The buffer is intended to be useable in times of stress, and the regulatory consequences of falling into the buffer are accordingly less severe than the consequences of falling below the minimum. The surcharge on systemically important banks requires systemically important firms to recognize, and hold capital against, the costs that their failure would impose on the broader economy.
The minimum and buffer requirements were calibrated using historical data on bank losses across a number of countries in a way that would be appropriate for all large banks across a range of countries, although we recognized at the time that these requirements might not reflect market circumstances in all situations.