Convertible Bonds: Equity Upside with Fixed Income Protection
A convertible bond occupies a unique position in the investment universe: it is a bond that can become a share. This hybrid nature creates an asymmetric return profile that is structurally appealing — the investor participates in equity upside while retaining the bond's income and capital protection characteristics on the downside.
In theory, convertibles are positioned as the "best of both worlds." In practice, the asset class is more nuanced: the conversion option and the bond floor interact in complex ways, issuer quality matters enormously, and the protection offered by the bond structure depends critically on the issuer's creditworthiness. This guide explains the mechanics, the appeal, the risks, and how to incorporate convertibles into a diversified portfolio.
What Is a Convertible Bond?
A convertible bond is a debt instrument issued by a company that carries a standard coupon and maturity date — like any other bond — but with an additional embedded option: the holder can convert the bond into a specified number of the issuing company's shares, at a specified price (the "conversion price"), at or before maturity.
A typical convertible structure might look like:
- Issuer: a technology company
- Face value: £1,000 per bond
- Coupon: 2.0% per annum
- Maturity: 5 years
- Conversion price: £50 per share (30% above the share price of £38.50 at issuance, known as the "conversion premium")
- Conversion ratio: 20 shares per bond (£1,000 / £50 conversion price)
The investor holds this bond and receives 2.0% coupon annually. Over the five years, the share price may evolve in several ways:
If the share price rises above the conversion price (£50): the conversion option becomes valuable. When the share price reaches £60, the investor can convert the bond into 20 shares worth £1,200 — gaining £200 above the £1,000 par value. They participate in the equity upside.
If the share price remains below the conversion price: the investor holds the bond to maturity, receives the remaining coupons, and is repaid £1,000 at maturity — as long as the company has not defaulted. The "bond floor" — the present value of the bond's cash flows (coupons + par) — provides the downside protection.
If the issuer defaults: the bond floor disappears. The investor's recovery depends on the company's assets and the bond's seniority in the capital structure — typically senior to equity but subordinate to secured creditors.
The Asymmetric Return Profile
The appeal of convertibles is captured by the phrase "equity upside with bond downside." In aggregate, studies of convertible bond indices over long periods suggest they capture approximately 50–75% of equity market upside and only 30–50% of equity market downside.
This asymmetry arises from the option-like structure: when equities rise, the convertible's conversion option gains value and the bond performs more like equity. When equities fall, the conversion option loses value but the bond floor limits downside — the investor holds an instrument that pays known cash flows.
However, the asymmetry is not guaranteed in all environments:
Rising rate environments (2022): When interest rates rise sharply, the present value of the bond floor falls (higher discount rates reduce the PV of future cash flows). Simultaneously, many convertible bond issuers are growth/technology companies whose valuations fell as rates rose. In 2022, convertible bonds declined alongside equities as both the equity option value and the bond floor were impaired simultaneously. The "protection" was less than the historical averages suggested.
Default environments (2008): In the 2008 financial crisis, the bond floors of financial sector convertibles collapsed as credit risk spiked. Investors in convertibles issued by Lehman Brothers, Bear Stearns, and other distressed financials suffered severe losses — the bond floor is only as strong as the issuer's credit quality.
These experiences do not invalidate the long-term asymmetric return argument for convertibles, but they illustrate that the downside protection is conditional on credit quality and the interest rate environment.
The Conversion Premium and Delta
Two technical measures are important for assessing a convertible's characteristics:
Conversion premium. The percentage by which the conversion price exceeds the current share price. A 30% conversion premium means the share price must rise 30% before the conversion option is in the money. Higher premiums mean the bond behaves more like a straight bond (interest-rate sensitive, less equity-sensitive); lower premiums mean it behaves more like equity.
Delta. In options terminology, delta measures how much the convertible's price moves for a given move in the underlying share price. A delta of 0.5 means the convertible moves £0.50 for every £1 move in the share. Convertibles with low delta (near zero) are behaving as bonds; those with high delta (near 1.0) are behaving as equity. The "sweet spot" for the asymmetric return profile is convertibles with moderate delta (0.3–0.7), where both the bond floor and the equity upside are meaningfully contributing to the risk/return profile.
Who Issues Convertibles?
Convertible bonds are typically issued by companies that:
Have strong equity growth stories. The conversion option is only valuable if the share price rises significantly. Companies with compelling equity narratives can place convertibles at lower coupons (investors accept lower income in exchange for the upside option). This has historically made technology, healthcare/biotech, renewable energy, and high-growth consumer companies frequent issuers.
