A convertible bond is a corporate bond that carries an embedded right to exchange the bond for a fixed number of the issuer's shares. That single sentence hides the reason convertibles show up in interviews far more often than their share of issuance volume would suggest: they are the cleanest example in all of capital markets of an instrument that is genuinely two things at once, and candidates who can take one apart cleanly demonstrate that they understand both credit and equity. This guide explains what a convertible bond is, how the conversion premium and bond floor work, why issuers reach for equity-linked paper instead of straight debt or a follow-on share placement, and what actually goes wrong with the structure.
What Is a Convertible Bond?
Mechanically, a convertible bond is a straight bond plus a call option on the issuer's own stock. The investor receives a coupon and a promise of principal repayment at maturity, exactly as with any other corporate bond, but also holds the right to hand the bond back and receive shares instead. Because that option has value, the investor accepts a coupon far below what the same company would have to pay on non-convertible debt.
The economics are easiest to see with numbers. Take the worked example in our case study on pricing a convertible bond and splitting it into its debt and equity components: a mid-cap technology issuer places EUR 200m of five-year convertible bonds at par, with a 1.50% annual coupon, at a time when its comparable straight debt yields 6.00%. The company saves 4.50% a year in cash interest, or EUR 9.0m pre-tax. That saving is not charity. It is the price investors are willing to pay for the conversion right.
Four terms define the instrument, and interviewers expect all four by name:
| Term | What It Means | Example Value |
|---|---|---|
| Conversion Premium | How far above the reference share price the conversion right is struck | 30.0% |
| Conversion Price | Reference price grossed up by the premium; the effective price at which shares are sold | EUR 52.00 |
| Conversion Ratio | Number of shares each bond converts into; par divided by conversion price | 1,923.08 shares |
| Parity (Conversion Value) | Conversion ratio multiplied by the current share price | EUR 76,923 (76.9% of par) |
Notice that parity at issue sits well below the EUR 100,000 par value. That is by design. A convertible is deliberately issued out of the money, because the whole point of the conversion premium is that the issuer only ends up selling stock if the stock performs.
The Conversion Premium: The Term Everything Turns On
The conversion premium is the single most negotiated term in an equity-linked deal, and it is where the tension between issuer and investor lives. A high premium means the issuer gives away less equity, but it also means the option is further out of the money, so investors demand a higher coupon to compensate. A low premium means a cheap coupon but more eventual dilution. Typical premiums cluster between 20% and 40% for investment-grade-ish corporate issuers, with growth names and volatile stocks able to push higher, because volatility makes the embedded option more valuable.
The relationship to implied volatility is worth internalising, because it explains most of what looks arbitrary about convertible pricing. An option on a stock that moves a lot is worth more than an option on a stock that barely moves. So a company whose shares swing 45% annualised can sell a 35% conversion premium and still pay only 1% in coupon, while a stodgy utility might have to settle for a 20% premium and a 3% coupon on otherwise identical terms. When you read that a convertible "priced at the investor-friendly end of the range," it usually means the bookrunners had to concede either premium or coupon because demand was thinner than hoped.
A second driver is the credit spread. The wider the issuer's spread, the lower the present value of the bond component, and the more of the total price has to be carried by the option. This is why convertible pricing cannot be separated from credit analysis, and why the same discipline that applies to comparing investment grade and high yield issuers on ratings, covenants and spreads applies here too.
The Bond Floor: Where the Downside Protection Comes From
The bond floor, sometimes called the investment value or straight value, is what the instrument would be worth if the conversion right were stripped away entirely. You calculate it by discounting the convertible's own coupons and principal at the yield the issuer would pay on comparable non-convertible debt.
In the example above, EUR 1,500 of annual coupons and EUR 100,000 of principal, discounted at 6.00% over five years, give a bond floor of EUR 81,044, or 81.0% of par. Since the bonds were issued at 100, the residual EUR 18,956 — 19.0% of par — is the implied value of the embedded conversion option.
