Current approaches to valuing biodiversity and ecosystem damage rest largely on standing stock or on contingent monetary estimates, neither of which captures the cumulative ecological work an organism performs over its life. Using Dynamic Energy Budget theory and curated parameter sets for the whole Add-my-Pet collection, we reconstructed the complete carbon life history of more than seven thousand animal species, from fertilisation to death, and defined a dimensionless index — the carbon functional debt — as the ratio of total lifetime carbon ingestion to instantaneous standing carbon. The index counts how many times over an organism reprocesses its own standing carbon during life. Three regularities emerge. First, it is essentially invariant with body mass across fourteen orders of magnitude, holding within and across taxa, because lifetime ingestion and standing carbon scale almost identically with size so that their ratio is mass-free. Second, the carbon an organism would still process if it completed its expected life dominates the early life course, crossing the carbon already processed only past the midpoint of life; the functional cost of losing a young individual therefore far exceeds its standing biomass, giving a mechanistic basis for the disproportionate weight of recruitment and juvenile survival. Third, the index is sharply tiered by thermal strategy, endotherms carrying an order-of-magnitude higher debt than ectotherms, whose values match independent estimates from production-to-biomass ratios. We discuss how this individual-level currency can be aggregated from individuals to populations and communities, and applied to conservation, restoration and impact assessment as a common, mechanistic and monetary-independent measure of ecological function gained or lost.