Introduction
Vanilla convertible bonds give the holder the right (but not the obligation) to convert into stock; if the stock never reaches the conversion price, the bonds redeem at par at maturity and there is no dilution. Mandatory convertibles invert that economics: they automatically convert into common stock at maturity regardless of the stock price, with the conversion ratio scaled to deliver the par value of the original investment. The structure trades the bond-floor protection of vanilla convertibles for a higher dividend, more accounting and rating-agency flexibility, and (on the issuer's side) certainty of eventual equity issuance. Convertible preferred stock applies similar logic in a perpetual or long-dated preferred-equity wrapper rather than a debt wrapper, paying preferred dividends rather than bond coupons. Both structures occupy a distinct part of the equity-linked product set, and the 2024-2025 cycle has produced a notable resurgence in mandatory and convertible-preferred issuance, particularly among crypto-treasury issuers like Strategy (formerly MicroStrategy) that have raised tens of billions of dollars through a series of perpetual preferred structures. A bank pitching a rating-sensitive industrial or a crypto-treasury company has to know which wrapper unlocks how much equity credit and what dividend cost the issuer will pay for it.
Mandatory Convertibles
Mandatory convertibles are debt-style securities that automatically convert into common stock at maturity, eliminating the investor's option to receive cash redemption.
The Forced-Conversion Mechanic
A mandatory convertible matures at a defined date (typically 3 years) and converts into common shares regardless of stock price. The conversion ratio scales with the stock: investors receive more shares if the stock has fallen and fewer if it has risen, subject to upper and lower share-count caps. Investors do not receive cash at maturity (unlike vanilla converts) and bear full equity downside below the structure's lower threshold.
- Mandatory Convertible
A hybrid security that automatically converts into common stock at a defined maturity date (typically 3 years), regardless of the stock's price at maturity. Mandatory convertibles trade the bond-floor protection of vanilla convertibles for a higher dividend (typically 4-6 percent) and more favorable rating-agency equity-credit treatment. The two principal structures are PERCS (capped upside) and DECS (dual-strike design with payoff flat at par between strikes and geared upside above the upper strike). Issuers use mandatory convertibles primarily when they need balance-sheet capital but want to preserve their credit rating, which the equity-credit treatment supports.
PERCS
Preferred Equity Redemption Cumulative Stock (PERCS) is a mandatory convertible that pays a higher dividend than common stock (100 to 300 bps higher) and converts into a fixed number of common shares at maturity with a cap on investor upside. The PERCS payoff at maturity is:
PERCS were popular in the 1990s for issuers to deliver forward-equity at a premium while paying a coupon-like dividend.
DECS
Dividend Enhanced Convertible Stock (DECS) is the more flexible mandatory structure: at maturity, the conversion ratio scales with the stock price across a defined range with a "lower strike" that anchors the issuance economics and an "upper strike" that caps the investor's upside. The classic DECS payoff at maturity is piecewise:
DECS is the dominant modern mandatory structure because the dual-strike design is more attractive to investors than the single-cap PERCS structure: full downside exposure if stock falls below the lower strike, payoff flat at par between the strikes, partial (geared) upside above the upper strike.
The Broader Mandatory Family (PRIDES, ACES, STRYPES)
The mandatory product family extends beyond PERCS and DECS to include similar structures named by the issuing bank's marketing team: PRIDES (Merrill Lynch), ACES (Goldman Sachs), STRYPES. Historical issuers have included Texas Instruments, General Motors, Citicorp, American Express, and Boise Cascade, with peak issuance in the late 1990s and early 2000s.
Bayer and Boston Scientific Examples
Bayer's €4 billion mandatory in late 2016 funded part of its $66 billion Monsanto acquisition, capturing equity-credit treatment that preserved its investment-grade rating through a transformative deal. Boston Scientific issued approximately $880 million of 5.5 percent mandatory convertible preferred in 2020 (8.8 million shares at $100 liquidation preference), paying dividends through 2023 when Boston Scientific called for mandatory conversion at the typical 3-year lifecycle conclusion.
The Rating-Agency Equity Credit Rationale
Issuers use mandatory convertibles primarily to capture the rating-agency equity-credit benefit. Rating agencies (S&P, Moody's, Fitch) treat mandatory convertibles as 50 to 100 percent equity for credit-rating purposes, lowering effective leverage versus a debt issuance. The treatment is more favorable than vanilla convertibles (mostly debt) and is the principal rationale for choosing the mandatory format. Capital-heavy issuers (utilities, industrials, banks) use mandatories when they need balance-sheet capital but want to preserve credit ratings.
- Equity Credit (Rating Agency)
The treatment that S&P, Moody's, and Fitch give to hybrid securities (mandatory convertibles, convertible preferred, perpetual preferred) for credit-rating purposes. Equity credit ranges from 0 percent (treated as pure debt) to 100 percent (treated as pure equity), with most hybrid structures receiving 50 to 100 percent depending on specific structural features (perpetuity, dividend deferral rights, lack of step-up). Higher equity credit lowers the issuer's effective leverage from a rating-agency perspective, which can support credit ratings or unlock additional debt capacity. Equity credit is one of the principal structural inputs the rating agencies use to differentiate hybrid securities from straight debt.
