What Duolingo score do you need for ISM University?

The page does not state a validity period, subscores or how to send Duolingo results. After the motivational interview, the bachelor's admission commission can ask you to take the ISM English language test.

For comparison, the same page sets IELTS at 6 for bachelor's and IELTS Academic 6.5 with no section below 6.0 for master's.

ISM runs its own English test, accepted at 55 for bachelor's and 70 for master's. Bachelor's applicants whose previous education was entirely in English may be exempted. Master's applicants may be exempted with education completed entirely in English, a qualifying Erasmus or exchange semester taught in English, or employer-certified work in English, subject to the admissions committee.

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