How to Say “Must Do” in Japanese | Using なければ／なきゃ + いけません

Yes! It’s another version, more formal: 行かなくてはいけません = I must go
But it’s longer, and beginners usually stick with ～なければいけません.

If you want to say “don’t have to,” you can say:
いかなくてもいいです = You don’t have to go

Yes, like: いかないといけません。
It’s short, casual, and means the same as なきゃいけません.

Both mean “must do” or “have to do” and are generally interchangeable in terms of politeness and meaning. Some nuances people sometimes feel (though not strict rules) are:

• なりません might feel slightly stronger or emphasize necessity arising from rules, logic, or circumstance (“it becomes necessary”).
• いけません might feel slightly more related to social rules or something being unacceptable if not done (“it won’t do if not”).

However, in most everyday situations, you can use either. Both have casual forms too (e.g., なきゃいけない vs なきゃならない/なんない).

いけません comes from the potential negative form of the verb 行く (iku – to go), which is 行けない (ikenai). While 行けない can mean “cannot go,” it more broadly means “not good,” “not acceptable,” or “won’t do.” The なければ (nakereba) part means “if (one) does not do [verb]…”. So, literally, 「V + なければ + いけません」 means “If [verb] is not done, it is not acceptable/it won’t do.” This logical consequence creates the meaning of obligation: “must do [verb]”.

In very informal, spoken Japanese, the いけません (or いけない) part is often shortened or dropped entirely. Common casual forms include:

• ～ないと (naito): Short for ～ないといけない/～ないとだめ. Ex: 宿題しないと。(Shukudai shinaito. – Gotta do homework / (If I don’t) do homework (it’ll be bad).) These are very common in relaxed conversation.
• ～なきゃ (nakya): Often used alone. Ex: もう行かなきゃ！ (Mou ikanakya! – Gotta go now!)
• ～なくちゃ (nakucha): Similar to なきゃ. Ex: 早くしなくちゃ。(Hayaku shinakucha. – Gotta hurry.)

To express past obligation (“had to do”), you make the いけません part past tense: いけませんでした (ikemasen deshita).

• Polite: ～なければいけませんでした (nakereba ikemasen deshita). Ex: 「会議に出なければいけませんでした。」(Kaigi ni denakereba ikemasen deshita. – I had to attend the meeting.) You can also use 〜なくてはいけませんでした (nakute wa ikemasen deshita).
• Casual: Often expressed using the plain past いけなかった (ikenakatta) with casual forms like なきゃ or ないと. Ex: 「行かなきゃいけなかったんだ。」(Ikanakya ikenakatta n da. – (The thing is) I had to go.) or 「早く起きないといけなかった。」(Hayaku okinai to ikenakatta. – I had to wake up early.)