Stock-Bond Correlation: Regime Shifts That Redefine Risk

For two decades the 60/40 portfolio worked because stocks and bonds were negatively correlated — bonds rose when stocks fell, cushioning drawdowns. That correlation flipped positive in 2022 and again in stress episodes, breaking the hedge. Traders who ignore regime shifts get caught using a hedge that no longer works.

The two regimes

Negative correlation (risk-off hedge). Bonds rally when equities sell off. This dominated 2000–2021. The driver was disinflation and credible central banks — when growth disappointed, rate-cut expectations lifted bonds while equities fell. Typical 90-day correlation: -0.3 to -0.6.

Positive correlation (simultaneous sell-off). Stocks and bonds fall together. This appears when inflation is high and volatile, or when fiscal dominance erodes bond credibility. In 2022, the S&P 500 fell 19% while the 10-year Treasury returned -17%. Correlation reached +0.6. Both legs of the 60/40 lost together.

What triggers the flip

The dominant variable is inflation volatility. When 1-year inflation breakevens swing more than 50 basis points month-over-month, the stock-bond correlation tends to turn positive. Growth shocks keep it negative; inflation shocks flip it positive. Central bank credibility matters: when policy is trusted, bonds are a hedge; when it is questioned, bonds become a risk asset.

How to track it

Compute a rolling 60-day correlation between S&P 500 daily returns and 10-year Treasury daily returns (use TLT or IEF for the bond leg). Below zero, bonds hedge equity drawdowns. Above +0.3, the hedge is broken — hedging equities with Treasuries adds risk rather than reducing it.

Adjusting exposure

• Negative regime: hold bonds as an equity hedge, size risk-on equity exposure normally.
• Positive regime: replace duration with cash or short-term T-bills for the defensive sleeve; consider VIX calls or managed futures for drawdown protection. Cut equity beta by 20–30%.
• Transition (correlation between 0 and +0.3): reduce position size, avoid leveraged carry, and wait for the regime to resolve.

Review the reading weekly. Regime shifts persist 6–18 months, so you do not need to react daily, but you must not ignore a multi-week move above +0.3.

The bottom line

Stock-bond correlation is regime-dependent. Negative under growth shocks and credible policy; positive under inflation shocks and fiscal stress. Track the 60-day correlation, and when it crosses +0.3, stop using long-duration bonds as an equity hedge and switch to cash or alternatives. A hedge that worked yesterday can become a second loss today.