It is estimated that the global yearly expenditure on biodiversity conservation action exceeds one billion U.S. dollars. One of the key tools for prioritizing conservation actions is the International Union for Conservation of Nature (IUCN) Red List, the most authoritative and comprehensive source of information on the global extinction risk of species (covering ca. 60,000 as of today). While IUCN's vision is to increase the taxonomic coverage of the Red List, no adequate plan exists to keep it up to date. As species assessments become outdated after 10 years under IUCN rules, our simulations reveal that with the limited budget currently available for reassessment, most of the Red Listing effort may be wasted soon. Indeed, 17% of the species’ assessments are already outdated. To minimize the budget needed to keep assessments up to date in the Red List, we propose a mixed strategy of online reassessments and budget growth. We show that largely replacing workshops with online consultations is a more sustainable strategy that would save U.S. $2.8 million per year (35% of the budget). Sharing the cost of such a strategy among Organization for Economic Co-operation and Development (OECD) countries (U.S. $156,000 per country per year) would ensure that the multimillion dollar spending based on the Red List remains effective in the long term.