An AT1 bond, short for Additional Tier 1 bond, is a perpetual, deeply subordinated bond issued by a bank to satisfy regulatory capital requirements. It pays a high coupon, has no maturity date, and can have its principal written down or converted into shares if the bank’s capital deteriorates or regulators judge the bank non-viable. AT1 holders sit just above common shareholders in the loss-taking order, which is why the yields are large and the risk of a total loss is real.
The instrument was created by the Basel III reforms after the 2008 crisis to make sure private investors, not taxpayers, absorb bank losses. Within Tier 1 capital, Common Equity Tier 1 (CET1) is the top layer, made up of common stock and retained earnings; AT1 is the layer below it, filled mainly by AT1 bonds and classified as “going concern” capital because it can absorb losses while the bank keeps operating.1Bank for International Settlements. Definition of Capital in Basel III AT1 must take losses before Tier 2 and senior creditors are touched. That pecking order is the whole point of the design.2Suara SEACEN. Loss Absorbency of Additional Tier 1 Capital Instruments under Basel III: The Credit Suisse Case
How AT1 Bonds Actually Work
Perpetual, With a Call Option
AT1 bonds have no maturity date. Only perpetual instruments qualify as Tier 1 capital under Basel III; anything with a fixed maturity can be Tier 2 at best.1Bank for International Settlements. Definition of Capital in Basel III
In practice, almost every AT1 bond includes a call option that lets the issuing bank redeem it at par, usually after five or ten years. Basel III requires a minimum of five years before the first call date and bans coupon step-ups or other features that would push the bank to redeem. The call is not automatic. The bank must obtain regulatory approval first, generally granted only if the called bond is replaced with capital of equal or better quality, or the bank’s capital position stays comfortably above its minimums.3Bank for International Settlements. Basel III Definition of Capital – Frequently Asked Questions European supervisors have told banks not to announce a call before that approval is in hand.4European Banking Authority. Continuous Call Option in AT1 Instruments
If the bank does not call, the bond keeps running and the coupon resets, typically to a fixed credit spread set at issuance plus a current benchmark swap rate. Because step-ups are prohibited, the new coupon can be lower than the original. This is extension risk, and when it lands the bond’s market price usually drops sharply.
Discretionary, Non-Cumulative Coupons
AT1 coupons do not behave like ordinary bond interest. The bank can cancel any scheduled payment at any time, for any reason, and skipping a coupon is not a default. The payments are also non-cumulative: a canceled coupon is gone, and the bank owes nothing for it later.5Bank for International Settlements. Basel III: A Global Regulatory Framework for More Resilient Banks and Banking Systems
Cancellation is most likely when the bank’s CET1 ratio falls into the capital conservation buffer zone above the regulatory minimum, where Basel III restricts dividends, buybacks, and discretionary bonus payments.6Bank for International Settlements. RBC30 – Buffers Above the Regulatory Minimum But the contractual terms let the bank cancel even without a regulatory push. Permanent, no-make-up loss of income is one of the features that pushes AT1 closer to equity than to debt.
How Losses Get Imposed
The defining feature of an AT1 bond is that the principal itself is at risk. Loss absorption is mandatory once triggered and does not depend on the bank’s willingness.
The CET1 Trigger
Every AT1 bond has a contractual trigger tied to the issuing bank’s CET1 ratio. Basel sets the floor at 5.125% of risk-weighted assets for instruments classified as liabilities.7Bank for International Settlements. FSI Briefs No 21 – Upside Down: When AT1 Instruments Absorb Losses Before Equity Some jurisdictions and issuers set it higher; the Bank of England uses 7%, and many European banks issue at that level voluntarily.8The Banker. How AT1 Bonds Have Made a Comeback
Once the CET1 ratio breaches the trigger, one of two things happens, fixed at issuance:
- Principal write-down. The face value is reduced, in part or in full. A full write-down wipes out the investor’s principal entirely. In some jurisdictions the write-down can be temporary, with a possible write-back if the bank returns to profitability; in others it is permanent.7Bank for International Settlements. FSI Briefs No 21 – Upside Down: When AT1 Instruments Absorb Losses Before Equity
- Conversion to equity. The bond is exchanged for common shares at a pre-set ratio. Because the conversion happens when the bank is in trouble, those shares are usually worth much less than the bond’s face value.
