Is "Needn't have to" correct? If not, what is?

American English (NY) here - i believe it’s grammatically correct but sounds super duper archaic. This could be a difference between British and American, but I can’t say for certain.

I agree. "She needn't sit" would be better.

I'm American and this is hurting my brain too. I think the sentence is actually present tense, and I would say "She shouldn't have to sit in the strange smelling bus..." If you really want to use "needn't", then "She needn't sit in the strange smelling bus..." But I don't know what a Brit would say here.

Sounds normal to me as a Brit. It means "need not". E.g. "You needn't come later" meaning "You do not need to come later".

Canada here. Its fine, but redundant. "She needn't sit..." is perfectly valid, and "need to" & "have to" are mostly interchangeable, so you *needn't* use both.

‘Needn’t have to’ doesn’t sound right, it feels very redundant. You could say “she needn’t sit in the strange smelling…” this sounds quite formal and old fashioned, it would be a lot more common to say “she doesn’t need to” or “she shouldn’t have to” in most cases. Needn’t (need not) is effectively interchangeable with ‘don’t need to’ or ‘shouldn’t have’ ‘You needn’t have bought me a gift’ ‘You needn’t attend the meeting, it is optional’ By old fashioned, I don’t mean that ‘needn’t’ is no longer used, but its uses in general English are more limited to formal situations. I use needn’t sometimes though as I like the sound of it.

1. It sounds a bit odd in this use. The most common way to use it with 'have' would be in a perfect tense sentence E.g. 'You needn't have done that' (You didn't need to have done that; that was kind of you). If the sentence is meant to be saying something like 'She shouldn't have to...' - expressing that "currently, she is being made to (or might be made to) sit in the bus, but I find that wrong", then I guess it works. But if it's just trying to say that she it's not necessary for her to sit in the bus, then the 'have to' is a bit redundant. \[As you probably know you can also use it without 'have', to indicate a lack of obligation. It can be a polite way of telling someone to not do something - notoriously job adverts would discriminate by saying e.g. 'Women need not apply'. Basically: Don't apply, we won't hire you\] 2. Even if used correctly, it is quite formal. I associate it as being something relatively posh older people (70+) might say. Otherwise, it's something that you might find in formal text like a form or something. It's definitely not the most natural way of expressing either sentiment above

Needn't valid if rare (or possibly British). It means "does not need to", but I don't think I've ever heard it used with "have to" after it before. That seems redundant.

To me it does indeed seem redundant to have both need and have serving the same purpose.

I'm American so I'm guessing but wouldn't it make more sense as needn't sit or needn't have sat? 

He need not have asked, but could/should have just done

It's correct but sounds odd or old fashioned to my American ear

Looks a bit off to me (British speaker). I would be more likely to use “needn’t” in the following way: “You needn’t do that”, as in “you don’t need to do that”. I personally agree it makes the “have to” redundant here, “she needn’t sit in the strange smelling bus” reads a lot better to me.

It doesn't sound right to me. I would probably say "She doesn't need to".

Fine by me in the Northeastern US, though as counterintuitive as it sounds, “I don’t need to” or “you don’t need to” etc. is heard as less formal.

I would say, “She needn’t sit…”, “she need not sit…“ or “she shouldn’t need to sit…”. The sentence as given feels awkward.

It’s fine, but not many native speakers will speak like this anymore. It’s quite old-fashioned and needn’t is commonly heard now.

The to is grammatically unnecessary but doesn't impact meaning. Needn't've is enough.

By itself it sounds redundant. You’d almost never say that. She needn’t sit in the bus, or she shouldn’t have to sit in the bus. But in this particular case, it is technically correct. It takes the place of shouldn’t in “she shouldn’t have to sit in the bus.” So there’s nothing technically wrong, it’s just weird.

Nobody says that in America. I don't have to. 99% of the time.

It’s incorrect because it’s redundant. It would be like saying “I don’t need to have to go to work” Idk why people are saying it’s correct

I think you'd say "She needn't have sat"

To me as a Brit the way to make this make the most sense would be to say “She Needn’t have *had* to sit on the smelly bus” I.e. this happened in the past, and she could have chosen to do something else, but she ended up sitting on the smelly bus anyway. To me this sentence structure further implies that she likely didn’t know she had a choice at the time.

Without further context, it's impossible to be sure of the intended meaning. However, my best paraphrase would be: "there's no reason that she should have to sit...". The two verbs "need (not)" and "have to" are being used to describe different types/layers of necessity: there's a layer of compulsion thought to be acting on the girl ("have to sit...") that is or would be unnecessary ("needn't") in the opinion of the speaker. In the negative, "need not" can behave like a modal verb such as *must* or *can*: it does not inflect for person and it takes a bare infinitive in its complement.

As a Brit, I think its a little off. I would expect to hear, "She **needn't have taken** the bus after school", meaning it was unnecessary for her to have taken the bus, maybe because someone would have picked her up from school instead.

Have to is indeed redundant. In addition, you sit on a bus, not in.

An American would probably say “You don't need to” or “You don’t have to ....”

It’s redundant. “She needn’t sit in the etc.” “Needn’t”=“need not” which means “doesn’t have to” or “doesn’t need to.”