Convexity isn’t just a technical finance buzzword — it’s a key to understanding how your bond investments will behave as Australia navigates a shifting interest rate landscape in 2025. Whether you’re a seasoned portfolio manager or a retail investor looking to diversify, knowing how convexity works can help you make smarter decisions, manage risk, and potentially boost your returns.
What Is Convexity — and Why Should You Care?
At its core, convexity measures how the duration of a bond changes as interest rates move. While duration gives you a snapshot of how much a bond’s price will change with a 1% move in rates, convexity adds a second layer: it shows how that sensitivity itself changes as rates rise or fall.
- Positive convexity: Most vanilla bonds (like Australian government or investment-grade corporate bonds) exhibit positive convexity. This means their prices fall less when rates rise and rise more when rates fall — a win for investors.
- Negative convexity: Some securities (notably callable bonds or mortgage-backed securities) can exhibit negative convexity, where price gains are capped if rates fall, but losses aren’t limited if rates rise.
Why is this crucial in 2025? The Reserve Bank of Australia (RBA) has signalled a data-dependent approach to rate moves this year, with inflation still sticky and global risks in play. Bond price movements are increasingly non-linear, making convexity a vital risk metric.
Convexity in Action: Real-World Examples
Let’s say you own a 10-year Australian government bond. If the RBA unexpectedly cuts rates, the bond’s price will jump. But because of convexity, that jump is slightly larger than the basic duration calculation would predict. Conversely, if rates rise, the price falls — but not as sharply. This asymmetry works in your favour.
Compare this to a mortgage-backed security (MBS). When rates fall, homeowners refinance, and the MBS gets paid back early. Your upside is limited, but if rates rise, prepayments slow down, and you’re stuck with the bond at lower yields — classic negative convexity.
- Institutional portfolios: Major super funds now use convexity analysis to assess interest rate risk beyond duration, especially as regulatory rules (like APRA’s 2025 updates to capital requirements) demand more granular risk management.
- Exchange-traded funds (ETFs): Even retail investors in bond ETFs are affected. Funds tracking longer-duration benchmarks (e.g., Australian government bond ETFs) may see more pronounced price moves — and convexity explains why these moves aren’t always linear.
How to Use Convexity in Your Portfolio in 2025
The big question: how can you put convexity to work?
- Risk management: With rate volatility expected to persist in 2025, portfolios with higher positive convexity are better cushioned against sharp moves. This is especially important if you rely on bonds for capital stability.
- Bond selection: All else equal, investors may prefer bonds with higher convexity, especially in uncertain rate environments. However, higher convexity often comes at a cost (lower yield).
- Active strategies: Professional managers can use convexity to tilt portfolios, overweighting or underweighting securities as the yield curve changes shape — a relevant tactic as the RBA balances inflation, employment, and external shocks in 2025.
For example, if you expect rates to fall sharply, longer-duration and higher-convexity bonds could deliver outsized gains. If you think rates will rise or remain volatile, focusing on bonds with lower convexity (or even floating-rate notes) might make more sense.
2025 Policy Updates and Market Trends
This year, Australian regulators and market participants are paying closer attention to convexity:
- APRA’s 2025 capital rules now require more sophisticated interest rate risk modelling for banks and super funds, elevating the importance of convexity in stress tests and scenario planning.
- Bond ETF disclosures have improved, with major providers now including average portfolio convexity in their monthly reports, helping investors make more informed choices.
- RBA communications are highlighting the non-linear impacts of rate changes on household and institutional balance sheets, bringing convexity to the fore in monetary policy discussions.
In this environment, ignoring convexity could mean underestimating both risks and opportunities in your fixed-income allocation.
Conclusion: Make Convexity Part of Your 2025 Playbook
Convexity is more than a technical detail — it’s a practical tool for navigating Australia’s bond market in a year of shifting rates and policy updates. By understanding how convexity affects price moves, you can better manage risk, select the right bonds, and position your portfolio for whatever 2025 brings.
