A household’s purchase pattern for food can be described along three dimensions: how much food is bought, what types of food are bought, and how often food is bought. We have proposed a model in which these three facets of purchase behavior are simultaneously determined. Among other things, our model allows us to ask whether a household’s frequency of purchase influences how much food is bought on any shopping occasion. This was not possible with past studies. We find that, in fact, the more time has elapsed between purchases, the greater the quantity of product a household will buy on its next shopping occasion.