Many Muslim women still do not understand the laws of menstruation and istihadhah properly. A thorough understanding is needed for better quality of worship and reproductive health. However, related information is often difficult to access or of little interest to many users. Therefore, as an increase in effectiveness and practicality, this can be channelled through Android applications, which are now increasingly accessible to the public. The planning of the menstruation and istihadhah calendar application is designed to contribute to the spread of understanding and ease in recognizing each menstrual cycle. The research model used is System Development Life Cycle (SDLC). The testing consists of black box testing, hardware compatibility testing, material expert testing, and user testing. The results of black box testing and hardware compatibility show that the application is lightweight and runs optimally. In material expert testing, getting 73.33% has a good and validated value. User testing gets a value of 74% which indicates good acceptance and can be accepted by users. Based on the research conducted, it can be concluded that the application runs well and can be useful as one of the contributions to the study of understanding the fiqh of menstruation and istihadhah which has an important role regarding the obligation to worship.