While many expect happiness to decline in old age, research into well-being and happiness suggests otherwise. Happiness is U-curved, with the bottom of the U, the unhappiest part, experienced in middle age, and happiness increasing thereafter. This surprising diachronic phenomenon presents ethical questions concerning the way we perceive our own and other people's lives, and how individuals and society ought to respond to ageing. I claim the U-curve could influence, inter alia, our attitudes to our own ageing, debates concerning prioritisation of the elderly in health decisions, and attitudes towards end-of-life decisions. As an example of how the U-curve can influence the conclusion of an applied ethical problem in population ethics, I revisit Peter Singer’s claim that substantially extending later life would reduce total utility. With some qualifications, I defend Mark Walker’s claim that, in undermining the crucial empirical assumption that life gets worse as we age, the U-curve casts doubt on Singer’s critique of life extension.