なくてもいい

1. 1Don't have to do; it is not necessary to do the action.Ex. 1
2. 2It's all right not to have something; one can do without it.Ex. 2

Used in everyday speech and writing to say that an obligation does not apply, often with a reason as in example 1, or to ask permission to skip something. It is the negative counterpart of なくてはいけない, which expresses obligation. Unlike ないほうがいい, which advises against doing something, なくてもいい simply removes the need and leaves the choice open.

• ことはないN3「ことはない」 attaches only to the dictionary form of verbs. In the sense of 'no need to do something' it can replace 「なくてもいい」, but it more actively denies the necessity and is often used to comfort or encourage the listener; it cannot express 'it's fine not to have something.'
• までもないN1「までもない」 attaches only to the dictionary form of verbs and reflects the speaker's judgment that going out of one's way to do it would be superfluous, often pairing with 「わざわざ」. 「なくてもいい」, by contrast, focuses on waiving the obligation—granting permission not to act—and can also attach to adjectives and nouns.
• には及ばないN1When it means 'no need,' 「には及ばない」 is close in sense, but it attaches to the dictionary form of verbs or to action nouns, sounds formal, and stresses that things have not reached the point where doing so is required. It can also mean 'not measure up (to something),' a sense that cannot be replaced with 「なくてもいい」.
• にあたらないN1「にあたらない」 is also rendered 'no need,' but it attaches only to reactions or evaluations such as surprise, worry, or praise, takes the dictionary form or a noun, and has a written, judgmental flavor. 「なくてもいい」 can also waive concrete actions and say it's fine to lack something, with a neutral tone.
• なくてはいけない / なくてはならないN4「なくてはいけない／ならない」 means 'must'—the exact opposite of 「なくてもいい」 ('no need')—so the two cannot be swapped. To answer 「〜なくてはいけませんか」 negatively, use 「いいえ、〜なくてもいいです」.
• 〜ないほうがいいN4「〜ないほうがいい」 advises the listener not to do something because not doing it is better, whereas 「なくてもいい」 simply says it's fine not to do, not to have, or not to be—without any dissuasion. The former is built by adding 「ほうがいい」 directly to a verb's ない形; the meanings differ, so they are not interchangeable.

なくてはいけない / なくてはならない express obligation, the opposite of なくてもいい, while ないほうがいい advises against an action; ことはない (N3) also means 'no need to' but often reassures or advises another person. までもない, には及ばない and にあたらない are more formal N1 expressions: までもない means something is too obvious to need doing, には及ばない politely declines a need, and にあたらない means something doesn't warrant a reaction (e.g. surprise).