In Copenhagen in 2009, developed countries committed to jointly mobilise $100 billion dollars a year by 2020 to address the needs of developing countries. However, the climate accords rely on pledging and do not include any formulae for determining how responsibility for this target should be apportioned among developed countries. This paper suggests three metrics to assess each developed country’s fair share of the climate finance goal: gross national income, cumulative carbon dioxide emissions and population. While imperfect, these metrics offer an indicative range to begin holding individual national governments to account.