The Portfolio Diversification Case
Bonds have historically served a critical function in diversified portfolios: they tend to perform well when equities perform poorly. During recessions and financial crises, central banks typically cut interest rates, which pushes bond prices up. At the same moment, equity prices often fall sharply. This negative correlation — when it holds — means a portfolio combining equities and bonds is smoother than either asset alone, reaching a given return target with less volatility than a pure equity portfolio would.
This relationship was robust and consistent from the mid-1980s through to the early 2020s — a period characterised by falling and then low inflation. In that environment, bonds were a reliable equity hedge. The 2022 experience challenged this pattern: rising inflation caused central banks to hike rates aggressively, causing both equity and bond prices to fall simultaneously. The 60/40 portfolio (60% equities, 40% bonds) had its worst year in decades. Whether the correlation between stocks and bonds remains negative in a higher-inflation world is now actively debated among portfolio managers.
Income and Liability Matching
Bonds pay predictable, scheduled cash flows — coupons and principal at maturity. For investors who need to generate income or match future liabilities, this predictability has great value.
Pension funds are the largest institutional bond holders, for this reason. A defined-benefit pension fund knows with reasonable precision the amounts it must pay to pensioners in each future year. By holding bonds whose cash flows match those payment obligations, the fund eliminates the risk that asset values will be insufficient when payments are due. This is liability-driven investing (LDI) — matching assets to liabilities through bond duration and cash flow timing.
For individual investors approaching retirement, bonds serve a similar function: providing predictable income and capital preservation as the need for reliable cash flow supersedes the desire for maximum growth.
Capital Preservation
In portfolios where protecting capital is paramount — endowments, foundations, or individuals near retirement — bonds (particularly high-quality government bonds) offer something equities cannot: a known repayment date and amount. A government bond held to maturity will return its face value, regardless of what interest rates do in between. This certainty is worth paying for when the consequences of a large loss are severe.
High-quality short-duration bonds are sometimes described as "dry powder" in an investment portfolio: assets that will hold their value in a market crisis, allowing the investor to redeploy capital into equities at depressed prices without being forced to sell at the worst moment.
The Interest Rate Risk Caveat
The benefits of bonds as a portfolio component come with an important caveat: duration risk. Longer-dated bonds fall significantly in price when interest rates rise. A pension fund or investor who holds long-duration bonds and then needs to sell before maturity can face large losses if rates have risen — as happened in the UK pension fund crisis of autumn 2022, when sudden rate rises created severe mark-to-market losses in liability-driven investment portfolios.
The appropriate duration for a bond allocation therefore depends on the investor's time horizon and their sensitivity to interim mark-to-market movements.