The context in which decisions are learned can influence what choices we prefer in new situations. Such dependencies are well replicated and often lead to decision biases, i.e. choices that deviate from rational choice theory. We propose a simple computational model of such biases. To test the model, we analyzed behavioral data from 351 male and female participants in a series of nine value-based decision tasks and re-analyze six previously published datasets (n = 350 participants). Our results show that the combination of two basic principles, learning by reward, and repetition of decisions, is sufficient to explain biased preferences across all 15 datasets. Using standard analysis and hierarchical Bayesian model comparison we found that the proposed model provides a better explanation than previous accounts. In addition, our results show that higher choice frequency is linked to higher subjective valuation and lower value uncertainty. Results indicate that repetition is an important mechanism in shaping preferences.