This study aims to determine the effect of flipped classroom learning with online strategies on the ability to understand mathematical concepts and self-efficacy of seventh-grader students in SMP Negeri 1 Purbalingga in the 2021/2022 academic year. The type of research used is quasi-experimental research. The population in this study were seventh-graders from 9 different classes. Seventh-graders A and B were sampled using the cluster random sampling technique, with seventh-graders A following the flipped classroom learning with online strategy and seventh-graders B following traditional learning. The test instrument was a post-test description, which was used to measure the capacity to comprehend mathematical concepts, while the non-test instrument was a questionnaire that measured self-efficacy. The research design used is a post-test-only control design. Hypothesis testing was done by an independent sample t-test with a significance value of = 0.05. Based on the results of the study, it was concluded that flipped classroom learning with online strategies had an effect on students' ability to understand mathematical concepts, but had no effect on students' self-efficacy.