Grammar Info
N4 Lesson 9: 8/15

なければいけない
must do, have to do

Verb[ない]+と+いけない/ならない is also used to express duty or necessity.

Structure
Casual
Formal
Verb[ない] + ければ + いけない
Verb[ない] + きゃ + いけない
Verb[ない] + ければ + いけません
Verb[ない] + きゃ + いけません
Details
Register Formal
使用域 硬い
Information
Like なくてはいけない, なければいけない is a structure that implies that something ‘must be done’. However, it is important to remember that this is actually a double negative, and therefore means ‘If (A) is not done, it cannot go’, or more simply ‘(A) cannot not be done’.
To make this construction, the auxiliary verb ない will need to be conjugated with , creating なければ (if not). After this, いけない (to not be able to go) will be added to the end.
  • 来月(らいげつ)に友達(ともだち)結婚式(けっこんしき)に行(い)かなければいけない
    Next month, I have to go to my friend's wedding. (Not going to the wedding is not going to work)
  • 車(くるま)駐車場(ちゅうしゃじょう)に止(と)めなければいけない
    Cars have to be parked in parking lots. (Not being parked in a parking lot is unacceptable)
As learned in the なきゃ lesson, なければ may be shortened to なきゃ. This structure is frequently used either with or without the added いけない.
  • ここ話(はな)している場合(ばあい)じゃない。息子(むすこ)迎(むか)えに行(い)かなきゃ
    This is not the time to talk here, I have to go pick up my son.
  • 宿題(しゅくだい)、調(しら)べなきゃいけない事(こと)があるから、パソコン貸(か)し
    Since I need to look up something for my homework, would you please lend me your computer?
Caution
While いけない (to not be able to go) and ならない (to not become) are quite similar, ならない will rarely be used outside of formal situations, or in writing. Due to this, いけない will be heard much more frequently in speech (when it is not omitted).
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仕事(しごと)行(い)かなければいけない
I have to go to work.
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冬(ふゆ)になったら、暖房(だんぼう)つけなければいけません
When winter comes, I will have to turn on the heater.
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覚(おぼ)えにくいけど覚(おぼ)えなければいけません
It is difficult to remember, but I must (remember).
Play  
Books
Genki I 2nd Edition
Page 273
Tobira
Page 43
Tae Kim's Japanese Grammar Guide
Page 142