Stocks and Bonds Are Moving Together. That Weakens a Classic Safety Net
Global equities and government bonds had a rolling 36-month correlation of about 0.59 at the end of September 2026. Reuters
The estimate covers a three-year window on global benchmarks. It keeps stock-bond co-movement in positive territory.
On February 18, 2026, the International Monetary Fund published analysis titled "Stock-Bond Diversification Offers Less Protection From Market Selloffs". IMF
Historically, when stocks fell, investors sought safety in bonds, and bonds rallied, cushioning losses and stabilizing portfolios. That description formed the starting point for the Fund's analysis.
Analysts noted in September 2026 that a positive correlation between stocks and bonds emerged after the COVID-19 pandemic-induced inflation shock. Reuters
The stock-bond correlation tends to turn positive when inflation, the broad rise in prices, runs high, usually around 2.7%, except in recessions. Reuters
The broader context here is familiar to multi-asset investors. Correlation measures how tightly two assets move together. When it stays positive, bonds stop offsetting stock-market exposure in falls. A mixed portfolio swings more for the same stock holding, past-based diversification math overstates the smoothing, and automatic rebalancing buys stocks into weakness without the usual lift from bonds.
In my view, persistence matters more than the level. A 36-month window moves slowly, so this points to a shared pull from inflation and rate expectations rather than a brief risk-on spell. When inflation drives both legs, the extra return demanded for long bonds and for stocks moves together, bonds offer less portfolio protection, and assumptions rooted in the low-inflation years understate joint falls.
Looking at what this means for risk practice, the issue is measurement, not just allocation. History-based averages carry the inflation regime forward. Planners need separate paths for demand shocks and supply shocks, because bond compensation and stock valuations respond differently in each. That decides whether bonds act as ballast or amplifier, and estimates tied to inflation and growth give a cleaner read than broad averages.
