A debenture is a debt instrument, but its name alone does not tell you whether assets secure it, where it ranks in a default, or whether it can turn into shares. Read those terms before focusing on the coupon.
The jurisdiction changes what the word suggests
In U.S. corporate-bond usage, debentures commonly mean unsecured debt: no specified collateral backs the obligation. “Unsecured” does not mean every creditor has equal priority. Senior and subordinated obligations can have different claims. The SEC's bond introduction explains corporate debt, security, and ranking.
In the UK, a company debenture can be secured, including by fixed or floating charges. The Insolvency Service's creditors-and-liabilities guidance, section 43.127, uses the term more broadly. Do not translate a U.S. definition into a conclusion about a UK document.
Security identifies assets supporting a claim; seniority concerns the claim's position relative to others. Neither guarantees full recovery. Collateral can be worth less than expected, and insolvency outcomes depend on the governing law, issuer structure, documents, and available assets.
Read the repayment promise as a set of conditions
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| Term | Meaning | Question to resolve |
|---|---|---|
| Principal and maturity | The amount owed and scheduled repayment date. | Is principal paid at maturity, in installments, or under another mechanism? |
| Coupon | The contractual interest payment rule. | Fixed or floating, paid how often, and may payment be deferred? |
| Security and ranking | Collateral and the claim's priority. | Which entity owes the debt, and what obligations rank ahead? |
| Call or redemption | Rights to repay before the scheduled end. | Who can trigger repayment, when, and at what price? |
| Conversion | A mechanism linking the debt to equity. | Who controls conversion, how is the share number calculated, and is settlement in shares, cash, or a combination? |
| Covenants and default | Issuer promises and consequences of specified breaches. | What protections, exceptions, remedies, and consent thresholds apply? |
Coupon is not yield
A $1,000 face-value instrument with a 5% annual coupon pays $50 a year under that simple rule. If purchased for $950, its current yield is $50 ÷ $950 = about 5.26%. Current yield ignores the difference between purchase price and eventual repayment, along with the timing of those cash flows.
Yield to maturity incorporates the scheduled cash flows and purchase price under assumptions about holding and payment. A callable issue also needs examination of earlier-redemption outcomes. FINRA's guide to bond yield and return distinguishes these measures. None is a promise that the issuer will pay or that an early sale will recover the purchase price.
For conventional fixed-rate bonds, market prices generally fall when required yields rise, with sensitivity affected by duration and other features. Credit concerns can move prices even when benchmark rates do not change. FINRA explains duration and interest-rate risk. The mortgage-rate guide shows why a Fed announcement and an individual borrowing rate are also different things.
A fictional convertible debenture
Invented teaching terms, not an offering or a legal template: principal is $1,000, maturity is five years, and the annual coupon is 5%, paid at each year-end. Assume senior unsecured debt with no issuer call. After a scheduled coupon is paid, the holder may choose to convert into 40 newly issued shares. If the holder does not convert, principal is due at maturity. All scheduled payments assume no default.
These terms deliberately omit the complexity of a real indenture. The downloadable fictional term sheet and calculations (text) records the assumptions so the example can be checked or discussed.
If it remains debt
The holder receives $50 at each of five year-ends and $1,000 principal at the fifth year-end. That is $250 in coupons plus $1,000 principal, or $1,250 total scheduled cash, without discounting. Principal repayment is a return of lent capital, not an additional $1,000 investment profit.
If it converts
The conversion ratio implies $1,000 ÷ 40 = $25 of principal per share. At a hypothetical share price of $20, the 40 shares have a conversion value of $800; at $30, they have a value of $1,200. These are share values at that moment, excluding the coupon just paid. In this example, conversion ends the debt claim and future coupons.
The comparison is not simply “convert whenever shares exceed $1,000.” The debt itself has a market value, and remaining coupons, option value, issuer risk, restrictions, and taxes can matter. Real conversion terms may use different triggers, adjustment clauses, or settlement methods. The SEC's convertible-securities explanation describes the debt-to-equity relationship and dilution concerns.
What issuing the shares does to ownership percentages
Suppose the fictional company has 1,000,000 shares outstanding and 1,000 identical debentures. If all convert at 40 shares each, it issues 40,000 shares and has 1,040,000 in total. An existing owner who retains 10,000 shares moves from 1% ownership to about 0.9615%. The percentage shrinks, but this arithmetic alone cannot predict the share price or the economic value of the company after its debt is extinguished.
Use the actual documents to finish the analysis
Find the prospectus or offering document, the governing debt agreement, and current issuer financial information. Confirm the legal issuer, currency, denomination, maturity, ranking, collateral if any, and every early-redemption or conversion condition. Marketing summaries can omit exceptions that change the result.
Then ask how you would exit before maturity, what price information is available, and which costs apply. A stated maturity date does not create a liquid market. Compare the instrument with alternatives using the same time horizon and risk questions, rather than ranking coupons alone.
If an adviser or managed service holds the debt for you, ask how it fits the mandate and whether the service fee is separate from the investment's costs. The managed-account guide explains that second layer of decisions.