What is a 60/40 portfolio?

A 60/40 portfolio holds 60% of its value in stocks and 40% in bonds, usually through broad index funds, and is rebalanced regularly to keep that split. For decades it has been the reference point for a balanced portfolio: the stocks provide growth, the bonds stability and income, and together they aim for most of the stock market's long-term return with noticeably smaller swings.

Why the mix works

The expected return of the portfolio is the weighted average of its two parts:

E[R_p] = 0.6 \, E[R_{\text{stocks}}] + 0.4 \, E[R_{\text{bonds}}]

Its risk is lower than the weighted average of the two volatilities, as long as stocks and bonds do not move perfectly together:

\sigma_p = \sqrt{0.6^2 \sigma_s^2 + 0.4^2 \sigma_b^2 + 2 \times 0.6 \times 0.4 \, \rho \, \sigma_s \sigma_b}

where $\sigma_s$ and $\sigma_b$ are the volatilities of stocks and bonds and $\rho$ their correlation.

A simple illustration

Assume stocks return 7% a year with 16% volatility, bonds 3% with 6% volatility, and their correlation is 0:

E[R_p] = 0.6 \times 7\% + 0.4 \times 3\% = 5.4\%

\sigma_p = \sqrt{0.36 \times 0.16^2 + 0.16 \times 0.06^2} \approx 9.9\%

The portfolio keeps more than three quarters of the stock return (5.4% of 7%) with around 60% of the stock volatility (9.9% of 16%).

How it has done

Over long periods, balanced 60/40 portfolios have delivered solid returns with drawdowns roughly half as deep as those of pure stock portfolios. The combination worked particularly well between 2000 and 2020, when bonds often rose while stocks fell.

2022 tested it: inflation and rapidly rising interest rates made stocks and bonds fall together, and many 60/40 portfolios lost around 15–20%, one of their worst years in decades.

Variations and limits

The split is a convention, not a law. Investors with long horizons often hold more stocks; those close to needing the money often hold fewer. 80/20 and 40/60 follow the same logic with a different balance of growth and stability.
The type of bond matters. The stabilizing role comes from high-quality government and investment-grade bonds; high-yield bonds behave more like stocks.
The correlation is not fixed. The mix relies on stocks and bonds not falling together. When inflation is the main risk, as in 2022, that protection can fail.
Rebalancing is part of it. Without rebalancing, the stock share drifts upward in good years and the portfolio slowly stops being 60/40.

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