Any … at all: bất cứ / bất kỳ

Bất cứ and bất kỳ mean "any … at all". Put either one in front of a question word or a noun: bất cứ ai (anyone at all), bất cứ lúc nào (any time), bất kỳ ngày nào (any day). They mean the same; bất cứ is the one you'll hear more in speech, and bất kỳ (also spelled bất kì) is common in writing.

In a statement, cũng goes before the verb, just as in ai cũng (everyone) and lúc nào cũng (always), which you know. Bất cứ makes them sound complete, "any one at all, without exception": Bất cứ ai cũng làm được. Anyone can do it. In relaxed talk the plain question word is often enough: Anh gọi em lúc nào cũng được.

In nếu (if) sentences, offers and notices, there's no cũng: Nếu chị cần bất cứ gì, cứ nói em nha. If you need anything at all, just tell me. At the end of emails and notices you'll see the written formula Nếu có bất kỳ thắc mắc nào, xin vui lòng liên hệ, if you have any questions, please get in touch.