How Long and For How Long?

[Alexander]

What is difference between How Long and For How Long?

Thanks in advance

[Bridget]

What is difference between How Long and For How Long?

Thanks in advance

When used to talk about duration, there's no difference. It's just that the preposition is at one end or the other, or can be omitted when in the final place of the sentence.

How long have you been waiting (for)?
For how long have you been waiting? (Often seen as formal)