なくてはいけないnakute wa ikenai“must do; need to do”

なくてはいけない means “must” or “have to”. Japanese has no single word for “must”, so it builds one from a double negative: “if you don’t do it, it’s no good”. 毎日勉強しなくてはいけません is “I have to study every day.” It is JLPT N5 grammar, and once you can take it apart, the related forms なければならない, ないといけない and なきゃ become easy to recognize.

なくては (if not doing) + いけない (no good) = must. Two negatives make one obligation.

What does なくてはいけない mean?

Split the pattern into its parts:

• 行かなくて — not going (negative て-form)
• は — topic / condition: “as for not going…”
• いけない — is no good, won’t do

So 行かなくてはいけない means “Not going won’t do”, which English says as “I have to go.” The polite ending is なくてはいけません.

The obligation can come from different places:

• Rules: ここでは靴を脱がなくてはいけません。 — You have to take off your shoes here.
• Schedules: 九時までに帰らなくてはいけない。 — I have to be home by nine.
• Your own sense of duty: もっと練習しなくてはいけない。 — I need to practice more.

In every case, the speaker says that skipping the action is not an option.

How to form なくてはいけない

Start from the ない-form, drop the final い, and add くてはいけない.

Every verb group follows the same path:

• う-verb: 書く → 書かない → 書かなくてはいけない
• う-verb: 払う → 払わない → 払わなくてはいけない
• る-verb: 起きる → 起きない → 起きなくてはいけない
• する: しない → しなくてはいけない
• 来る: 来ない (こない) → 来なくてはいけない

Changing the ending:

• Polite: 書かなくてはいけません
• Past (“had to”): 書かなくてはいけなかった／いけませんでした
• Question (“Do I have to…?”): 書かなくてはいけませんか

Casual speech squeezes the pattern. なくては becomes なくちゃ, and いけない is often dropped: 行かなくちゃ (“Gotta go”). You will also hear なきゃ, from the related なければ.

When is なくてはいけない used?

Explaining rules. Teachers, staff and signs use it for requirements: この紙に名前を書かなくてはいけません.

Talking about your own schedule. When you have to leave, go to work or finish something: 明日は早く起きなくてはいけない. This is often the reason for declining an invitation.

Personal resolutions. Telling yourself what you need to do: 野菜をもっと食べなくてはいけない (“I need to eat more vegetables”).

Asking about requirements. In polite speech, 〜なくてはいけませんか checks whether something is required: 予約しなくてはいけませんか (“Do I need a reservation?”).

Register. なくてはいけません works in polite conversation. In casual talk, most people switch to なくちゃ or なきゃ, because the full form is long. In formal writing and official rules, なければならない is more common.

なくてはいけない example sentences

The fourth sentence adds んです, which turns the obligation into an explanation: “the thing is, I have to go home”. That is how Japanese speakers politely excuse themselves.

Nuance of なくてはいけない

いけない vs ならない. The textbook pair なくてはいけない and なくてはならない mean the same thing. いけない leans toward the speaker’s own judgment or a specific situation (“I need to…”, “you’d better…”). ならない leans toward general rules and duties, and sounds more formal and written. In everyday conversation, いけない is the one you will hear.

Telling others what to do can sound bossy. 早く寝なくてはいけませんよ is fine from a parent or a doctor. From a junior to a senior, it sounds like a lecture. With people above you, use a request (〜てください) or give the information neutrally.

A “must” question expects “don’t have to” as the no answer. If someone asks 書かなくてはいけませんか, the answer “No, you don’t have to” is いいえ、書かなくてもいいです. Not いいえ、書かなくてはいけません, which would mean “No, you must write it.”

💡 Recognition tip: なくては, なくちゃ, なければ, なきゃ and ないと all start with ない. When you hear one of them followed by いけない, ならない, or nothing at all, think "must".

なくてはいけない vs てはいけない

These two differ by only a few sounds, and they mean opposite things.

Listen for the な: 書かなくては = must write, 書いては = must not write. When you read, check whether there is a ない stem before くては. See てはいけない for the prohibition pattern.

Common mistakes with なくてはいけない

Is なくてはいけない on the JLPT?

A typical listening task: a teacher tells students what to bring tomorrow, and you choose the picture of what they have to bring. Watch for the contrast between 〜なくてはいけません (must bring) and 〜なくてもいいです (don’t need to bring) in the same dialogue.

Practice questions for なくてはいけない

Learning path for なくてはいけない

Related grammar to review next

• てはいけない — the prohibition that sounds almost the same but means “must not”
• なくてもいい — “don’t have to”, the natural answer when something is not required
• なくちゃ — the casual contraction of なくては you will hear most in conversation
• なくてはならない — the same obligation with a more formal, rule-based tone
• ないといけない — a common spoken alternative with the same meaning

Learn なくてはいけない with Hane

Hane has you switch between なくてはいけない, てはいけない and なくてもいい in quick drills, so “must”, “must not” and “don’t have to” stop blurring together. Start practicing with Hane.