This study investigates the interplay between achievement emotions, user experience, and academic performance of online university assignments. Drawing on Pekrun’s Control-Value Theory (CVT), User Experience Theory (UXT), Self-Determination Theory (SDT), Cognitive Load Theory (CLT), and Expectancy-Value Theory (EVT), the research explores how these factors impact first-year students’ engagement and performance in a computer programming module. The sample comprised 350 responses across three assignments, with 292 responses for Assignment 1, 30 for Assignment 2, and 27 for Assignment 3. Achievement emotions were assessed using the Achievement Emotions Questionnaire (AEQ) across eight scales: enjoyment, hope, pride, anger, anxiety, shame, hopelessness, and boredom. The User Experience Questionnaire (UX) evaluated user experience across four scales: ease of use, interest, alignment, and appeal. Additionally, academic performance was measured as a percentage. Descriptive statistics revealed the prevalence of both positive and negative emotions, as well as varied user experiences. Correlation analysis indicated significant relationships between positive emotions (enjoyment, hope, pride) and higher academic performance, while negative emotions (anger, anxiety, hopelessness) were negatively correlated with performance. Positive user experiences (ease of use, interest, alignment, appeal) were also positively correlated with academic success. Reliability analysis confirmed the internal consistency of the scales, and regression analyses demonstrated that both achievement emotions and user experiences significantly predict academic performance. Recommendations for educators are to create assignments that minimise cognitive load, maximise positive user experiences, and support students’ intrinsic motivations.