Mobilizing climate finance for developing countries is crucial for achieving a fair and effective global climate regime. To date developed countries retain wide discretion over their national contributions. We explore how different degrees of international coordination may influence the fairness of the global financing effort. We present quantitative scenarios for (i) the metrics used to distribute the collective effort among countries contributing funding; and (ii) the number of contributing countries. We find that an intermediate degree of coordination—combining nationally determined financing pledges with a robust international review mechanism—may reduce distortions in relative efforts as well as shortfalls in overall funding, while reflecting reasonable differences over what constitutes a fair share. Broadening the group of contributors may do little to improve adequacy or equity unless the more heterogeneous group can converge on credible measures of responsibility and capacity. The analysis highlights the importance of building common understandings about effort-sharing.