Week 46 Day 2: The Two-Fund Portfolio: U.S. Stocks and Bonds

Portfolio setup: 80% VTI + 20% BND. Total expense ratio: 0.03%. Annual rebalancing: sell the overweight fund, buy the underweight fund, until you are back at 80/20. Time required: 30 minutes per year. Expected return: approximately 8-9% long-term. This portfolio outperforms the majority of professionally managed portfolios over 10+ year horizons.

Why two funds is enough: (1) VTI holds approximately 4,000 U.S. stocks, covering 99%+ of the U.S. stock market by market cap. You own Apple, Microsoft, small-cap companies, REITs, growth, value -- everything. One fund = total U.S. equity diversification. (2) BND holds approximately 10,000 U.S. investment-grade bonds (government and corporate). One fund = total U.S. bond diversification. (3) Two funds = total U.S. market exposure. The ONLY thing missing is international stocks (covered by VXUS in the three-fund portfolio). Historical performance (1987-2024): 80/20 VTI/BND: approximately 9.5%/year, max drawdown -37%. 60/40 VTI/BND: approximately 8.3%/year, max drawdown -25%. 40/60 VTI/BND: approximately 7.0%/year, max drawdown -14%. Risk tolerance matching: Can you tolerate a 37% drop without selling? Go 80/20. Can you tolerate 25%? Go 60/40. Can you tolerate 14%? Go 40/60. Be honest. The 'best' allocation is the one you can STICK WITH through a crash, not the one with the highest expected return. The argument against adding international (VXUS): From 2010-2024, international stocks underperformed U.S. stocks by approximately 5%/year. Adding VXUS would have dragged returns significantly. BUT: from 2000-2009, international outperformed U.S. by approximately 3%/year, and from 1970-1989, international dramatically outperformed. Decades-long regimes alternate between U.S. and international dominance. The two-fund portfolio bets entirely on U.S. dominance continuing.

The two-fund portfolio (VTI + BND) is the simplest implementation of the mean-variance efficient portfolio. With only two assets, the efficient frontier is a simple curve parameterized by the stock/bond ratio. The optimal ratio depends on the investor's risk aversion coefficient (gamma): an investor with gamma = 2 (low risk aversion) should hold approximately 75-90% stocks, while gamma = 5 (moderate risk aversion) implies approximately 40-50% stocks. Empirically, the two-fund portfolio captures the 'market factor' (beta) which explains approximately 90% of the cross-sectional variation in portfolio returns (Fama and French, 1993). The remaining approximately 10% is explained by size, value, profitability, and investment factors, which the two-fund portfolio already holds implicitly (VTI is market-cap-weighted, so it includes all size and style segments in proportion to their market weights). The primary omission is international diversification. The case for including international stocks is: (a) the U.S. represents approximately 60% of global equity market cap (omitting 40% is a significant concentration), (b) international diversification reduces portfolio standard deviation by approximately 1-2% without reducing expected return (due to < 1.0 correlation), and (c) the home bias literature (French and Poterba, 1991; Coeurdacier and Rey, 2013) identifies systematic overweighting of domestic equities as a pervasive behavioral bias. However, the practical case for the two-fund portfolio is that the additional complexity of a third fund (even minimal) creates rebalancing and tracking-error temptations that may lead to behavioral errors whose cost exceeds the diversification benefit.