What Is Home Country Bias?

Home country bias is the tendency for investors to overconcentrate in domestic assets. Most Japanese individual investors hold the vast majority of their wealth in Japanese stocks and yen-denominated deposits. Yet Japan's stock market accounts for only about 5-6% of global market capitalization. Allocating over 90% of your assets to Japan effectively ignores 94% of the world economy.

For further reading, books on diversification strategies can help you appreciate the power of combining assets with low correlation.

This bias arises from both psychological factors - the comfort of investing in familiar companies - and practical ones, such as easier access to Japanese-language information. From a rational allocation perspective, however, diversifying in proportion to global GDP or market capitalization is considered optimal.

The Risks of Concentrating in Japanese Stocks

Let's quantify the risks of a Japan-only portfolio. Japan's GDP represents roughly 4% of the global total (as of 2024), and while its stock market share is slightly higher, it is dwarfed by the United States, which accounts for about 60% of global market capitalization.

  • Demographic decline: Japan's working-age population has been shrinking since its 1995 peak and is projected to fall to about 70% of its current level by 2050. A declining labor force constrains economic growth.
  • Track record of prolonged stagnation: The Nikkei 225 peaked at 38,915 yen at the end of 1989 and took roughly 34 years to recover that level. Over the same period, the S&P 500 grew approximately 14-fold.
  • Natural disaster risk: Japan faces elevated risks from earthquakes, typhoons, and volcanic eruptions, all of which can severely impact economic activity and stock markets.
  • The flip side of currency risk: Holding only Japanese stocks means having no hedge against yen depreciation. If the yen weakens, investors without foreign assets see their real purchasing power decline.

Global Equity Index Composition and Regional Returns

The MSCI ACWI (All Country World Index) comprises roughly 2,800 stocks across 23 developed and 24 emerging markets. Regional weightings are approximately: United States 62%, Europe 15%, Japan 5%, emerging markets 10%, and others 8% (as of 2024).

Looking at regional returns over the past 20 years (2004-2024), U.S. equities delivered roughly 10.5% annualized, global equities about 8.5%, Japanese equities about 7.0%, and emerging-market equities about 6.5%. Because the best-performing region rotates over time, broad diversification offers more stable returns than betting on any single geography.

Managing Currency Risk

International investing introduces currency fluctuations. If you invest in U.S. stocks and the dollar rises 10% against the yen while the stock also gains 10%, your yen-denominated return is amplified. But if the yen strengthens 10% instead, your return in yen terms is nearly zero. Over the long run, however, currency movements tend to be neutral, and over horizons of 20 years or more, equity returns typically overwhelm currency effects.

Currency-hedged funds are an option, but hedging costs (roughly equal to the interest rate differential between Japan and the target country) can run 3-5% per year, often making unhedged funds more advantageous for long-term investors. Rather than fearing currency risk, combining time diversification with geographic diversification is the key to successful global investing. Try our simulator to see how different assumed return rates affect your projected asset growth.

Books on global equity index funds can help you understand how a single fund provides worldwide diversification.