i have scored 89% in 10 ,58% in 12 and 73% in graduation , what are chances to get iim and how much i have to score in cat.

Dear

According to your query you need to score above 85 percentile and should perform well in GD and pi session.

Your academic record is good just you need to get good marks in cat and maintain performance in GD and pi .

All the Best

Hi, I understand your query. Your academics is not that great as per selection criteria in many management institutes. Also you will have to really work hard on your overall CAT profile and percentile to get into top b schools because of lack in school academics.
Also just do not rely on one exam, give as many you can like MAT, CMAT, XAT, May MAT etc.
Take coaching if you are unable to do it by self. That is okay.
Focus on getting 99 above percentile and for interviews as well (PI rounds).
Do not lose hope focus on your other aspects of selection.
All the best.