That split is the heart of the instrument. It produces the asymmetric payoff convertibles are famous for: limited downside because the bond floor should hold as long as the issuer stays solvent, and open-ended upside because the option participates in any share price appreciation above the conversion price. Marketing materials describe this as "equity upside with bond-like downside," and for long stretches of a market cycle it genuinely behaves that way.
The catch is that the floor is not fixed. Discounting the same cash flows at 9.00% instead of 6.00% drops the floor to EUR 70,828, more than ten points lower. Credit spreads widen precisely when the equity story is deteriorating, so in a genuine stress scenario the option value and the debt value fall together instead of offsetting each other. Anyone who has worked through a distressed capital structure and a debt-for-equity swap will recognise the pattern: the protection thins out exactly when it is needed. If the mechanics of discounting bond cash flows are not yet second nature, it is worth reviewing why bond prices fall when interest rates rise, and how duration and convexity work before attempting convertible questions.
Why Do Issuers Choose Convertible Bonds?
There are three reasons a treasurer will give, and a good answer covers all three rather than stopping at the coupon saving.
Selling Equity Forward at a Better Price
A follow-on equity placement today would price at or below the current EUR 40.00 share price, typically after a placement discount of a few percent. The convertible effectively sells the same shares at EUR 52.00. If the stock performs and the bonds convert, the issuer has raised equity 30% above where the market would have taken it. That is a materially better outcome for existing shareholders, and it is the argument that carries the most weight in a board discussion.
Cutting the Cash Interest Bill
The 4.50% coupon saving on EUR 200.0m is EUR 9.0m a year pre-tax and EUR 6.75m after tax at a 25% rate. For a company with real growth ambitions but thin near-term cash generation, that difference can be the gap between funding a capital programme and not funding it. It also protects credit metrics: interest coverage looks dramatically better on a 1.50% coupon than on a 6.00% one, which matters for anyone running the kind of debt capacity and covenant serviceability analysis a lender would perform.
Signalling
Equity issuance is read by the market as management saying the shares are fully valued, and share prices routinely fall on the announcement of a follow-on. A convertible sends the opposite signal: management is willing to sell stock, but only at a 30% premium, which implies they expect to get there. The signalling effect is real but modest, and it should not be oversold in an interview.
There is also a class of issuer for whom convertibles are less a choice than a necessity. Companies without an investment-grade rating, without a public bond curve, or with a shareholder base unwilling to absorb immediate dilution often find the equity-linked market is the only deep pool of capital available at a tolerable price. That is a different conversation from the one about senior, mezzanine and PIK tranches in a leveraged structure, where the sponsor is optimising a capital stack rather than solving an access problem, but the underlying logic of paying for flexibility is the same.
What It Actually Costs: The Honest Accounting
The temptation is to present a convertible as cheap money. It is not. Over five years the EUR 200.0m issue saves EUR 45.0m in pre-tax interest and hands investors roughly EUR 37.9m of option value at issue. The instrument is cheap on cash and expensive on equity, and the second half of that sentence is what separates a good answer from a superficial one.
Full conversion creates 3,846,154 new shares on a 100.0m base, or 3.70% of the enlarged share count. Compare that with raising EUR 200.0m at EUR 40.00 today, which would create at least 5.0m shares and dilute holders by roughly 4.8% immediately with no performance condition attached. The convertible dilutes less, and only conditionally — but the dilution is not free, and it does not wait for actual conversion to show up in the numbers.
Under the if-converted method, the underlying shares enter diluted earnings per share as soon as the instrument is dilutive: you add the after-tax coupon back to net income and add the full share count to the denominator. This differs from the treasury stock method used for options and warrants, a distinction covered properly in our guide to diluted EPS under the treasury stock and if-converted methods. Candidates who blur the two are usually the ones who have memorised a formula rather than understood a mechanism, and the diluted share count case is the fastest way to fix that.
