off the top of your head

off the top of your head

If you say something off the top of your head, you say it without thinking about it much or without trying to check it or find out more facts about it. I can't remember off the top of my head the date of the wedding. I'm thinking off the top of my head here. OK, off the top of your head, do you know the capital of South Korea?
See also: head, of, off, top