The Equity Risk Premium: Why Stocks Must Outperform Bonds to Attract Capital
The equity risk premium (ERP) is the excess return that investors expect from stocks over risk-free government bonds — calculated as expected stock market return minus the risk-free rate (typically the 10-year Treasury yield). When bond yields are low, the ERP is high and money flows to stocks. When bond yields rise, the ERP compresses and stocks become less attractive relative to the safety of bonds.
The equity risk premium (ERP) is the additional return that investors demand for holding stocks instead of risk-free government bonds. It is the central mechanism determining whether capital flows into equities or fixed income. ## Formula ERP = Expected Stock Market Return − Risk-Free Rate The risk-free rate is typically the 10-year Treasury yield for long-term calculations. The expected market return is harder to measure — it can be estimated from historical averages (~7-10% nominal for US equities), earnings yields, or forward-looking models. ## How It Drives Markets When the ERP is high (e.g., expected stock return 7%, bond yield 1%, ERP = 6%), stocks are very attractive relative to bonds. Capital flows into equities, pushing prices up. This characterized the 2009-2021 era, when near-zero interest rates made bonds unappealing and equities were the only place to earn meaningful returns. When the ERP compresses (e.g., expected stock return 7%, bond yield 5%, ERP = 2%), the extra reward for taking stock market risk shrinks. Investors can earn 5% safely in bonds, so the bar for stocks gets much higher. This characterized 2022-2023, when rising rates caused a ~20% S&P 500 decline as capital rotated to fixed income. ## The 10-Year Treasury as Benchmark The 10-year Treasury yield is often called the most important number in finance because it serves as the baseline for: mortgage rates (banks add a risk premium on top), corporate borrowing costs, stock market valuations via the ERP, and virtually all risk-asset pricing. When the 10-year yield moves, everything else adjusts. ## Historical Context The long-run average ERP for US equities is approximately 4-6% above Treasury yields. Periods where it compressed below 2% (late 1990s, 2007) often preceded market corrections. Periods where it exceeded 6% (2009, 2020) often preceded strong equity rallies. How the Bond Market Controls Mortgages, Stocks, and Jobs Dollar Cost Averaging and Drawdowns: Why Market Drops Build Long-Term Wealth