The numeracy of 10th-grade students at SMAN 3 Slawi is still not optimal and needs improvement. This is because students are not accustomed to dealing with non-routine problems. This research aims to determine the effectiveness of the STEM-based MURDER learning model assisted by Quizizz in improving students' numeracy. In this study, the proportion test of student completeness obtained a Sig. value of 0.004, indicating that the proportion of students class experimental exceeded the classical completeness, reaching 42%. In the test of average differences, a Sig. value of 0.004 was obtained, meaning that the numeracy ability of the experimental group was higher than control group. In terms of improvement, the N-Gain test resulted 0.28, which falls into the interval 〈g〉 < 0.3, indicating that the improvement in students' numeracy using the STEM-based MURDER learning model assisted by Quizizz is relatively low.