To decide to do, promise to do
-기로 하다 expresses the making of a promise with another person and is made by adding -기로 to the verb stem.
-기로 하다 can also express the making of a promise with oneself. That is, it can express a decision or resolution to do something. It is made by adding -기로 했다 to the verb stem.
While -기로 하다 is mainly used in its past tense forms of -기로 했어요/했습니다, it is sometimes used in its present tense form of -기로 해요. In such cases, it refers to the speaker and listener making a promise to do something.
Used to make a promise with another person or oneself.
While 기로 하다 is mainly used in the past tense form, it is sometimes used in its present tense form. In such cases, it refers to the speaker and listener making a promise to do something.