なくてもいい

なくてもいい means "you don't have to": the action isn't required. Take the ない-form, change the final い to くて, and add もいい – 行かない becomes いかなくて行かなくてもいい.

The い of ない has to change. もいい does not go on ない itself.

• × 行かないてもいい → 行かなくてもいい

なくてもいい or てもいい

てもいい, on the ordinary て-form, gives permission: "you may". なくてもいい lets someone off: "you don't have to".

Asking and answering

"Do I have to?" is a question with なければなりませんか, and "no, you don't" is answered with なくてもいい. Asking with なくてもいいですか is asking to be let off.

を often becomes は

The thing you are let off often becomes the topic, so を turns into は: this one, at least, you can skip.

Usage notes

These go beyond the verb with もいい.

Casual forms

Among friends, です goes, and often も as well: なくていい. なくてもだいじょうぶ大丈夫 says the same thing.

Adjectives and nouns

An い-adjective goes to 〜くなくても, and a noun or な-adjective takes じゃなくても.