off the top of one's head

• off the top of one's dome

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off the top of one's head

1. (idiomatic) In an extemporaneous manner; without careful thought, preparation, or investigation.

   Synonyms: offhandedly, on the spot

   I cannot think of any good examples off the top of my head, but give me a couple of hours and I'm sure I could come up with something.

   • 1990, Ronald Inglehart, Culture Shift in Advanced Industrial Society, Princeton University Press, →ISBN, page 130:

     Ideally, one would wish to explore them through a series of depth interviews extending over several months, rather than by a brief survey interview, which necessarily tends to elicit responses off the top of one's head.

   • 2004, