When economists aggregate people’s wellbeing to make judgement about the overall good of a society, they sometimes discount later wellbeing compared with earlier wellbeing. This makes good sense only if all wellbeing is dated, which implies that wellbeing is separable across times. But this sort of separability makes it hard to take proper account of the value of extending people’s lives. Any solution to this problem will depend on a theory about the value of population. The upshot is that any theory of discounting is committed to a particular ethics of population.