If you’re learning Japanese, you’ve probably come across the phrases 「〜ことになる」 and 「〜ことにする」. They look super similar, right? But they have different meanings and are used in different situations.

Let’s break them down in a simple and clear way so you can start using them with confidence!

What’s the difference?

〜ことになる = It has been decided that… / It turns out that…
Use this when a decision is made by someone else or by circumstances (not you!).

〜ことにする = I’ve decided to…
Use this when you decide something yourself.

Think of it like this:

Example Sentences

◎〜ことにする (You decided it)

1. 毎日日本語まいにちにほんごを勉強べんきょうすることにしました。
   → I decided to study Japanese every day.
2. 今年ことしの夏なつは旅行りょこうに行いかないことにしました。
   → I’ve decided not to travel this summer.
3. 甘あまいものを食たべすぎないことにしています。
   → I make it a habit not to eat too many sweets.
   (Used in the present continuous to show a personal rule or habit.)

◎〜ことになる (Decision made by others or situation)

1. 来月らいげつ、日本にほんに転勤てんきんすることになりました。
   → It’s been decided that I’ll be transferred to Japan next month.
2. 大学だいがくを辞やめることになりました。
   → It turns out I’m going to quit university.
   (This can imply a decision influenced by outside circumstances.)
3. 会議かいぎは中止ちゅうしされることになりました。
   → It has been decided that the meeting will be canceled.

Similar Sentences – What’s the Nuance?

Sometimes you’ll see two sentences that are both grammatically correct, but they have slightly different meanings or feeling depending on who made the decision.

Let’s look at an example:

会社かいしゃを辞やめることにしました
→ I decided to quit my job.
→ This shows it was your own decision.

会社かいしゃを辞やめることになりました
→ It has been decided that I’ll quit my job.
→ This implies that other factors or people were involved in the decision — it wasn’t necessarily your own will.

Both are natural and correct — just pick the one that fits the situation you’re talking about!

Try it Yourself! – Quick Quiz Time

Let’s see how well you understand the difference between 〜ことにする and 〜ことになる! Choose the correct answer or translate the sentence. Answers are at the bottom — no peeking!

① Choose the correct one:

来月らいげつからヨガを始はじめる＿＿＿＿。

a) ことにしました
b) ことになりました

② Translate into Japanese:

I’ve decided to eat more vegetables.

③ Choose the sentence that implies it was not your personal decision:

a) 海外かいがいに引ひっ越こすことにしました。
b) 海外かいがいに引ひっ越こすことになりました。

④ What’s the nuance difference?

Explain the difference in feeling between:

• 毎日運動まいにちうんどうすることにしました。
• 毎日運動すまいにちうんどうることになりました。

⑤ Translate into English:

新あたらしいプロジェクトを担当たんとうすることになりました。

Answers:

① a) ことにした → You made the decision to start yoga.

② 野菜やさいをもっと食たべることにしました。

③ b) 海外かいがいに引ひっ越こすことになった → It suggests outside circumstances played a role.

④ ことにしました = You chose to start exercising.

    ことになりました = Something (like doctor’s advice or company suggestion) led to that.

⑤ It has been decided that I will be in charge of a new project.

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