Convertible Bonds

A convertible bond is a hybrid security combining a corporate bond with an embedded call option on the company's equity. The bondholder receives fixed coupons and principal like a regular bond, but can convert into a fixed number of shares at any time. Convertibles appeal to investors seeking equity upside with downside bond protection.

Key takeaways

• Convertible bonds have a fixed conversion ratio (e.g., 50 shares per $1,000 bond); the conversion price is the par value divided by the ratio
• The bond has a "floor" value equal to the straight bond value (what it would yield if not convertible); equity conversion has a "ceiling" (the stock price at conversion)
• Convertible investors trade bond income and protection for stock upside; the embedded equity option is typically worth 20–40% of the bond's value
• Convertibles are issued by growth companies and companies with weak credit that cannot access unsecured debt markets at reasonable rates
• The main risk is being "diluted" if the company converts the bond (forcing conversion into diluted equity), or being "called" if the issuer redeems the bond before conversion is accretive

Structure of a convertible bond

A convertible bond typically specifies:

Par value and coupon

• $1,000 par value
• 2.5% annual coupon (paid semi-annually)
• The coupon is lower than a straight corporate bond because the conversion option is valuable

Conversion ratio and conversion price

• Conversion ratio: Number of shares received per bond converted. Example: 50 shares per bond
• Conversion price: The effective price per share. Calculated as par value ÷ conversion ratio = $1,000 ÷ 50 = $20 per share
• The bondholder converts when the stock price exceeds the conversion price (plus accrued interest and a margin for transaction costs)

Conversion period

• Usually, conversion is allowed from issuance until a few days before maturity
• Some bonds have limited conversion windows

Callability

• Most convertible bonds are callable by the issuer at par (or par + accrued coupon)
• If the stock price rises above the conversion price, the issuer calls the bond to force conversion, eliminating the bondholder's upside beyond the call price

Other features

• Some convertibles have put options allowing the bondholder to redeem at par under specific conditions (similar to puttable bonds)
• Some have "capped conversions" where the total conversion value is limited

Why companies issue convertible bonds

Companies issue convertibles for several reasons:

Lower coupon, lower cost of capital

• A company that would pay 5.0% on straight debt can issue convertible at 2.5% because investors accept lower coupons in exchange for equity upside
• Example: Square Cash (Block) issued convertibles to fund growth at lower immediate cost than straight debt

Equity-like financing without immediate dilution

• Convertibles are equity-like (they can convert to equity) but are debt until conversion
• They raise capital without immediately diluting existing shareholders
• If the stock price does not reach conversion prices, the company has cheap debt that never converts

Regulatory capital treatment

• In some jurisdictions, convertibles count toward capital requirements for banks and insurers (they are equity-like for regulatory purposes)
• This allows capital-constrained companies to raise funds without explicit equity offerings

Flexibility

• A company can issue convertibles to hedge equity volatility without explicit equity hedging contracts

Bridge financing

• Distressed companies with weak straight debt ratings can issue convertibles because equity upside compensates investors for credit risk
• The company can later refinance at straight debt rates if the business improves

Valuation: Bond floor and conversion value

The value of a convertible bond is the maximum of:

1. Straight bond value (the value if it were a non-convertible bond)
2. Conversion value (the stock price × conversion ratio)

Plus a premium for the optionality.

Example:

• Convertible bond: 2.5% coupon, $1,000 par, 2045 maturity, 50 shares conversion ratio
• Current stock price: $15 per share
• Current risk-free rate: 5% (assuming the company is investment-grade)

Straight bond value: The bond's coupons and principal, discounted at 5.5% yield (50 basis points for credit spread over Treasuries):

• Present value of $1,000 par + semi-annual $12.5 coupons discounted at 5.5% ≈ $880

Conversion value: $15 stock price × 50 shares = $750

Convertible bond price: Typically trades at a premium to both, perhaps $920 (the option value adds roughly 4–5%). The $920 reflects:

• $880 straight bond floor
• Plus an option value (the right to convert if the stock rises above $20)

Now suppose the stock rises to $25 per share:

• Straight bond value: Still $880 (bonds don't benefit from stock price appreciation, only cash flows)
• Conversion value: $25 × 50 = $1,250
• Convertible bond price: Approximately $1,250 (the bondholder would convert into $1,250 of equity value or demand redemption)

The bondholder participates in the stock's upside but is protected by the bond floor on the downside.

