AT1 — Additional Tier 1 Capital

AT1 (Additional Tier 1) is the second tier in the Basel III capital framework. A bank's capital structure stacks from top to bottom: CET1 (Common Equity Tier 1) → AT1 → Tier 2 → Senior debt. When losses occur, they are absorbed from the top — shareholders (CET1) go first.

AT1 trades in bond markets like a bond. It has a coupon, a CUSIP or ISIN, and a Bloomberg quote. But legally it is capital — it has no maturity (perpetual structure), coupon payments are discretionary rather than obligatory, and it automatically absorbs losses if the bank's capital ratio falls below a specified trigger. This dual nature — looking like a bond but functioning as capital — is what makes AT1 complex and easy for investors to misunderstand.

Why do banks issue AT1? The primary driver is cost efficiency. Issuing common equity (CET1) dilutes existing shareholders. AT1 allows banks to meet regulatory capital requirements without diluting equity, in exchange for paying investors a higher coupon. From the issuer's perspective, it is the optimal instrument for simultaneously managing capital ratios and protecting shareholder value. The global AT1 market had grown to approximately $250 billion or more by 2024, with major European and Asian banks as the dominant issuers. The instrument became a cornerstone of post-crisis bank capital structures precisely because it accomplishes what regulators want — genuine loss absorption — while giving issuers a capital-efficient tool that sits comfortably within institutional fixed income portfolios.

AT1's structure is defined by three core features: the coupon, the call option, and the loss-absorption trigger.

First, the coupon is discretionary. On a conventional bond, missing a coupon constitutes a default. AT1 works differently. The regulator may prohibit coupon payments, or the issuer itself may cancel them at its discretion. When a bank's Maximum Distributable Amount (MDA) becomes insufficient, coupon payments can be automatically restricted. This discretionary non-payment risk is a principal driver of the spread premium investors demand on AT1 instruments.

Second, there is a call option. AT1 is perpetual in legal structure, but issuances typically set a First Call Date five or ten years after issuance. The issuer has the right — not the obligation — to redeem the bonds at par on that date. Market convention treats a First Call Date as an implied redemption commitment; if the issuer skips the call and extends the bond, it sends a strongly negative signal to the market, typically causing the issuer's AT1 spreads to widen significantly. The option remains the issuer's right, not the investor's.

Third — and most critically — is the loss-absorption trigger. AT1 carries two distinct loss-absorption mechanisms. The first is a mechanical trigger: if the CET1 ratio falls below 5.125% (or whatever level is specified in the prospectus), the AT1 automatically converts to equity or its principal is written down. The second is the PONV (Point of Non-Viability) trigger: if the regulator determines the bank is no longer viable, mandatory loss absorption is imposed by regulatory action. The Credit Suisse episode of March 2023 is the definitive real-world example of the latter — CHF 16 billion of AT1 was written to zero under FINMA's PONV declaration, even as shareholders retained some residual value.

Investors buy AT1 for one straightforward reason: yield. AT1 coupons typically run 200–400 basis points or more above the same issuer's senior bonds. In exchange for accepting a structurally subordinated position, investors receive a meaningful additional return. This spread premium is compensation for the three risks described above — discretionary coupon cancellation, call skip, and loss absorption under trigger events.

But the reasons for caution are equally clear. The central concern is the asymmetric risk embedded in PONV provisions. The prospectus states that if the regulator declares a PONV, the entire principal can be written to zero. The problem is that a PONV declaration typically occurs precisely when the bank is receiving emergency support or being forced into a merger — a moment when shareholders may still retain residual value even as AT1 holders face total loss. The Credit Suisse episode of March 2023 was exactly this scenario: equity holders received merger consideration while CHF 16 billion of AT1 was written to zero.

The second risk is jurisdictional. PONV mechanics vary materially across countries. Swiss law and FINMA's mandate explicitly permit AT1 write-down ahead of equity — a provision that was clearly disclosed in Credit Suisse's prospectus but underweighted by many buyers. The EU and UK generally follow a principle of equity absorbing losses first before AT1. Investors must verify which jurisdiction's laws govern the issuance and exactly what the prospectus says about loss absorption sequencing. The investors most shocked by the CS outcome were those who bought on yield and brand name without parsing the legal terms. AT1 is a product that demands detailed prospectus analysis before any position is taken.