The capital and liquidity provisions of Basel III are intended to shield the global financial system from a new financial crisis. Yet the extent to which they represent a good trade-off between financial stability and economic growth is still unclear. Policymakers still know little about the potential impact of Basel III on lending to SMEs, apart from the fact that it will be disproportionate. With the sector contributing half of the world's private-sector output, this uncertainty renders all existing impact assessments virtually irrelevant. In this discussion paper, ACCA considers how an impact assessment can be designed that would be 'about right' as opposed to very precisely wrong.