happy to help!

The cutoff gets decided when once everyone gets to the exam and on their average score.

its a tradition off jee that :

• if the paper is tough,comparatively difficult then the cutoff would be low 
• if the paper is easy,comparatively easy then the cutoff goes high
• anyways you could refer to the previous years cutoff to get an idea about the cutoff range and it’s relation with difficulty of paper
• link provides cutoffs of previous years :https://www.google.co.in/amp/s/engineering.careers360.com/articles/jee-main-cutoff%3famp

Thank you! 

• Number of applications received for JEE Main 2018

• Number of questions asked in the paper

• Difficulty level of the exam

• Performance of the candidates

• Previous years’ cutoff trends of JEE Main

To have an idea you can check the cut off of previous year

To check the cut off of NITs you can refer below link

https://engineering.careers360.com/articles/jee-main-cutoff

Good Luck!!