Want to reduce borrowing costs. Issuing a convertible at 2% rather than a straight bond at 5% reduces interest expense significantly. The company is effectively selling a call option on its own shares to reduce its debt servicing costs.
May not want to issue equity immediately. A company that believes its share price will rise would rather issue a convertible (sharing upside at a premium) than issue equity at the current price (which it considers undervalued).
Are at a growth stage with potentially limited access to cheap conventional debt. Smaller or higher-growth companies without investment-grade credit ratings can access capital at lower rates via convertibles than straight high-yield bonds.
The universe of convertible issuers therefore tends to be more growth-oriented, higher-risk, and more concentrated in technology and healthcare than the broader bond market — a fact investors must incorporate in their risk assessment.
The Global Convertible Bond Market
The global convertible bond market totals approximately $350–400 billion outstanding, with the US the largest market (approximately 60–65% of the global total), followed by Europe (approximately 15–20%) and Asia-Pacific.
Key indices include the FTSE Global Focus Convertible Index (formerly the Thomson Reuters/Refinitiv Global Focus index, renamed by LSEG in 2024) and the ICE BofA Global Convertible Index, which serve as benchmarks for the asset class.
Active managers dominate the convertible bond space — the complexity of the instruments (assessing credit quality, the option value, and the conversion delta simultaneously) makes skilled active management more defensible than in plain equity or investment-grade bond markets. Key managers include:
- Fisch Asset Management (Switzerland-based, one of the largest specialist convertible managers)
- Lazard Asset Management (Global Convertible strategies)
- Calamos Investments (US-focused, one of the pioneers of convertible bond investing)
- CG Convertibles (European specialist)
For UK investors accessing convertible bonds via listed UCITS vehicles, the SPDR FTSE Global Convertible Bond UCITS ETF (formerly branded SPDR Thomson Reuters/Refinitiv) provides passive exposure to the global convertible market, though the index-based approach captures the full universe including lower-quality, higher-risk issuers.
Convertible Bonds in a Portfolio Context
How do convertibles fit into a diversified portfolio? Several arguments support a modest allocation:
Diversification from traditional bonds. Convertibles have low correlation with investment-grade bonds over the long run — their return driver is equity performance, not interest rates. Adding convertibles to a traditional equity/bond portfolio can improve the risk-adjusted return profile.
Asymmetric return profile for risk-constrained investors. Investors who want some equity participation but cannot accept the full volatility of an equity allocation (pension trustees, foundations with return targets) have historically used convertibles to gain partial equity exposure with a theoretical floor.
A role in growth-oriented portfolios. For investors with a growth orientation who also want some downside ballast, convertibles provide a middle path between pure equities and pure bonds.
The cost of the option. The lower coupon on a convertible compared with a straight bond is not free — the investor is effectively paying for the conversion option through foregone income. In an environment where the equity option never becomes in the money (shares stay flat or fall), the investor is left holding a below-market-yield bond. Whether the option premium is fairly priced depends on the issuer's equity volatility and the conversion premium terms.
A typical convertible allocation in a balanced portfolio: 5–10% of total assets. This is sufficient to benefit from the asymmetric profile without creating significant concentration in a small and complex market.
How Global Investments Can Help
Convertible bonds offer a structurally interesting return profile that can complement traditional equity and bond allocations in sophisticated portfolios. However, the asset class requires careful manager selection, credit quality assessment, and an understanding of the option mechanics that is not required for plain equities or investment-grade bonds.
At Global Investments, we assess convertible bond exposure in the context of the client's overall portfolio, risk tolerance, and the current market environment. We identify appropriate fund managers or ETF vehicles for the desired risk/return profile and ensure that convertible allocations are appropriately sized and monitored.
Capital is at risk. Convertible bonds can fall in value due to rising interest rates, deterioration in the issuer's credit quality, or falling equity prices. The bond floor provides conditional, not absolute, protection. Past performance is not a reliable indicator of future results. This guide is for information purposes only and does not constitute financial advice.
This guide is for general information only and does not constitute financial advice or a personal recommendation. The value of investments can fall as well as rise and you may get back less than you invest. Past performance is not a guide to future returns. Tax rules, investment regulations, and the availability of specific investment vehicles change — always verify current rules and seek advice from a qualified independent financial adviser before making any investment decisions.