Translation guide
The English word "optional" means something is not required and can be chosen freely. In Japanese, this concept is expressed through adjectives, nouns, and set phrases that indicate choice, non-compulsion, or the ability to do without.
Describing something (a feature, item, action) that is available but not mandatory.
A formal noun/adjective meaning 'optional', 'voluntary', or 'at one's discretion'. Common in official contexts, forms, and technical settings.
参加は任意です。
Participation is optional.
任意の項目を入力してください。
Please fill in the optional fields.
A casual phrase meaning 'it's okay not to have/do'. Very common in everyday speech for saying something is optional.
傘はなくてもいいよ。
An umbrella is optional (you don't need one).
返事はなくてもいいです。
A reply is optional.
A slightly more formal version of なくてもいい, meaning 'it doesn't matter if you don't have/do'. Polite and common in service situations.
予約はなくても構いません。
A reservation is optional.
Loanword from English, used for optional extras, features, or choices, especially in products, services, and technology.
この機能はオプションです。
This feature is optional.
オプションで保険を追加できます。
You can add insurance as an option.
Literally 'choice system', used for systems where something is optional, like elective courses or optional benefits.
この科目は選択制です。
This subject is optional.
Referring to add-ons, accessories, or features that cost extra or are not part of the standard package.
Means 'sold separately'. Used for optional accessories or parts not included with the main product.
ケースは別売りです。
The case is optional (sold separately).
Also used for optional extras that may cost more, like car options or menu add-ons.
任意 is a formal, written term often used in documents, forms, and rules. オプション is a casual loanword common in everyday conversation about products and services. For 'you don't have to', use なくてもいい in casual speech.
記入は任意です。
Filling this out is optional.
デザートはオプションで付けられます。
You can add dessert as an option.
随意 (ずいい) means 'optional' in legal or very formal contexts, but it's rare and can sound unnatural. Stick to 任意 or オプション for most situations.
サンルーフはオプションです。
The sunroof is optional.