Behavioural forms of regulation, e.g. nudging and debiasing , increasingly take centre stage in regulatory agendas and are making their way into EU consumer law. In order to warrant for an effective implementation, findings from behavioural sciences need to conform with the regulatory context conditions of the underlying legal system and need to be fit for purpose to answer questions the law asks. Behavioural studies hence need to pass a regulatory validity test before they can be operationalised in the law. I will explain how such a regulatory validity test can work in EU consumer law. I will first illustrate the different context conditions of behavioural sciences on the one hand and of law on the other (I.). Subsequently, I will illustrate these differences on the example of a comparison of the recently commissioned behavioural science study by the European Commission on the “vulnerable consumer” and the legal requirements of the “average consumer” benchmark (II.). To overcome the shortfalls this example illustrates, I will introduce a regulatory validity test which can be applied by behavioural and legal scientist, courts, and regulators (III.). I will then conclude the findings (IV.).