The Equity Risk Premium: Why Stocks Should Outperform Bonds (and When They Don't)

Every investor who holds equities over bonds is, implicitly, making a bet on the equity risk premium (ERP). The ERP is the additional return that investors demand — and have historically received — for holding equities rather than risk-free government bonds. It is the compensation for the volatility, uncertainty, and occasional catastrophic losses that equities deliver relative to government debt.

Understanding the ERP — what determines it, how it has varied, and what it implies for current equity valuations — is essential background for any investor making strategic asset allocation decisions.

Defining the Equity Risk Premium

The ERP is typically defined as:

Expected equity return – Risk-free rate = Equity risk premium

The risk-free rate is usually taken as the yield on short-term government bonds (UK gilts, US Treasuries). The expected equity return is harder to measure — it can be estimated historically (realised ERP) or prospectively (implied ERP).

Historical (realised) ERP: Over the very long run, UK equities have returned approximately 5–7% per annum in real (inflation-adjusted) terms, while UK gilts have returned approximately 1–2% real. This implies a historical realised ERP of roughly 3–5% per annum. Global data from the Credit Suisse Global Investment Returns Yearbook (now UBS) shows similar results across most developed markets over 100+ years.

Implied (prospective) ERP: The implied ERP can be estimated by inverting the current price-to-earnings ratio (earnings yield) and subtracting the current risk-free rate. If the FTSE 100 earnings yield is 6% and 10-year gilts yield 4.5%, the implied ERP is approximately 1.5% — below the long-run historical average. If gilt yields fall or equity earnings yields rise, the implied ERP widens.

The Equity Risk Premium Puzzle

Economists have long noted what they call the "equity premium puzzle" — the historical ERP appears too large to be explained purely by rational risk aversion. If investors were as risk-averse as the ERP implies, they would demand much higher premiums for other risks as well, which they do not.

Several explanations have been proposed:

• Survivorship bias: The strong historical US and UK equity returns partly reflect that these were among the most successful economies of the 20th century. Countries that experienced world wars, hyperinflation, or political upheaval performed dramatically worse.
• Rare disaster risk: Investors price in the possibility of severe, low-probability outcomes that have materialised in some markets (Germany, Russia, Argentina) even if they have not yet materialised in the UK or US.
• Behavioural factors: Loss aversion makes investors demand higher compensation for equity volatility than pure expected utility theory would suggest.

The puzzle's resolution does not materially change the practical case for equities in a long-term portfolio — a premium does appear to exist and to persist — but it does suggest that the full historical premium may not be replicable prospectively.

Factors That Drive the ERP

The ERP is not fixed. It varies over time based on:

Economic uncertainty: When the economic outlook is highly uncertain (crisis, pandemic, deep recession), investors demand a higher ERP — equities must be cheaper to compensate for greater risk. This is why equity valuations tend to be depressed at the bottom of recessions and why buying equities in periods of high uncertainty has historically produced above-average subsequent returns.

Interest rates: As risk-free rates rise, the implied ERP narrows if equity prices do not fall to compensate. This was the mechanism behind the 2022 equity market correction: US Treasury yields rose from 1.5% to 4.5%, dramatically reducing the implied ERP — forcing equity prices to fall to restore an adequate premium.

Corporate earnings expectations: If investors expect corporate profits to grow strongly, the implied forward ERP may be more attractive than the current ERP based on trailing earnings. Conversely, earnings disappointments compress the ERP.

Market sentiment and risk appetite: In periods of investor euphoria — late 1990s tech bubble, 2021 SPAC and meme stock mania — equity prices rise to levels where the implied ERP is very low or even negative. This historically precedes poor forward returns.

Inflation regime: In high-inflation environments, nominal equity returns may appear adequate but real returns (after inflation) are eroded. The real ERP matters as much as the nominal premium.

