なくてはいけない

expression

cannot do without; indispensable; absolutely necessary

Expresses that something is essential or that one cannot manage without it. Often used with a noun marked by が or は.

• この仕し事ごとには経けい験けんが無なくてはいけない。

  Experience is indispensable for this job.

• 生いきていくには水みずが無なくてはいけない。

  You cannot live without water.

expression

have to do; must do

Attaches to the negative stem of a verb (ない-form minus ない) to express obligation or necessity. Equivalent to なければならない but slightly more colloquial.

• 明日あしたまでにレポートを出ださなくてはいけない。

  I have to submit the report by tomorrow.

• もっと勉べん強きょうしなくてはいけない。

  I must study more.