The Council of Central Boards of Secondary Education (CoBSE) has compiled a list of percentage scores that separate the top 20% students from the rest in each board this year and according to them this cut off list can be used as indicators of what students need to score to be eligible to get admission to IIT. But according to Ajit Chaturvedi, head of the Delhi University statistics department the released cut off list is not reliable as score pattern varies every year. ‘’ There is no reason why scores next year should follow the pattern they followed this year,” he said.

In 2008, top 1 percentile students in Andhra Pradesh board scored more than 81.2% but in 2010 top 1 percentile student scores more than 95.2% (you can see a big difference in just two years.)
In Bihar board, the cut off percentage for top 1 percentile was 66.7% in 2008 and it was 74% in 2010. In same way cut off varies in other states also every year, so it is not realistic to predict cut off percentage to come under top 20 percentile in coming year.
One more point Mr Chaturvedi added that the human resource development (HRD) ministry has introduced the new IIT eligibility criterion requiring that students secure a spot in top 20 percent of their board with the aim of making them focus on board examinations more than at present. This is likely to make students study harder for board examinations next year, which should significantly push up the cut-off corresponding to the top 20 percent.
As per cut off release released by CoBSE cut off list of percentage for top 20 percentile in different state boards are as below:

Board		Percentage Required
Andhra Pradesh		87.2
Assam		54.2
Bihar		64.6
CBSE		77.8
Chhattisgarh		56.8
Goa		56.25
Himachal Pradesh		63.2
Jharkhand		52.4
Jammu and Kashmir		67
Karnataka		67.5
Kerala		76.5
Meghalaya		49.4
Manipur		64.6
Madhya Pradesh		64
Maharashtra		61.17
Mizoram		56.2
Nagaland		49
Orissa		56.33
Punjab		70.8
Rajasthan		63.8
Tripura		50.8
Tamil Nadu		78.17
Uttarakhand		55.2
Uttar Pradesh		65
West Bengal		58
National Open School		60.6