Abstrak Usaha Mikro, Kecil, dan Menengah (UMKM) mempunyai kewajiban untuk membayar pajak setiap tahunnya. Namun, masih ada kendala terkait pencatatan dan pelaporan pajak. Oleh karena itu diperlukan bantuan teknologi seperti aplikasi kalkulator pajak. Metode penelitian mengikuti model pengembangan perangkat lunak Waterfall meliputi Analisa sistem, desain sistem, pengkodean, pengujian black box dan pemeliharaan. Hasil penelitian berupa aplikasi kalkulator pajak yang dirancang menggunakan bantuan use case diagram dan activity diagram. Abstract Micro, Small, and Medium Enterprises (MSMEs) have the obligation to pay taxes every year. However, there are still obstacles related to tax recording and reporting. Therefore it requires the help of technology such as the application of a tax calculator. Research methods following the Waterfall software development life cycle include System analysis, system design, coding, black box testing and maintenance. The results of the study are in the form of a tax calculator application designed using the help of use case diagrams and activity diagrams.