Seasonal influenza causes 20,000 hospitalizations and 36,000 deaths in the U.S. each year. Past psychology research has demonstrated that prompting people to form an implementation plan of the form, "When situation x arises, I will implement response y," increases attainment of desired goals because the desired behavior is linked to a concrete future moment. This type of planning prompt is a "nudge" in the direction of desired behavior that can be implemented at minimal expense and does not restrict individual autonomy. We conducted a 3-arm randomized controlled trial to test whether a low-cost planning intervention could increase influence vaccination rates. We show that planning prompts can be successfully applied to improve health behaviors.