The equity-credit benefit is not free: the issuer pays for it through a meaningfully higher dividend than a vanilla convertible would carry, and accepts certain equity issuance at maturity rather than the optional conversion of a vanilla bond. That trade-off is the central economic decision the issuer is making when picking the mandatory format.
DECS Payoff Worked Example
A representative DECS structure: an issuer trading at $100 issues a 3-year DECS with a $100 lower strike and $120 upper strike, paying a 5.5 percent dividend. At maturity: if stock is at $80, investors receive shares worth $80 (full downside below lower strike); if stock is at $110, investors receive shares worth $100 (payoff flat at par between the strikes); if stock is at $140, investors receive shares worth approximately $116.67 (geared partial upside, calculated as $100/$120 times $140). The structure delivers the issuer's desired forward-equity issuance at a price between the lower and upper strikes, with the dividend payments compensating investors for the capped upside in the meantime.
Convertible Preferred Stock
Convertible preferred stock is preferred equity that is convertible into common stock under defined terms, distinct from mandatory convertibles in the wrapper (preferred equity vs debt) and the absence of a fixed maturity.
The Preferred Equity Wrapper
Convertible preferred is structurally preferred stock: a class of equity with priority over common stock in dividends and liquidation, paying a fixed preferred dividend rather than a bond coupon. Most convertible preferred is perpetual (no maturity) or has a long-dated mandatory conversion (10+ years out), and the structure pays preferred dividends throughout its life until conversion or redemption.
Cumulative vs Non-Cumulative; Convertibility
Dividends are structured as cumulative (skipped dividends accrue and must be paid before common dividends resume) or non-cumulative (skipped dividends forfeited). Cumulative structures price at tighter yields; non-cumulative at higher yields. Strategy's STRC perpetual preferred uses a cumulative structure with a compounding rate increase for unpaid dividends, escalating from a starting yield up to 18 percent per annum if the issuer skips multiple payments. Convertible preferred can be converted at the holder's option at a defined conversion price or with automatic conversion at a defined common-stock level.
The Strategy 2025 Suite
Strategy (formerly MicroStrategy) issued a series of perpetual preferred structures throughout 2025 to fund Bitcoin treasury accumulation: STRK (Strike, 8 percent fixed dividend, convertible), STRF (Strife, 10 percent cumulative non-convertible), STRD (Stride, 10 percent non-cumulative non-convertible), and STRC (Stretch, variable cumulative with compounding mechanic). The suite has cumulatively raised tens of billions and represents the most distinctive 2025 capital-markets episode, with each structure capturing a different point on the rate-protection vs equity-upside continuum.
How Mandatory and Convertible Preferred Compare
A vanilla convertible, a mandatory, and a convertible preferred sit at three different points along the debt-to-equity continuum, with progressively higher dividends and progressively more equity credit at each step.
| Dimension | Vanilla Convertible | Mandatory Convertible | Convertible Preferred |
|---|---|---|---|
| Wrapper | Senior debt | Senior debt or preferred | Preferred equity |
| Maturity | 5-7 years (cash redemption option) | 3 years (forced conversion) | Perpetual or 10+ years |
| Coupon/dividend | 1-3% | 4-6% | 6-10%+ |
| Bond floor | Yes (PV of coupon + par) | None (forced conversion) | Limited (preferred priority) |
| Rating-agency treatment | Mostly debt | 50-100% equity credit | 100% equity credit |
| Best fit | Growth issuers, refis | Rating-sensitive capital-heavy issuers | Crypto treasury, perpetual structures |
When Each Structure Wins
Mandatory convertibles win when the issuer prioritizes rating-agency equity credit and is comfortable with certain eventual equity issuance (capital-heavy issuers with leverage near rating thresholds). Convertible preferred wins when the issuer wants permanent or near-permanent equity-credit capital without debt maturity pressure and is willing to pay a higher dividend, working well for structural balance-sheet capital and the dominant tool for crypto-treasury companies in 2025 where the perpetual nature aligns with indefinite holding strategy.
The STRC mechanic only works because the rating agencies have already blessed the perpetual structure as 100 percent equity credit. Without that classification, the same instrument would count as debt for leverage purposes and the entire balance-sheet logic would collapse. That is why every hybrid issuance starts with a rating-agency criteria conversation rather than a marketing one.
PERCS, DECS, perpetual preferred: variations on the same idea, forced or quasi-forced equity issuance through a hybrid wrapper that earns rating-agency equity credit. Every structure covered so far converts into the issuer's own stock; a different structure entirely lets a parent company monetize a holding in a separately-listed subsidiary by issuing a bond that converts into the subsidiary's shares rather than the parent's. Exchangeable bonds are next.
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