As of now, IIM Indore is the only IIM to have an undergraduate course which is a five-year post graduate diploma called Integrated Programme in Management (IPM). It has the same eligibility criteria as 12th standard. Candidates need to score 60% marks in HSC or 10+2 for general category and 55% for reserved category students. IIM Calcutta doesn't have this provision. So, you can't take admission into IIM Calcutta after class 12th.

Good luck.