に決まっているni kimatte iru“it must be; surely”

に決まっている means it must be; surely. It is a JLPT N2 Japanese grammar pattern used to express strong certainty based on assumption or attitude.

This grammar point often appears in advanced reading, formal writing, notices, essays, and careful conversation. If you want to read Japanese with more nuance, に決まっている is a useful pattern to learn because it shows the speaker’s logic, stance, or emphasis.

What does に決まっている mean?

Use に決まっている when you want to express strong certainty based on assumption or attitude.

Natural translations include:

• it must be; surely
• depending on context
• in a way that matches the speaker’s emphasis

How to form に決まっている

Plain form + に決まっている

Examples of the pattern:

• 彼なら合格するに決まっている。
• こんなに安いなら
• 何も準備していないのだから

When is に決まっている used?

Use に決まっている in situations like:

• reading formal explanations, announcements, or essays
• making a point more precise than a basic grammar pattern would
• connecting two ideas with a clear nuance

Tone and register:

• usually neutral to formal
• common in JLPT N2 reading passages, news, notices, and business-like writing

に決まっている example sentences

• 彼なら合格するに決まっている。 — If it’s him, he is sure to pass.
• こんなに安いなら、すぐ売り切れるに決まっている。 — If it’s this cheap, it will surely sell out quickly.
• 何も準備していないのだから、失敗するに決まっている。 — Since nothing has been prepared, it is bound to fail.
• 毎日練習している彼女が上手になるに決まっている。 — She practices every day, so of course she’ll improve.
• そんな言い方をしたら、相手が怒るに決まっている。 — If you say it like that, the other person is sure to get angry.

After reading each sentence, ask what job に決まっている is doing. Is it limiting, adding, conceding, asserting, or describing a condition?

Nuance of に決まっている

The key nuance is express strong certainty based on assumption or attitude.

For example:

• In formal writing, に決まっている often sounds more precise than a casual equivalent.
• Compared with に違いない, it has a different tone or scope even when the English translation looks similar.

に決まっている vs に違いない

に決まっている:

• fits the N2 nuance explained above
• often sounds more specific, formal, or emphatic

に違いない:

• is usually broader, simpler, or used in a different register
• may be better in casual conversation depending on the sentence

Quick contrast examples:

• 彼なら合格するに決まっている。
• Try rewriting the sentence with に違いない and notice whether the tone or meaning changes.

Common mistakes with に決まっている

Watch out for these mistakes:

• Translating it too literally and missing the function in context
• Confusing it with に違いない just because the English translation overlaps
• Using it in casual speech when a simpler pattern would sound more natural

A helpful practice method is to write one sentence with に決まっている, then compare it with a related grammar point. Explain the difference in your own words.

Is に決まっている on the JLPT?

Yes. に決まっている is commonly taught as JLPT N2 grammar.

That means learners should be able to:

• recognize it in reading
• understand its nuance in context
• use it in simple original sentences

Practice questions for に決まっている

• Write one sentence that clearly needs に決まっている.
• Write a second sentence with に違いない and compare the nuance.
• Find a notice, article, or dialogue where this kind of meaning would be natural.

Learning path for に決まっている

To learn に決まっている efficiently, follow a path that matches this pattern’s real function.

1. First review the formation so the base structure feels natural.
2. Then compare に決まっている with に違いない and the related lessons below.
3. Finally, write your own sentence where the context makes に決まっている necessary.

Related grammar to review next

• n3 ni chigai nai — must be; no doubt.
• に相違ない — without a doubt; certainly.
• n4 hazu da — should be; expected to be.

Learn に決まっている with Hane

If you want to review に決まっている together with the related patterns above, Hane helps you connect grammar, kanji, and vocabulary in short, focused sessions.

Browse more lessons here:

• All grammar lessons
• JLPT N2 grammar lessons