Dear Aspirant

Hope you are doing well

Actually itsdepends on you if you can study yourself in home with online preparations and previous year papers then its good because there is various online platform which help you to study online and if you can't then i suggest you to go for offline classes

First check the syllabus and try to cover important topics with high weightage

And According to me 3 to 6 months is enough for you to crack it

To know more about syllabus https://www.google.com/amp/s/competition.careers360.com/articles/nda-syllabus/amp

If you want to know more about it check out the link given in below https://www.google.com/amp/s/competition.careers360.com/articles/nda/amp

And previous year question papers link https://competition.careers360.com/download/nda-sample-papers-previous-years?sort=recommended?icn=NDA_sample_paper&ici=NDA_article_view_sticky_header