What Duolingo score do you need for Montana State University Billings?

Both pages list Duolingo 100 in their test tables. The graduate page says official results can be sent to Admissions and Records, Attn: International Admissions. Neither page gives a Duolingo validity period or subscore rule.

For comparison, the undergraduate page sets IELTS at 6.0 and the graduate page sets it at 6.5.

Undergraduates who are academically qualified may be awarded conditional admission; completing an intensive English programme then satisfies the requirement. Graduate applicants may be considered for provisional admission with required attendance in the Intensive English Language Program (IELP). Completing set levels at partner language schools, such as level 112 at ESL Language Centers, also counts for undergraduates.

Requirements vary by programme and change between admissions cycles. The score that binds you is the one on your MSU Billings programme page and in your offer letter, so check it there before you book a test.