Neither the Academic IELTS test nor the General IELTS test has a passing score. Your performance in each section will be rated on a band scale of 1 to9. All educational institutions set their own minimum IELTS scores eligibility for foreign students seeking admission. Similarly all countries have their own minimum band requirement for foreign nationals looking to migrate.
Even if you are good at English and have been scoring good marks/grades in your school or college English exams it is advisable to prepare for the IELTS test because there is a gigantic difference between the scoring pattern of IELTS and the regular English exams which you may have been writing in your school or college.