App-Based Couponing as a Customer Retention Instrument in Discount Grocery Retail: A Comparative Case Study of Lidl Plus and the Penny App

The German grocery retail sector is characterized by intense price competition and declining brand loyalty, prompting discounters to develop digital retention mechanisms beyond conventional promotions. This study investigates how app-based couponing supports customer retention in discount retail through a multiple case study design comparing the Lidl Plus and Penny apps. Drawing on couponing psychology, the Technology Acceptance Model, and gamification research, the two apps are evaluated across six criteria: couponing strategy, user-friendliness, perceived usefulness, pricing policy, gamification elements, and personalization. Data was gathered through a two-week active usage phase in January 2026. Findings indicate that both apps leverage coupons as psychological engagement tools, exploiting effects such as smart shopper feelings, fear of missing out, and the goal gradient effect. Key differences lie in timing and interaction design: Lidl Plus prioritizes immediate post-purchase rewards, while Penny emphasizes pre-visit planning. The study highlights that effective mobile retention in grocery retail requires a coherent combination of usability, personalization, and gamification.