Online learning is one of the learning designs considered more efficient in terms of time, as it can be done anywhere and anytime. This study investigates two factors that may influence mathematics achievement in the context of online learning: self-regulated learning and self-efficacy. The researcher aimed to explain the relationships between online learning and mathematics achievement, self-regulated learning and mathematics achievement, self-efficacy and mathematics achievement, self-regulated learning and online learning, self-efficacy and online learning, self-efficacy and online learning with mathematics achievement, and self-regulated learning and online learning with mathematics achievement. The validity of the research instrument was first tested through expert judgment. The sample consisted of grade VIII students from schools implementing the new curriculum in Indonesia. The data were analyzed using Structural Equation Modeling (SEM). The results showed that mathematics achievement is directly influenced by online learning, self-regulated learning, and self-efficacy. Furthermore, when online learning acts as a moderating variable, mathematics achievement is also indirectly influenced by self-efficacy and self-regulated learning.