Using ダメ with なくては？


I read that しなくてはダメ means “to have to do something” but someone said ダメ cannot
be used with なくては to mean “have to”. I get different answers from different
sources, both being Japanese speakers. What is correct?




しなくちゃダメ、しないとダメ、しなくてはダメ are all used very frequently in Japanese, as a simple
Google search (with quotation marks) will quickly demonstrate. 駄目 itself is
often [considered somewhat informal](https://tap-biz.jp/lifestyle/word-
meaning/1052937) (compared to なりません, いけません etc）though, so maybe that's what
your other Japanese source was referring to.

