The main difference between B.Tech and M.Tech is the level of study. B.Tech is an undergraduate course that you do after 12th grade, usually for 4 years, where you learn the basics of engineering. M.Tech is a postgraduate course done after B.Tech, usually for 2 years, where you study advanced and specialized topics in engineering. B.Tech helps you start your career, while M.Tech helps you become an expert and can lead to better jobs or research opportunities.