ないと

ないと at the end of a sentence means "I have to", "I need to". It is ないといけない with the ending dropped, and it goes after the ない-form of a verb. It belongs to casual speech, and most often you say it to yourself.

• × 行くないと → 行かないと

"If you don't…"

The と is the conditional と, so ないと literally means "if I don't". When the sentence goes on, the second half says what happens then.

The full forms

The dropped ending is いけない or だめ. Spelling it out makes the obligation firmer, and いけません or だめです makes it polite.

For "must not", Japanese uses てはいけない instead.