I once saw a sentence reading "When are you open until?" which made enough sense to me to understand it. Later, I tried to come up with sentences having a similar structure; but, no matter what sentences I came up with, they all sounded weird. Here's one:

"When are you going to school until?" (I'd appreciate it if you'd let me know if this is correct)

I was wondering whether there was a grammatical rule for these kinds of sentences.


The idiomatic form is

Until when are you open?

Just because people can figure out what is intended by something like "When are you open until" does not make it idiomatic. Moreover, you can avoid the whole issue by asking

When are you open?

which invites an answer of when do you open and when do you close. Furthermore, you can ask only about closing time with

When do you close?

In short, you do not end a question with the preposition "until," and there are few if any cases where you must use the locution "until when" in a question.

  • maybe it's a localised thing but I've heard and used 'when [are] you open till?' in speech – Smock Jun 17 '19 at 15:29

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