～に決まっている — I'm Sure It Must Be
Expresses the speaker's strong conviction that something is certainly the case, based on personal judgment or common sense. It is more subjective and emphatic than はずだ — closer to 'obviously' or 'of course'. Common in casual, assertive speech.
Structure
[Plain form (na-adj/noun without だ)] + に決まっている
Examples
そんな高い店、まずいわけがない。おいしいに決まっている。
Sonna takai mise, mazui wake ga nai. Oishii ni kimatte iru.
A place that expensive can't be bad — it's got to be delicious.
い-adjective おいしい + に決まっている asserts strong certainty from common sense.
こんな時間に電話したら、迷惑に決まっているよ。
Konna jikan ni denwa shitara, meiwaku ni kimatte iru yo.
Calling at this hour is obviously going to be a nuisance.
な-adjective 迷惑 (no だ) + に決まっている conveys the speaker's firm judgment.
彼が犯人に決まっている。
Kare ga hannin ni kimatte iru.
He's definitely the culprit.
Noun 犯人 (no だ) + に決まっている expresses the speaker's certain conviction.
• Register: casual / conversational; sounds assertive or even pushy. • Based on the speaker's subjective certainty, not on solid evidence. • Note: no だ before に決まっている for nouns and な-adjectives.
Commonly confused with
The JLPT rarely asks whether you recognise a pattern — it asks which of several similar patterns fits. These are the ones ～に決まっている is tested against.
vs はずだ
に決まっている is subjective, emotional certainty ('obviously!'); はずだ is a logical expectation based on reasoning or evidence and sounds more objective.
vs に違いない
に決まっている is casual and highly emphatic common-sense certainty; に違いない is a more formal, reasoned deduction ('must be').
More modal expressions
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