In recent years, scandals involving improper use of financial resources by parliamentarians have led to the establishment of new independent regulatory agencies. Two such agencies are the UK’s Independent Parliamentary Standards Authority (IPSA), set up after the 2009 expenses scandal, and Australia’s Independent Parliamentary Expenses Authority (IPEA), established in 2017. Because of their unique relationship with legislative bodies, commentary on these regulators has focused on the level of independence attained by the regulatory agency from the parliamentary principle, itself the regulated actor. At the same time, little attention has been paid to other important differences in their accountability structures which affect policy making. This paper leverages the Calibrated Public Accountability (CPA) model (Schillemans, 2016) to explain important differences between IPSA and IPEA. Using a legal analysis coupled with an extensive document review, the paper demonstrates that IPSA is an example of a regulator accountable for process (producing well-considered decisions) while IPEA is accountable for outcomes (producing accurate decisions). This variance can be explained by the different nature of the reputational damage sustained during scandals by the pre-reform systems in the UK and Australia, which was both more extensive and more unexpected in the former case. In addition to demonstrating the utility of the CPA model for small-n comparative studies, therefore, the analysis demonstrates that the proliferation of independent parliamentary finance regulators is not simply due to institutional isomorphism. Instead, choices about regulatory accountability are conditioned by policymakers assessments of how best to prevent particular forms of reputational damage from recurring in the future.