Grammar JLPT Level N4 - Lesson 26

Structure of なければならない:

Verb［ない］ + なければ + ならない
Verb［ない］ + なきゃ + ならない

Details about なければならない:

Like なければいけない, なければならない 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 become', or more simply '(A) cannot not be done'.
To make this construction, the auxiliary verb ない will need to be conjugated with ば, creating なければ (if not). After this, ならない (to not become) will be added to the end.

仕事(しごと)はしなければならない。
I must do my work.
先輩(せんぱい)が部屋(へや)に入(はい)って来(き)たら立(た)って挨拶(あいさつ)をしなければならない。
If your senpai comes into the room, you must stand and greet them.

As we 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 ならない.

今日(きょう)も帰(かえ)りが遅(おそ)くなったら妻(つま)に怒(おこ)られるから、もうすぐ帰(かえ)らなきゃ。
My wife is going to scold me if I come home late today too, so I have to go home soon.
今日(きょう)は家事(かじ)をやらなきゃならないから出(で)かけられない。
I have to do some chores today, so I can't go out.

なければならない

Usage Notes for なければならない:

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).