There is a growing need in the marketing field to understand how consumers can be persuaded to consume healthier products. This research makes novel predictions about the time-of-day effects on (un)healthy product purchases based on self-control theory. We investigated whether and how time of day (morning vs. evening) influences consumers’ (un)healthy product purchases. A field study based on point-of-sales data indicated that consumers tend to buy more unhealthy products in the evening. Two laboratory experiments confirmed that this is due to a decrease in self-control in the evening, which leads consumers to purchase more unhealthy products at this time. A follow-up eye-tracking experiment further revealed potential mechanisms whereby lower self-control causes consumers to focus more on unhealthy products and weakens the effect of attention to healthy products on purchases. The findings provide valuable insights into consumer behavior and marketing decisions for marketing academics, retailers and consumer marketing companies.