If you want to get admission in IITs, NITs, IIITs, GFTIs then you should have minimum 75% and 65% as a reserved category to apply for IT JEE entrance exam & to apply for BITSAT also you should have minimum 75% to apply then you should go for improvement exam.

But if you are interested in other Engineering colleges except IIts, NITs, IIITs, GFTIs then you can apply for JEE, there are many colleges like DTU, IGDTUW and NSITetc. which minimum eligibility to apply is 60%.

CBSE improvement exam application form is expected in the last week of September or First week of October.

Good Luck!