Why float matters in global bond beta: Lessons from Japan

• Global bonds have regained relevance as income has returned – but index construction increasingly shapes outcomes.

• Japan’s decades-long, extraordinarily loose monetary policy highlights the risks of treating all government bond markets as equally investible.

• Float‑adjusted indices are designed to tilt away from markets where size overstates accessibility.

Global bond exposure starts with index design

For portfolio constructors assessing fixed income allocations, global bonds have re‑entered the conversation with renewed credibility. The return of positive real yields has restored the asset class’s income potential, while diversification across issuers and regions remains a core portfolio objective. But as global bond beta regains relevance, how that exposure is constructed matters as much as why it is held.

Market‑capitalisation‑weighted indices remain the most common starting point. Yet in fixed income, market size does not always equate to accessibility. Central bank ownership, regulatory constraints and policy intervention can materially distort the portion of a bond market that is actually available to investors. Float‑adjusted indices attempt to address this by reducing the weight of securities that are effectively removed from the market, aiming to reflect the investible opportunity set more accurately.

Japan provides a timely and revealing example of why that distinction matters.

Japan’s bond market: Large, liquid – and constrained

Japan is one of the world’s largest bond markets, accounting for roughly 8-9% of traditional global aggregate indices¹. For decades, that weight appeared uncontroversial. But the Bank of Japan’s (BoJ’s) prolonged monetary intervention has fundamentally changed the structure of the Japanese government bond (JGB) market.

After years of quantitative easing and yield curve control, the BoJ owns approximately 43% of outstanding JGBs, dramatically reducing secondary‑market liquidity². At the same time, the central bank’s policy shift since 2024—including rate hikes, reduced asset purchases and the abandonment of explicit yield targets—has exposed a difficult trade‑off: allow yields to rise further, increasing government financing costs, or lean back towards accommodation and risk renewed currency weakness.

That dilemma is not theoretical. By the end of 2025, long‑dated JGB yields had climbed to levels not seen in decades, even as the yen remained under pressure (see chart below). With gross government debt near 230% of GDP and Japan heavily reliant on imported energy and food, inflation sensitivity to currency weakness remains high³. For investors, this creates a market where policy risk, duration risk and political risk increasingly overlap.

Conflicting pressures facing the Bank of Japan

Long-term yields rising despite currency weakness

Past performance is not a reliable indicator of future performance. Historical data shown are for illustrative purposes only and do not constitute a forecast.

Source: Bloomberg. Data are from 16 December 2012 (when Shinzo Abe’s Liberal Democratic Party won th general election) to 10 April 2026. Indices used: Japan 10-year government bonds = Generic Japan 10-year government bond; USD/JPY = USDJPY spot exchange rate. 

Why float adjustment changes the picture

Traditional bond indices treat Japan’s bond market as fully investible, regardless of how much of it is essentially locked away on the BoJ’s balance sheet. Float‑adjusted indices offer an alternative perspective: By excluding bonds that are effectively unavailable to investors, they reduce Japan’s weight meaningfully – while reallocating towards markets where yields are set more clearly by fundamentals.

The result is not a tactical call on Japan, but a structural one. 

• In a rising‑yield environment, Japan’s long‑duration profile amplifies downside risk: a 100‑basis‑point rise in JGB yields translates into materially negative returns at current duration levels.

• In contrast, a float‑adjusted global index naturally places more emphasis on markets such as the US and Europe, where bond supply, pricing and liquidity are more closely aligned with investor demand.

Importantly, this tilt has historically supported income generation. Higher average coupons, reinvested at higher yields, compound over time – and for bonds, income remains the dominant driver of long‑term total returns.

A broader lesson for global bond investors

Japan’s experience highlights a broader point: in fixed income, scale alone is a poor proxy for opportunity. Markets shaped by extraordinary policy support can look stable for long periods, only to become sources of volatility should that support be questioned or withdrawn.

For investors using global bond beta as a core exposure, float‑adjusted index methodologies are designed to recognise that reality. By anchoring allocations to accessibility rather than issuance alone, they aim to reduce unintended concentrations and better align exposure with investible risk.

As global bond markets adjust to a post‑QE world, Japan stands out not as an outlier but as a stress test. And it is precisely in these stress tests that index design shows its value.

Beyond float-adjusting, scaling global bond indices as an additional step can help reduce structural concentration in fixed income exposure. To learn more about what a float-adjusted and scaled global bond index exposure can bring to your portfolio, read our deep dive, Global bond beta unpacked: Investment case, index selection and implementation.

¹ Source: Bloomberg, as at 31 March 2026 the total weight was 8.2%.

² Source: CEIC Data, as at December 2025.

³ Source: International Monetary Fund, data projection for 2026 as at October 2025.