Corporations, governments, and even people on the street routinely weigh the benefits and costs of their decisions, so why don’t philanthropists? By estimating the social return on their investments, funders can deploy their dollars more effectively. To demonstrate the power of these calculations, the authors show how three organizations – the Robin Hood Foundation, Acumen Fund, and the William and Flora Hewlett Foundation – use cost-benefit analysis to evaluate their ongoing programs, choose mission investments, and plan long-term strategies.