Is Harvey Mudd harder to get into than Duke overall?

No. In an overall, big-picture sense, Duke is typically harder to get into than Harvey Mudd. Duke draws a much larger national and international applicant pool across many majors, has broader name recognition, and is one of the most sought-after private universities in the country. Harvey Mudd is extremely selective too, but its applicant pool is smaller and much more self-selecting because of its intense STEM focus.

One key difference is who applies. Duke attracts students interested in everything from engineering and public policy to humanities, business-related paths, and premed, so it gets a very wide range of high-achieving applicants. Harvey Mudd appeals most strongly to students who specifically want a rigorous math, science, and engineering environment, which narrows the field even though that field is exceptionally strong.

Another difference is admissions positioning. Duke operates in the same tier of national demand as a handful of ultra-prominent private universities, and many applicants treat it as a reach even with top grades and scores. Harvey Mudd has a superb academic reputation, especially in STEM, but it is more niche, and that usually makes it slightly less difficult overall than Duke in the broad admissions conversation.

For your purposes, the better way to think about it is that both are reaches for most applicants, but Duke is usually the tougher admit overall. Harvey Mudd can still feel just as hard, or harder, for students without a very strong quantitative profile because its curriculum and campus culture are so specifically STEM-centered.