off the top of (one's) head

off the top of (one's) head

From memory or without much or careful consideration. A: "How much can we expect to earn this quarter?" B: "Off the top of my head, it should be around $200,000, but I'll have to check the figures when I get to the office." I know of two people who are coming off the top of my head, but I'm pretty sure more said they'd be here. John can list the capital cities of all 50 states off the top of his head.
See also: head, of, off, top
Farlex Dictionary of Idioms.

(right) off the top of one's head

Fig. without giving it too much thought or without precise knowledge. Mary: How much do you think this car would be worth on a trade? Fred: Well, right off the top of my head, I'd say about a thousand. Tom: What time does the morning train come in? Bill: Off the top of my head, I don't know.
See also: head, of, off, top
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.

off the top of one's head

In an impromptu way, without much thought, as in Off the top of my head I'd say we'll double our profits in a year. This idiom suggests one has not used the inside of one's head before making some statement. [Mid-1900s]
See also: head, of, off, top
The American Heritage® Dictionary of Idioms by Christine Ammer.

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
Collins COBUILD Idioms Dictionary, 3rd ed.

off the top of your head

without careful thought or investigation. informal
1988 Jamaica Kincaid A Small Place He apologises for the incredible mistake he has made in quoting you a price off the top of his head which is so vastly different (favouring him) from the one listed.
See also: head, of, off, top
Farlex Partner Idioms Dictionary

off the ˌtop of your ˈhead

(informal) as a guess; without having time to think carefully: Off the top of my head I’d say it would cost $2 000 to do the repairs. ‘What’s the population of Liverpool?’ ‘I’m afraid I couldn’t tell you off the top of my head.’
See also: head, of, off, top
Farlex Partner Idioms Dictionary

off the top of (one's) head

Informal
In an impromptu way: She recited the poem off the top of her head.
See also: head, of, off, top
American Heritage® Dictionary of the English Language, Fifth Edition.

off the top of one's head

Extemporaneously, impromptu; impetuously. A mid-twentieth-century Americanism, the term appeared in Harold L. Ickes’s Secret Diary (1939): “He was impetuous and inclined to think off the top of his head at times.” Author June Drummond (Junta, 1989) wrote: “‘And then, you just acted off the top of your head.’ Richard half-smiled. ‘You know I have that failing.’”
See also: head, of, off, top
The Dictionary of Clichés by Christine Ammer
See also:
  • on mature consideration
  • on mature reflection/consideration
  • be careful
  • if you can't be good, be careful
  • puzzle out
  • puzzle out (something)
  • snap decision
  • nut out
  • rubber stamp
  • snap judgment