Conversion premium and dilution

When the convertible is issued, the conversion price is set above the current stock price. The conversion premium is the percentage above the current price:

• Current stock price: $18
• Conversion price: $20
• Conversion premium: ($20 − $18) / $18 = 11.1%

The premium protects the company: the stock must rise above $20 for conversion to occur. If the stock is $19, the bondholder won't convert (they'd rather get par at maturity). Premiums typically range from 20–40% at issuance.

Dilution occurs when conversion happens. If the company has 100M shares outstanding and converts 10M shares of convertible bonds:

• Pre-conversion shares: 100M
• Post-conversion shares: 110M
• Dilution: 10% (existing shareholders' percentage ownership drops by 10%)

A company that issues convertibles with expectation that they will convert is effectively raising equity, but with a time delay (deferring the dilution until the stock appreciates).

Call provisions and forced conversion

Most convertible bonds are callable at par by the issuer. If the stock price rises significantly above the conversion price, the issuer calls the bonds to force conversion:

• Stock rises to $30, conversion value is $1,500
• Issuer calls bond at par ($1,000)
• Bondholder must convert into 50 shares (worth $1,500) or let the issuer redeem
• Effectively, the issuer captures the upside above par

The call provision caps the bondholder's upside. If the bond is callable at par and the conversion price is $20, the bondholder's maximum upside is $1,000 + accrued interest, even if the stock rises to $100.

This is similar to regular callable bonds and makes convertibles less attractive to equity-focused investors.

Risks specific to convertible bonds

Credit risk: If the company's credit deteriorates, the straight bond floor falls. A convertible issued at par with an $880 bond floor might see that floor fall to $750 if credit spreads widen. The bondholder loses downside protection.

Equity risk: If the stock falls below the conversion price, the bondholder won't convert. They are stuck with a low-coupon bond in a deteriorating company—the worst of both worlds.

Liquidity risk: Convertible bonds trade in smaller volumes than straight bonds. Bid-ask spreads are wider, making them hard to exit quickly.

Dilution risk: If the company converts the bonds (forces conversion by calling), existing shareholders are diluted. The bondholder becomes an equity holder in a larger capital base, reducing percentage ownership.

Forced conversion timing: If the issuer calls when the stock has just barely risen above the conversion price, the bondholder is forced to convert at a low equity value. The issuer times the call to minimize bondholder upside.

Real examples of convertible bonds

Tesla 0.25% Convertible Senior Notes due 2026 (issued 2014):

• Coupon: 0.25% (extremely low, issued in a low-rate environment)
• Conversion price: $359.87
• Tesla stock in 2014 was $150–200; the bond's premium was roughly 75–140%
• Tesla's stock soared to $600+; the bond was called in 2020, forcing conversion at $359.87
• Bondholders converted into $600+ of stock value, realizing substantial gains but missing the full upside beyond the call price

Microsoft convertible bond (historical example):

• Microsoft issued convertibles at lower rates than straight debt in the 1990s and early 2000s
• Conversion was accretive; most converted
• Shareholders were diluted, but Microsoft issued relatively few convertibles and had strong growth to offset dilution

Distressed company convertible:

• Retailer Company issues 5.0% convertible bonds when its straight debt would cost 10%+ (too risky)
• Bondholders accept 5.0% coupon for equity upside
• If Retailer's stock remains weak, bondholders collect 5% coupons with a bond floor
• If stock recovers, bondholders convert into equity at the conversion price

Convertible decision tree

Next

Some corporate bonds pay interest that resets periodically based on short-term interest rates (SOFR, prime rate). Floating-rate bonds protect against rising rate environments and appeal to investors hedging interest-rate risk.

Related concepts

• Callable Corporate Bonds
• Puttable Corporate Bonds
• What Corporate Bonds Are