This means you 'must do' something. It shows something is necessary. It is a polite way to say this.
Verb [ない-form] + と + いけませんPrimary
This means you 'must do' something. It shows something is necessary. It is a polite way to say this.
そろそろ会議を始めないといけません。
We have to start the meeting soon.
昨日は図書館に本を返しに行かないといけませんでした。
I had to go return a book to the library yesterday.
健康のために、甘いものを食べ過ぎないようにしないといけません。
For the sake of my health, I must be careful not to eat too many sweets.
パスポートを更新しないといけなかったので、旅行の計画を延期しました。
I had to renew my passport, so I postponed my travel plans.
このアパートでは、ゴミは朝８時までに出さないといけません。
In this apartment building, you must take out the trash by 8 AM.
This phrase means you must do something. It is like a rule you have to follow. It is not about what you feel is right. It is about what the situation needs.
Both mean 'must do'. '〜なければなりません' is more formal. You see it in writing. '〜ないといけません' is common in daily talk. It is polite. It is the polite way to say '〜ないといけない'.
Use this when you need to say you "must do" something. This is a polite way to say it. You should use the full phrase. Do not make it shorter.
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