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For any IIM, you will need more than 95 percentile. IIM A has had the following percentiles as the minimum cut offs for 2019 across all Categories.

Now the various ratings for various scores are as follows:

Now coming to the 12th, it looks like this for various Streams:

And then the Rating scores for Bachelor's degrees are as follows:

And for professional degrees, the rating scale looks like this:

And then work experience is considered too for those Candidates who have it. The scores from each level of studies are added up. And the no.of Candidates shortlisted per each Category will be as follows:

UR: 100

NC-OBC, Trans: 57

SC: 32

ST: 16

PWD: 6

And after being shortlisted based on these criteria, Candidates have to be shortlisted also for WAT and PI rounds. The whole process can be checked at their page: https://www.iima.ac.in/web/pgp/apply/domestic/admission/selection-process

IIM BANGALORE:

IIM B has a 2 phase selection process and the selection criteria are applied in 2 phases. For admission to IIM B, your CAT score alone is considered for finalizing  the first short list. Consistent good academic record starting from secondary school, higher secondary, Graduation etc are considered. Also CAT section wise scores are also considered along with relevant work experience. But CAT score is considered as the minimum level of proficiency that IIM -B expects from Candidates to be shortlisted. CAT 2019 cut offs for admission to batch of 2020-22 for IIM B were as follows:

During phase 1, all those Candidates shortlisted based on the cut offs will be called in for Personal Round of Interview. Here the panel will evaluate each Candidate based on Academic Background, quality of work experience, etc. Those who clear this round will have to take a Writing Ability Test. The topic will be given by IIM B. The topics might range from issues and developments related to socio-political, economic and business affairs, sports, etc which require your creative thinking. This round is approximately for 30 minutes. The Pre- PI, Interview and WAT scores will be used for second phase.

In phase 1, the Candidate's percentage scores in their 10th and 12th exams are adjusted by dividing each score by 90th percentile score obtained in that board. For this purpose, data base of CAT applicants of the past 2 years is considered. After this, an adjusted score is calculated based on the final score obtained in the Bachelor's degree. The final shortlisting weightage is as follows:

CAT = 40
10th board = 20
12th board = 10
Bachelors = 20
Gender Diversity = 2
Work Experience = 8

The 40 points for CAT are derived from the performance in each of the three sections as follows:
Verbal & Reading Comprehension - 14 points
Data Interpretation & Logical Reasoning - 16 points

Quantitative Aptitude - 10 points.

The WAT score with a weightage of 10 and the personal interview score with a weightage of  30, after standardization across interview panels and sessions, will be added for a final aggregate score. And that looks like this:

CAT (weight = 25)

10th board (weight = 10

12th board (weight = 5)

Bachelors (weight = 10)

Weighted Work Experience (weight = 10).

This answer covers pretty much everything regarding IIM B admission process. For any more information, please read the official article: https://www.iimb.ac.in/sites/default/files/inline-files/PGP-admission-process-2020-22.pdf

IIM Calcutta:

And the final selection is based on:
CAT 2020 Score 30
Personal Interview 48
Written Ability Test 10
Academic Diversity 04
Work Experience 08
Total 100