Convertible Bonds

How it works

The issuer sells a bond carrying a stated coupon along with a conversion ratio: a fixed number of shares the holder can receive per bond of face value. Dividing face value by that ratio gives the conversion price, the effective share price at which the bond converts. The conversion premium measures how far the stock must climb above its price at issue before converting becomes worth more than simply holding the bond to maturity.

Because that conversion right is a call option with real value, the issuer can offer a lower coupon than it would on comparable straight debt. The coupon discount is the price the buyer accepts for holding the option. Most convertibles sit as senior unsecured debt; some are subordinated. Either way they rank above common and preferred equity and below secured lenders in a bankruptcy.

Issuers frequently retain a call provision, often gated by a soft-call trigger requiring the stock to trade above a multiple of the conversion price for a run of consecutive days. A call lets the issuer force conversion and end the option early. Investors, in turn, may hold put dates: specified points at which the bond can be sold back at face value, which shortens the effective maturity and functions as real credit protection. Change-of-control clauses typically add make-whole shares from a table published in the indenture if a takeover happens early in the bond's life, compensating for option value lost.

How a convertible behaves shifts with the stock. A busted convertible trades on credit alone because conversion is far out of the money; a balanced convertible responds to both credit and equity moves; an equity-sensitive convertible tracks the shares closely. Mandatory convertibles remove the holder's choice, converting automatically at maturity in exchange for a higher coupon. Bank contingent convertibles, or AT1/CoCo securities, are a separate instrument: they convert or are written down when a regulatory capital trigger is breached, not at the holder's discretion.

What it pays

A convertible pays a stated coupon on face value, usually semi-annually, and that coupon typically sits below what the same issuer would pay on non-convertible debt of similar maturity. The size of that discount is set by the volatility of the underlying stock, the conversion premium, the bond's tenor, and the issuer's credit spread: more volatility and a smaller premium mean a richer option and a lower coupon. Some convertibles are issued at a discount to face or as zero-coupon accreting instruments, so return arrives as accretion toward face value rather than as cash interest.

Total return runs on two engines simultaneously: the coupon stream, and the changing value of the embedded conversion option as the shares move. Converting is the holder's decision except in mandatory structures or when the issuer exercises a call, at which point converting is usually the only sensible response left. Convertible mutual funds and ETFs pool coupons across a portfolio of issues and pass them through net of the fund's expense ratio.

Yield is quoted two ways: yield to maturity and yield to the nearest put date. Because puts are exercised often when the stock has languished, yield to put is frequently the more meaningful figure for gauging realistic return.

Costs and taxes

Individual convertibles trade over the counter, so the cost of entry and exit is a dealer's bid-ask spread in a market with limited pricing transparency. Fund and ETF holders instead pay an ongoing expense ratio and avoid dealing with individual bond spreads.

Coupon interest is ordinary income under US federal tax rules. A bond issued at a discount to face carries original issue discount, which must be accrued into taxable income each year regardless of whether cash is actually paid out.

Converting into the issuer's shares under the bond's own terms is generally a nonrecognition event: no gain or loss is realized at conversion, the bond's basis carries over to the stock received, and the holding period generally tacks on for purposes of long-term treatment. Selling the bond outright instead of converting produces capital gain or loss, subject to the market discount and OID rules that can recharacterize part of that gain as ordinary income.

Some convertibles are structured as contingent payment debt instruments, which alters the accrual pattern and can turn gain on sale into ordinary income rather than capital gain; the prospectus specifies the intended treatment. Investors in convertible funds simply receive a 1099 reflecting the fund's own characterization of distributions, which removes conversion mechanics from the investor's personal tax return.

Liquidity and time commitment

Convertibles trade over the counter and liquidity varies enormously by issue. Large, recently issued convertibles trade with reasonable depth; small or seasoned issues can go days without a print. Convertible mutual funds and ETFs offer daily liquidity at the cost of a management fee and no say over which individual bonds the fund holds.

Stated maturities commonly run several years, but put dates and call provisions frequently end a bond's life well before that final date arrives. Holding individual convertibles is not a set-and-forget position: it requires tracking the conversion price against the stock, watching for call notices, and diarising put windows, since a missed window forfeits the protection it offered.

Convertible arbitrage funds, which buy the bond and short the underlying stock against it, make up a large share of the buyer base and shape both new-issue pricing and secondary market liquidity. Access to new issues is largely institutional, since most convertibles are placed initially under Rule 144A and only season into broader secondary trading over time.

How it goes wrong

The most direct failure is default. Convertible issuers skew toward unprofitable growth companies unable to place straight debt at a tolerable coupon, so credit risk is genuine, and recovery on unsecured paper in a bankruptcy can be thin. Short of default, a stock collapse leaves a busted convertible: a low-coupon bond of a stressed company, with the equity upside gone and the income never having been competitive in the first place.

On the other side, a strong stock invites an issuer call, which caps upside near conversion value and forces an immediate decision about what to do with the shares received. Conversion itself presses on the stock through dilution, and heavy convertible issuance has weighed on some names for years afterward.

Liquidity can vanish in stress. Convertible arbitrage unwinds have historically forced simultaneous selling across the market, widening spreads far beyond what the underlying credit alone would justify. On the administrative side, a missed put date leaves the holder stuck in a bond that would otherwise have been redeemed at face value, a loss that comes purely from a missed deadline rather than markets moving.

Confusion between corporate convertibles and bank contingent convertibles has cost investors before. The 2023 Credit Suisse resolution, in which AT1 instruments were written down to zero while shareholders retained some value, illustrated how differently a regulatory-trigger CoCo behaves compared with an ordinary corporate convertible bond.