The paper evaluates the predictive validity of stated intentions for actual behaviour. In the context of the 2017 Dutch parliamentary election, we compare how well polls based on probabilistic and deterministic questions line up with subsequent votes. Our empirical strategy is built around a randomized experiment in a representative panel. Respondents were either asked which party they will vote for or were asked to allocate probabilities of voting for each party. The results show that probabilities predict individual behaviour better than deterministic statements for a large majority of respondents. There is, however, substantial heterogeneity in the predictive power of subjective probabilities. We find evidence that they work better for those with higher probability numeracy, even though probability numeracy was measured 8 years earlier.