What the buffer is
The capital conservation buffer is the standing, non-discretionary element of the combined buffer requirement. It obliges every credit institution to hold common equity tier 1 capital equal to 2.5% of its total risk exposure amount, on top of the Pillar 1 minimum and any Pillar 2 requirement. Unlike the other buffers, it does not vary with the credit cycle, an institution's systemic importance or the decisions of a macroprudential authority: it is the same 2.5% for all banks, phased in when the framework was introduced and now fully applicable.
Its purpose is to build a usable layer of capital in good times that can be drawn down in a downturn. Because the buffer sits above the minimum requirements rather than within them, a bank can absorb losses that eat into it without breaching its Pillar 1 or Pillar 2 requirement and therefore without immediately becoming non-viable. Using the buffer is expected; the framework simply attaches consequences to distributions while the buffer is depleted.
How it works in practice
The capital conservation buffer is one of the components that make up the combined buffer requirement, alongside the institution-specific countercyclical capital buffer, the systemic risk buffer and, for systemically important banks, the G-SII and O-SII buffers. All of these must be met with common equity tier 1 that is not also used to satisfy the minimum requirements or the Pillar 2 requirement.
If a bank's CET1 falls into the combined buffer, it becomes subject to the maximum distributable amount: dividends, additional tier 1 coupons and discretionary bonuses are automatically restricted according to how far into the buffer the shortfall reaches. This makes the buffer a graduated early-warning mechanism rather than a hard failure point. Because the buffers sit above the going-concern minima, they also sit above a bank's resolution-related requirements in economic terms, and the same CET1 cannot be counted twice towards both the combined buffer and MREL.
Legal basis
The capital conservation buffer is set out in the CRD, Article 129, which fixes it at 2.5% of the total risk exposure amount and requires it to be met with common equity tier 1. It forms part of the combined buffer requirement defined in Article 128, and its breach engages the maximum distributable amount mechanism in Article 141. The total risk exposure amount against which it is calculated is defined in the CRR, Article 92(3).
Practical relevance for banks and investors
For banks, the capital conservation buffer is the baseline cushion that management is expected to protect in ordinary conditions and to release, deliberately, under stress. For investors, and in particular holders of additional tier 1 instruments, the buffer matters because it is part of the CET1 stack whose depletion triggers distribution restrictions: a bank operating close to the top of its combined buffer has less headroom before coupons on AT1 can be curtailed. The buffer is therefore a key input into any assessment of distribution and coupon risk.