We can use the noun こと (thing/matter) with the verb “to become” (成る) to express that a decision has been made. Here, the meaning is that “it has been decided that…” and is used specifically when the outcome is something that you haven’t decided yourself (e.g., a company decision, a group consensus, or fate).
| 来週は、出張へ行くことになりました。 |
| It has been decided that I will go on a business trip next week. (Literal: Next week it has become the thing that I am going on a business trip.) |
JLPT Contrast (にする vs. になる): Exams frequently test the difference between your own active decisions and decisions made for you.
Often the verb “to become” takes the continuous/state form (〜ている), which roughly translates as “it is supposed to be such that” or “it has been arranged that.” It is heavily used to state that the prior clause is a rule, custom, or schedule that must be followed.
～ことになっている is JLPT N3 grammar. It can be used in both writing and conversation, though there are more formal ways of creating this expression.
| うちの会社では、パソコンをなくすと謝罪文を書くことになっています。 |
| In my company, it is a rule that you must write an apology letter if you lose your computer. |
| こちらではタバコを吸えないことになっているので、ご協力お願いします。 |
| It is a rule that you cannot smoke here, so we ask for your co-operation. |
| 私がいないときに荷物が届いたら、宅配ボックスに入れてもらうことになっています。 |
| If a parcel arrives at a time when I’m not home, it is arranged so that they put it in the delivery box. |