許可・義務N4
〜なくてもいい
don't have to do... / it's okay not to...
Structure
V-ない形（語幹）+ なくてもいい
Explanation
Attached to the nai-stem of verbs, 〜なくてもいい means "it's okay not to...", the negative counterpart of 〜てもいい, "don't have to...". In speech 〜なくていい is common.
Examples
明日は来なくてもいいですよ。
You don't have to come tomorrow.
無理に全部覚えなくてもいいです。
You don't have to force yourself to memorize everything.
Note
〜なくてもいい is the opposite of 〜なければならない. Be careful: 〜なくてはいけない means "must", not "don't have to".