決まる vs 決める
JLPT N4 vocabulary · what is the difference?
Both translate as "decide", so ignore the English and look at the particle: 決まる (きまる) means something gets settled with no decider named and takes が — 日が決まりました, the date has been decided. 決める (きめる) means a person decides something, and that takes を — 私が日を決めます, I'll decide the date. This が/を split is the general rule for every Japanese intransitive/transitive pair.
When to use each
決まる
きまる
Use 決まる to report that something is now fixed, without saying who fixed it. The thing settled takes が. English renders it as "has been decided" or "is set", which is why it feels passive.
旅行の日が決まりました。
りょこうのひがきまりました。
The date of the trip has been decided.
会議は三時に決まりましたよ。
かいぎはさんじにきまりましたよ。
The meeting has been set for three.
決める
きめる
Use 決める when a person makes the decision. What is decided takes を, and the decider is the が subject. Asking someone to choose is always 決める.
何を食べるか決めてください。
なにをたべるかきめてください。
Please decide what you want to eat.
出発の日は私が決めます。
しゅっぱつのひはわたしがきめます。
I'll be the one to decide the departure date.
Sentences where only one works
予定が決まりました。
よていがきまりました。
The schedule has been decided.
予定 takes が, so you are reporting the outcome. Nobody is credited or blamed.
予定を決めました。
よていをきめました。
I decided the schedule.
Same schedule, but を means you did it. The particle alone changes who is responsible.
新しい社長が決まりました。
あたらしいしゃちょうがきまりました。
The new president has been chosen.
Announcing a result. 決めました here would sound like you personally appointed them.
毎週月曜日に掃除をすることに決まっています。
まいしゅうげつようびにそうじをすることにきまっています。
It's the rule that we clean every Monday.
〜ことに決まっている is the standing-rule use of the intransitive verb: the rule stands, nobody is deciding it now.
Common mistakes
私は明日の予定が決まります。
私は明日の予定を決めます。
If you are the one deciding, the thing decided takes を and the verb is 決める. With が you are only saying the schedule is getting settled.
日にちを決まりました。
日にちが決まりました。 / 日にちを決めました。
決まる cannot take an を object. Use が決まる to report the result, or を決める to say you decided it.
もう決めましたか。 (asked about a schedule someone else controls)
もう決まりましたか。
Asking whether something has been settled — not whether the listener personally chose — takes 決まる. 決めましたか puts the decision on them and can sound pushy.
Frequently asked questions
Both mean "decide", so how do I pick?
Ask whether a person is doing the deciding in your sentence. If yes, the thing decided takes を and you use 決める. If you are only reporting that it is now fixed, it takes が and you use 決まる. The particle test is far more reliable than the English.
Why does 決まりました sound passive in English?
Because English has no plain intransitive "decide". 決まる is not a passive form — it is its own verb, like 開く beside 開ける. You meet the same mismatch with 続く/続ける.
What does 決まっている mean?
It means something is already settled or is the standing rule: 会議は三時に決まっています, the meeting is set for three. It describes the state that 決まる leaves behind.