Purpose: This study aims to test whether there is an effect of mastery of the concept of mathematical fractions on students' understanding of the calculation of inheritance. Methods - Data were collected through a test on two parts of the question: mathematical fractions and a test of inheritance calculations on 66 students majoring in Islamic Religious Education (PAI). The analysis technique used is correlation and regression. Findings- Through data analysis, it can be concluded that the two are indeed interrelated and mastery of the material fraction concept has a 40% influence proportion on students' ability to calculate inheritance. These results indicate that to support students' ability to calculate inheritance and be equipped with fiqh knowledge, they also need to be fitted with their ability to calculate, especially in mathematical fraction functions. Limitations - This study is limited to a sample of PAI students with Fiqh concentration class 2014, so it does not describe all students at Antasari Islamic University. Future studies are advised to expand the sample size and add more math fraction tests to show students' real abilities.