks often hold significant amounts of their own government's debt. Economists call this the sovereign-bank nexus, or the "doom loop," and it was one of the mechanisms that made the euro area's debt crisis so hard to contain: when a government's bonds lose value, the banks that hold them weaken, and a weaker banking system in turn weighs on the government's finances. In periods of stress on the home market, several parts of a concentrated portfolio suffer from the same problem at the same time, and correlations that looked comfortable in calm times converge toward one. A correlation matrix makes the same point for currency pairs: instruments that seem distinct often share one driver.
One clarification is needed. Home bias does not mean investing in bad instruments. The problem arises when good instruments are bought in excessive quantities simply because they belong to one's own country. Domestic stocks and bonds may be perfectly sound; the error is in the weight rather than in the selection.
How to Keep Home Bias in Check
Home bias can be prevented, and the first step is to look at the portfolio as a whole. Asking whether a single investment is sound is not enough. What matters is how much of the total wealth depends on the same country, the same currency and the same sectors.
A useful exercise is to compare the portfolio's geographic allocation with the weights of the global market. If a country represents a small share of world market capitalization but occupies half of the portfolio, the domestic concentration is strong, whatever the quality of the individual holdings. The weights of an all-country index are a ready-made benchmark for this comparison.
A second tool is the global fund or ETF. A single product can give exposure to hundreds or thousands of companies spread across many countries, without having to pick each market by hand. Understanding how an ETF actually works is the prerequisite: the wrapper is simple, but the index it tracks decides the exposure.
This does not mean eliminating domestic investments. An investor can consciously give the home country a weight above its global share, for tax reasons, to match future expenses in the home currency, or because of specific knowledge of certain companies. What matters is that the tilt is a deliberate choice rather than the residue of familiarity.
Non-financial assets belong in the calculation as well. Real estate, a family business and labor income are already part of the overall geographic exposure. An investor whose salary and home are both tied to the domestic economy has a reason to hold less of it in the securities portfolio, not more.
Finally, periodic rebalancing keeps the allocation honest. If the home market has had a strong run and its weight has grown beyond the target, the portfolio can be brought back to the desired allocation. Rebalancing also works against the pull of the crowd: after a domestic rally, the familiar market is exactly where herd behavior pushes new money, and a rule that trims what has grown is the simplest defense.
Familiar Is Not the Same as Safe
Home bias is one of the few investing mistakes that nearly everyone makes and almost nobody notices, because it does not look like a decision. The research has measured it for more than three decades, and the numbers still show investors holding far more of their own country than its weight in the world would justify. The cost shows up in the worst moments: a domestic crisis hits the job, the house, the bank shares and the government bonds together. Looking at the whole picture, comparing it with the global map, using broad funds and rebalancing on a schedule are unglamorous habits, but they are what turns familiarity from a blind spot into a choice.
