Lockdown measures in response to the COVID-19 pandemic involve placing huge burdens on some members of society for the sake of benefiting other members of society. How should we decide when these policies are permissible? Many writers propose we should address this question using cost-benefit analysis, a broadly consequentialist approach. We argue for an alternative non-consequentialist approach, grounded in contractualist moral theorising. The first section sets up key issues in the ethics of lockdown, and sketches the apparent appeal of addressing these problems in a CBA frame. The second section argues that CBA fundamentally distorts the normative landscape in two ways: first, in principle, it allows very many morally trivial preferences—say, for a coffee—might outweigh morally weighty life-and-death concerns; second, it is insensitive to the core moral distinction between victims and vectors of disease. The third section sketches our non-consequentialist alternative, grounded in Thomas Scanlon’s contractualist moral theory. On this account, the ethics of self-defence implies a strong default presumption in favour of a highly restrictive, universal lockdown policy: we then ask whether there are alternatives to such a policy which are justifiable to all affected parties, paying particular attention to the complaints of those most burdened by policy. In the fourth section, we defend our contractualist approach against the charge that it is impractical or counterintuitive, noting that actual CBAs face similar, or worse, challenges.