The Non-Viability Trigger
Regulators keep a separate power to impose losses on AT1 holders when they judge the bank has reached or is approaching the point of non-viability. The Basel framework defines that as the earlier of two moments: the authority deciding a write-down is needed to restore viability, or a decision to inject public support to keep the bank alive.7Bank for International Settlements. FSI Briefs No 21 – Upside Down: When AT1 Instruments Absorb Losses Before Equity
This trigger can fire even if the contractual CET1 trigger has not been breached. Regulators can override the bond’s terms and impose a full write-down or forced conversion, ensuring private capital is wiped out before public money is put on the line.
What the Credit Suisse Write-Down Showed
In March 2023, Swiss regulator FINMA ordered the complete write-down of roughly CHF 16 billion in Credit Suisse AT1 bonds as part of the emergency takeover by UBS.9IISD. Switzerland Faces ISDS Claims Over Credit Suisse AT1 Bond Write-Off The legal basis was a Federal Council emergency ordinance that gave FINMA the authority to order it.10Finadium. FINMA to Appeal Swiss Court Ruling That CS AT1 Write-Downs Lacked Legal Basis
The controversy was that Credit Suisse equity holders received something through the UBS share exchange while AT1 holders received nothing. In the normal creditor hierarchy, equity is wiped out before subordinated debt. The Swiss approach inverted that order, and European regulators quickly reaffirmed that in their jurisdictions equity would absorb losses before AT1, distancing themselves from the Swiss precedent.
The episode is the clearest case study of the risk. Write-down risk is not theoretical. Regulatory discretion can override the creditor order the market expects. And the legal framework governing these bonds varies from country to country in ways that matter.
Yields and What Drives Them
AT1 bonds sit in the high-yield corner of fixed income. The elevated coupons compensate investors for four distinct risks stacked on top of each other: subordination, perpetual duration, discretionary coupons, and the possibility of a total principal loss. The metric most quoted in the market is yield-to-call, which assumes the bank redeems the bond at the first opportunity.
Spreads move with the perceived probability of each of those risks materializing. A bank whose CET1 ratio sits comfortably above its buffer trades at tighter spreads; one drifting toward buffer constraints trades meaningfully wider, because coupon cancellation becomes more plausible. Extension risk shows up as a price drop when the market starts pricing in a missed call. Regulatory risk is the hardest to model because it depends on policy decisions rather than financial ratios, and, as the Credit Suisse case showed, emergency powers can go beyond what a bond prospectus contemplated.
After the initial Credit Suisse shock, European AT1 spreads tightened back toward pre-crisis levels, and by early 2026 they had compressed further. Demand recovered fast: UBS issued $3.5 billion of AT1 bonds in November 2023 that drew more than $36 billion in orders, suggesting institutional investors treated the Swiss write-down as a jurisdictional event rather than a flaw in the instrument itself.
Who Can Actually Buy AT1 Bonds
In the United States, AT1 bonds are typically sold as private placements under SEC Rule 144A. They are not registered with the SEC and are not available to the general public. Buyers must qualify as “qualified institutional buyers,” which generally requires owning and investing on a discretionary basis at least $100 million in securities of unaffiliated issuers; registered broker-dealers face a lower $10 million threshold.11eCFR. 17 CFR 230.144A – Private Resales of Securities to Institutions
Even where retail access is technically possible, the combination of perpetual duration, discretionary coupons, and possible total write-down makes these instruments unsuitable for most individual investors. The typical AT1 holder is an asset manager, insurance company, pension fund, or hedge fund with a dedicated bank-capital desk and the analytical machinery to model regulatory capital scenarios.