Convertibles in the Enterprise Value Bridge
An unconverted convertible is debt. Add its face value, or its market value if it trades materially away from par, to net debt alongside every other borrowing when bridging from equity value to enterprise value. Once it is comfortably in the money, most practitioners switch treatment: remove the principal from debt and add the conversion shares to the share count, because that is the outcome the market is already pricing.
The one thing you must never do is both. Carrying the EUR 200.0m as debt and the 3.85m shares in the count double-counts the instrument and inflates enterprise value by roughly the size of the issue. If the bridge itself is shaky, work through the full enterprise value to equity value bridge including minorities, associates and pension deficits, or start from the conceptual explanation of the difference between enterprise value and equity value.
Who Buys Convertible Bonds?
The investor base is unusual and shapes pricing more than most candidates realise. Three groups dominate:
- Convertible arbitrage funds. They buy the bond and short a delta-equivalent number of shares, isolating the volatility and credit exposure while hedging out directional equity risk. They are price-sensitive to the option component and will simply not participate if the convertible prices rich to their model value.
- Outright convertible funds. Long-only managers who want the asymmetric payoff without hedging. They care more about the equity story and the bond floor than about implied volatility.
- Crossover credit and equity funds. Opportunistic buyers who appear when a specific name interests them, and disappear otherwise.
The arbitrage community's presence explains a phenomenon that puzzles issuers: a company's shares often fall on the announcement of a convertible, because arb funds are shorting stock to establish their hedge on day one. That pressure typically reverses, but it makes the announcement window uncomfortable, and it is one reason issuers frequently pair a convertible with a share buyback.
When Convertibles Go Wrong: The Busted Convertible
A convertible is described as busted when the share price has fallen so far below the conversion price that the option is effectively worthless and the bond trades purely on its credit merits. If the technology issuer's shares halved to EUR 20.00, parity would collapse to roughly EUR 38,462, or 38.5% of par, and the bond would trade near its floor — which would itself have fallen, because a halving share price rarely leaves the credit spread untouched.
Ownership rotates when this happens. Arbitrage funds, who need volatility and delta to earn a return, exit. High yield and distressed credit investors buy in, because from that point the only question that matters is whether the principal gets repaid at maturity. For the issuer it is the worst outcome available: the conversion that would have retired the debt in shares never arrives, and the full principal must be refinanced in cash, usually at a coupon several times the original 1.50%. That refinancing conversation looks a great deal like the one facing a leveraged borrower approaching a maturity wall, and the same analytical toolkit applies.
Convertibles, IPOs and the Wider Capital Markets Toolkit
Convertible bonds sit in the same product suite as follow-on offerings, accelerated bookbuilds, rights issues and IPOs, and an ECM interview will often move between them. A candidate who can explain why an issuer chose a convertible rather than an accelerated bookbuild, and can then talk sensibly about the full IPO process from kick-off to lock-up expiry or about IPO pricing, the greenshoe and aftermarket stabilisation, is demonstrating that they see the product set as a menu rather than a list of memorised definitions.
The same is true on the credit side. Convertible pricing depends on the issuer's straight-debt yield, which depends on rating, leverage and coverage — the exact material covered in the comparison of high yield and investment grade bonds. And the discount rate that produces the bond floor is a cousin of the cost of debt input in the weighted average cost of capital. Nothing in capital markets is genuinely standalone, and convertibles are the instrument that makes that most obvious.
The Short Version
A convertible bond is a straight bond plus a call option on the issuer's shares. The conversion premium determines how far out of the money that option starts; the bond floor, calculated by discounting the cash flows at the issuer's straight-debt yield, determines how much downside protection it offers; and the difference between the issue price and the floor is what investors are implicitly paying for the equity upside. Issuers use convertibles to sell equity forward at a premium, to cut the cash interest bill, and to avoid the negative signal of a straight equity placement — accepting in exchange a real, quantifiable transfer of option value and a conditional claim on their share count.
If you want to see all of that in numbers rather than words, the convertible bond case study walks through the conversion price, conversion ratio, parity, bond floor, implied option value, after-tax interest saving and dilution in sequence, with the follow-up questions an interviewer is most likely to ask next.