Estimating Today's ERP

As of mid-2026, assessing the current implied ERP requires looking at:

• UK (FTSE 100) earnings yield: Approximately 6–7% (based on trailing earnings), implying an ERP over 10-year gilts of roughly 1.5–2.5%.
• US (S&P 500) earnings yield: Significantly lower — US equity markets trade at premium valuations reflecting tech sector growth expectations. The implied US ERP using current CAPE (above 30) is historically among the narrowest in a century.
• Global ex-US equities: Japan, Europe, and EM markets trade at lower valuations, implying wider ERPs — suggesting potentially better prospective returns outside the US.

These are indicative estimates. The actual forward ERP depends on earnings outcomes that cannot be known in advance. Historical research by Damodaran at New York University shows that the implied ERP has ranged from negative (during the 1990s bubble peak) to above 8% (during the 2009 crisis trough). Current levels suggest US equities offer below-average prospective return premia; international developed and some EM markets look more attractive on this basis.

The ERP and the Case Against Equities

While the long-run ERP justifies holding equities in most long-horizon portfolios, there are conditions under which the ERP may not materialise:

Extended periods: Equities have delivered below risk-free returns over 10–15 year periods in the past. A US investor who bought in 2000 at peak valuations received zero real returns until 2013. A Japanese investor buying the Nikkei 225 at its 1989 peak waited over 30 years to break even in nominal terms.

Individual country risk: The long-run ERP is a global diversified average. Individual countries have seen permanent capital impairment — Soviet bonds, pre-revolution Russian equities, Zimbabwean equities, Argentine government bonds. Diversification across geographies reduces (but does not eliminate) this risk.

Valuation entry point: The single most important determinant of 10-year prospective equity returns is the valuation at which equities are purchased. Buying at a 40x CAPE dramatically increases the probability of a poor 10-year outcome relative to buying at a 10x CAPE.

Practical Implications for HNW Investors

Maintaining equity exposure across full cycles

The ERP is only earned by staying invested through periods of poor returns. Investors who exit equities during drawdowns and re-enter after recovery systematically underperform. The long-run premium accrues to the patient investor — not the tactical timer.

Geographic diversification of ERP sources

Concentrating equity exposure in one market (say, 100% US equities) concentrates all the ERP risk in one valuation level and economic cycle. A globally diversified equity portfolio — MSCI World or MSCI ACWI — provides access to the ERP across 40+ markets simultaneously, reducing dependence on any single market's valuation cycle.

Adjusting equity weight to risk tolerance, not market outlook

The theoretical optimal equity allocation is determined by an investor's ability to sustain drawdowns, not by market timing. An investor who genuinely needs 80% of their capital within five years cannot afford the downside risk of full equity exposure, regardless of how attractive the ERP may appear.

Tilting toward higher-implied-ERP markets

For investors willing to accept tracking error against a market-cap weighted global index, overweighting markets where the implied ERP is higher (currently: international developed, certain EM markets vs US equities) is a rational, evidence-grounded valuation tilt — distinct from market timing.

Alternatives to equity ERP

For investors who cannot sustain full equity volatility, other risk premia exist — the credit risk premium (corporate bonds over gilts), the illiquidity premium (private equity, private credit), and the term premium (long-duration bonds over short-duration). Combining multiple risk premia in a portfolio can construct similar long-run expected returns with different risk profiles.

Compliance Note

The equity risk premium is an expectation based on historical evidence, not a guarantee of future returns. Equities can and do deliver negative returns over extended periods. The implied ERP is sensitive to interest rate assumptions, earnings expectations, and market conditions, and can change rapidly. Past performance of equity markets is not a reliable guide to future performance. This guide is educational and does not constitute personal financial advice. Investors should seek qualified advice before making any asset allocation decisions.

How Global Investments Can Help

Global Investments advises internationally mobile HNW clients on strategic asset allocation — including the appropriate level of equity exposure for their circumstances, horizon, and risk tolerance. We incorporate valuation analysis, implied ERP estimates, and macroeconomic context into our portfolio construction process, helping clients earn the equity premium over time while managing downside risk appropriately. Contact our team to discuss your equity allocation.