なければいけない

The structure なければいけない expresses obligation or necessity, meaning "must do" or "have to do" something. It conveys that not doing the action would be problematic or unacceptable.

To form it, take the ない-form of a verb, drop ない, and add なければいけない.

• いく行く → 行かない → 行かなければいけない
• たべる食べる → 食べない → 食べなければいけない
• する → しない → しなければいけない
• くる来る → 来ない（こない） → 来（こ）なければいけない

Literal meaning

The structure is literally a double negative: "if one does not do X, it won't do" (i.e., it's no good). The なければ part means "if not," and いけない means "it won't work / it's not acceptable." Together, they create a strong sense of obligation.

Polite form

To make it polite, change いけない to いけません.

Related forms

Several similar expressions exist in Japanese for expressing "must":

• なければならない – slightly more formal and stiff; common in writing and rules.
• なくてはいけない – similar meaning, uses なくては instead of なければ.
• ないといけない – more casual and conversational.
• なきゃ（いけない） – very casual, spoken shortening of なければ. Often いけない is dropped entirely:
  もういかなきゃ行かなきゃ。

  I gotta go.

Nuance

なければいけない describes obligation from external circumstances, rules, or necessity – not personal desire. It often implies that the speaker has no choice or that the situation demands the action.