Is MIT harder to get into than Tufts?

Yes. MIT is harder to get into than Tufts overall, and not by a small margin. Both schools are highly selective, but MIT sits in a different tier of admissions difficulty because of its much smaller class, unusually intense applicant pool, and very strong concentration of students with top-level math, science, and engineering preparation.

For a student deciding how to categorize them on a college list, MIT should be treated as an extreme reach for nearly everyone. Even applicants with outstanding grades, top scores, major research, Olympiads, or other exceptional STEM achievements are never close to guaranteed there. Tufts is also very competitive and should still be considered a reach or high reach for many students, but it is more attainable than MIT in a broad, overall sense.

The applicant pools also feel different. MIT attracts a very high share of students who are specifically aiming at elite STEM programs and who often have unusually advanced quantitative backgrounds. Tufts draws many excellent applicants across disciplines, including pre-med, international relations, engineering, and the humanities, but its admissions bar is not as singularly compressed at the very top.

So if your question is simply which school is tougher to enter overall, the answer is MIT. Tufts is still selective enough that nobody should treat it casually, but MIT is one of the most difficult undergraduate admissions outcomes in the country.