Maintenance of genetic diversity is critical for the preservation of small populations. Most captive populations are small and managers focus their efforts on reducing extinction risks by minimising loss of genetic diversity. To project changes in genetic diversity, managers use a genetic drift model. We used data from 40 managed captive populations to test whether this drift model is a good predictor of change in genetic diversity by comparing projected 10-year trajectories of annual loss in expected heterozygosity with the changes estimated from pedigree analysis. We found that the drift model frequently overestimated the rate at which genetic diversity would be lost and could not predict increases, which we observed in 22 species. We suggest that the drift model does not adequately reflect the potential for management strategies, such as prioritised breeding recommendations and recruitment of potential founders, to slow the loss of genetic diversity. In many cases, the drift model may be overly pessimistic, leading managers to seek solutions such as importation, increased population size or the abandonment of a captive population, that may be unnecessary or premature. Managers should be cautious when interpreting results from genetic drift models, taking care to assess how management actions might lead to more optimistic prognoses.