The answer depends almost entirely on one question: is the programme taught in Japanese or in English?
Japanese-taught programmes
Undergraduate: typically N2 as a minimum, N1 preferred. Many national universities effectively expect N1 for competitive courses. You will be attending lectures, reading textbooks and writing assignments in Japanese, so the bar reflects a real requirement rather than a formality.
Graduate: N1 in most cases, particularly in the humanities and social sciences. Some science and engineering laboratories are more flexible, especially where the research group works partly in English — but you should confirm with the specific laboratory rather than assuming.
English-taught programmes
A growing number of Japanese universities offer degrees taught entirely in English. These often require no JLPT at all, asking instead for English-language evidence.
If that is your route, be realistic about the trade: you can be admitted without Japanese and you will still be living in Japan. Part-time work, administration, housing and daily life all run in Japanese. Students who arrive with no Japanese into an English-taught programme frequently describe the first year as harder socially than academically.
N3 is a sensible practical target for that situation even when nothing formally requires it.
Do not stop at the JLPT
Two things matter as much as your level, and are often missed.
The EJU. The Examination for Japanese University Admission for International Students is what many undergraduate programmes actually use for admission — it tests Japanese as a language of instruction plus academic subjects. For undergraduate entry, the EJU is frequently the more important examination, and a JLPT certificate does not substitute for it.
The individual university’s rules. Requirements vary by institution, by faculty and by year. The university’s own admissions page for your specific programme is the only source that binds. Anything else, including this page, is orientation.
Timing
Work backwards, because the JLPT calendar is unforgiving.
The JLPT runs twice a year — July and December, with some locations offering December only — and results arrive roughly two months later. So a December sitting produces usable evidence in late January.
If an application deadline falls in, say, November, a July sitting is your last safe opportunity, and a December sitting is too late. Miss that and you wait a year, not six months. See how to register for the JLPT.
Build in a retake window. Planning a single attempt immediately before a deadline means that one bad Sunday costs you a year.
Scholarships
Many scholarships for study in Japan carry their own Japanese requirements, often at N2 or N1, and their deadlines are usually earlier than the university’s. If funding is part of your plan, the scholarship deadline is the one to work backwards from.
If your goal is work rather than study
Then this is not your route, and it is worth being clear about that. A degree is a long and expensive way to reach Japan if the destination is employment.
The Specified Skilled Worker route asks for a language qualification — JFT-Basic at 200+ or JLPT N4 — a sector skills test, and an employer. It is measured in months rather than years. See what happens after you pass for the full route.
Different goals, genuinely different paths. Choose the one that matches what you actually want.