ことにする (koto ni suru) Meaning Japanese Grammar - Decide To

Author Anna Baffa Volpe for article 'ことにする (koto ni suru) Meaning Japanese Grammar - Decide To'

Anna Baffa Volpe

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ことにする (koto ni suru) Meaning Japanese Grammar - Decide To

The expression ことにする (koto ni suru) means decide to do something and it is also used in the past tense have made the decision to do.

In a previous post we studied the form ことになる used for actions that don't depend on our will, but occur as a result of external decisions and circumstances.

In this post we learn more about the meaning of ことにする, how it is formed and when ことにする is used through real example sentences.

ことにする, decide to do something

With the expression ことにする we talk about something we decide to do or we decided to do by our will, we chose or choose to do that action.

自分の意志, our own will


I have decided to travel abroad..

How ことにする is formed

The expression ことにする is formed:

  • by the noun (こと) thing, matter, situation
  • by the particle に
  • and by the verb する do
B3 or dictionary form+ことにする


Today I'll go to bed early.

Past tense

We use the past tense to express actions decided before the moment of speaking.

I decided that: we use the past tense of the verb する.

  • plain form ことにする ⇨ ことにした
  • and polite form ことにします ⇨ ことにしました


I have decided to go to Japan to study.

する and なる: do and become

It is important to compare these two verbs used in many Japanese expressions.

  • する is the transitive verb do, it is translated doing something
  • なる is intrasitive and means become, therefore it refers to something that depends on external causes

We find the same nuances in the expression we are analysing:

  • ことになる indicates something that occurs due to external causes, comes from situations and decisions external to us: it is deduced that, it emerges that, it is decided that.
  • ことにする is personal and indicates something we decide and plan: decide to.

Negative form:

The negative form applies to the verb preceding こと and uses the suffix ない.

Plain Form negative with the suffix ない+ことにする


I have decided not to go to the party.


I'm tired today, so I won't go out.


I have decided not to drink coffee before going to bed.

ことにしている and the regular practices

ことにする is also used in the form ている, that is the て form of the verb and the auxiliary いる.

It is used to describe actions that one decides to perform with regularity and that are part of one's daily routine.


I go jogging 30 minute every day (as a regular practice).

Let' pretend that...

ことにする has another nuance of meaning in Japanese that we can translate let's pretend that.


Let's pretend we didn't see it!

In this case we can find the verb preceding こと in the past tense.

Examples of ことにする


Our company has decided to establish a branch office in America.


I drink herbal tea once a day.


In the meantime, I'll stay at the hotel.