Dear Mohan, 

For jee  mains

• You can attempt jee mains for 3 times and that also in consequetive years after your 12th boards. From 2019 you can give the exam 2 times in a year as announced by NATA which means in 3 years 6 times. 
• If you have given exam for 2 years already eg. 2017 and 2018 then this year you can give 2 times and this is your last attempt. 

For jee advanced 

• Students can attempt JEE Advanced exam for maximum two times in consecutive years after 12th . You give the exam or not doesn't matter . In 12th and year after 12th is considered for giving jee advanced  exam. After that no chance. 

Hello Mohan 

You can give jee mains in consecutive 3 years ( 6 papers 2 in each year ).

And jee advanced you can give in 2 consecutive year .

Like if you give jee mains in 2019 than you can give in 2020 and 2021 

Similarly jee advance if you give in 2019 than you can give only in 2020 further.

So good luck 

Hi

JEE Mains can be taken for maximum 3 times and from 2019 onwards, JEE Mains is held twice a year. So, total 6 times. Whereas JEE Advanced only 2 times.

All the best.

Hope this helps.

Cheers!