The purpose of this development research is to create a self-efficacy instrument to assist students learning mathematics that is valid, practical, and reliable. A self-efficacy questionnaire is the format of the instrument that was created. The main driving force behind this research is the scarcity of empirically validated self-efficacy surveys for studying mathematics in different parts of Indonesia. Students' self-efficacy is important since it affects how well they learn. This research used the ADDIE development technique as its methodology, comprising five stages: Analysis, Design, Development, Implementation, and Evaluation. Readability, validity, and reliability tests were used to test the data empirically and theoretically through expert evaluation. Both qualitative and quantitative analyses were done on the data; expert validation results and readability test results were subjected to a qualitative analysis, while validity and reliability test results were subjected to a quantitative analysis. Students from different schools in Indonesia took the quantitative test. At least ten times as many statements were included in the sample size that was used. 36 statement items were originally developed throughout the development phase; however, item 33 was split into two distinct statements, resulting in 37 questionnaire items that represent students' self-efficacy in learning mathematics. This designed questionnaire can be used to evaluate Indonesian students' self-efficacy in learning mathematics at the junior and senior high school levels.