Examples
Meaning
〜ことにする means the speaker or subject decides to do something. 〜ことになる means something has been decided, arranged, or resulted from circumstances.
Formation
Both patterns use the dictionary form or negative form of a verb before こと. Use ことにする for personal decision and ことになる for external or collective decisions.
Usage
Use 〜ことにする for choices such as deciding to study every day or not go on a trip. Use 〜ことになる for company decisions, school schedules, family arrangements, and assignments.
Nuance
The difference is agency. 〜ことにする shows that the subject chose. 〜ことになる avoids emphasizing the decision-maker and often sounds more objective or indirect.
Comparison
大阪へ行くことにしました means I decided to go to Osaka. 大阪へ行くことになりました means it has been decided that I will go to Osaka. The second sentence may imply work, family, or another circumstance decided it.
Common Mistakes
A common mistake is translating both as decided and ignoring who decided. In Japanese, this distinction strongly affects the nuance of the sentence.
Related Grammar
〜ことにする
〜ことにする means to decide to do or not do something. It emphasizes the speaker's or subject's own decision.
〜ことになる
〜ことになる means that something has been decided or arranged, often by circumstances, a group, or someone other than the speaker alone.
〜ことになっている
〜ことになっている describes a rule, arrangement, schedule, or established decision that is already in place.
〜ようにする
〜ようにする expresses making an effort, setting a habit, or trying to make sure something happens or does not happen.