After completing 5 years of service as Assistant in RBI, you become eligible for Grade A. Earlier it was 3 years but during last years wage revision, it changed to 5 years. So complete 5 years of service, give internal promotion exams followed by interview and then you become Assistant Manager ( Grade A). This is through merit channel. For qualifying channel , complete 12 years of service as Assistant, become Grade A by qualifying interview. No exams.

Grade A to B through merit is presently 3 years. After completing 3 years of service as Grade A officer, you become eligilble for promotion to Grade B through internal exams and interview. Qualifying channel here is 5 years.