off the top of (one's) head (adjectival) In an impromptu way: impromptu = 即兴 I don't know off the top of my head. = I can't think of it right now.

Yes. This idiom means to speak from recollection or to recall something without preparation. Examples: 1. He didn't prepare for the meeting, he just spoke off the top of his head. 2. I can't remember all those dates off the top of my head, so I'll need to check the documentation and get back to you.