Explanation
Expresses that something is supposed to be or has been decided (rule, plan, custom).
Formation
Verb-plain form + ことになっている / い-Adjective + ことになっている / な-Adjective + だ + ことになっている / Noun + だ + ことになっている
Detailed explanation
The ～ことになっている grammar point is used when something has been decided, planned, or there is a rule/custom that everyone follows. It can be translated as 'it is supposed to be,' 'it is decided,' or 'it is customary that.'
Examples
Nihon de wa, hidarigawa o unten suru koto ni natte imasu.
In Japan, it is decided that people drive on the left side.
Kaisha no kisoku de wa, seifuku o kiru koto ni natte iru.
According to the company rules, we are supposed to wear uniforms.
Kanojo wa ashita kekkon suru koto ni natte imasu.
She is supposed to get married tomorrow.
Kono shouhin wa kouhinshitsu da to iu koto ni natte imasu.
It is said (or generally accepted) that this product is of high quality.
Practice
Grammar content sourced from hanabira.org.