Reforestation and restoration offer critical contributions to addressing climate change and biodiversity decline. Enabling carbon credits to be derived from these activities is important for reforestation, particularly since reforestation does not come cheaply. Australia's Carbon Farming Initiative is a world-leading policy that allows carbon credits to be obtained by using published methods-based approaches. Here we apply two different approaches to a young mixed species reforestation project in the wet tropics of Queensland, Australia. One approach assesses carbon sequestration from published allometric equations requiring direct field measurements, and the other applies a national carbon accounting model, FullCAM. Using allometric equations, we found above-ground biomass was influenced significantly by family, species, size class, and the interaction of family and size class. Species in the family Proteaceae out-performed species in other families. Selection of species according to soil nutrient status could enhance growth rates, but if soil nutrients and species responses are not known, then a bet-hedging strategy using mixed species from a variety of families is probably the best option. For three year old forest plots, FullCAM modelled significantly more carbon mass of trees than published allometric models for mixed tropical forests, suggesting that FullCAM needs adjustment to more accurately reflect species, families, local conditions and small-scale sites. Current policy settings are at odds with the needs of carbon farmers, considering the importance of forests and landscape restoration in fighting climate change and biodiversity decline. Legislated national methods allowing the development of species-specific allometrics for small mixed plantations do not account for the costs of developing these allometrics, especially in markets that are marginal.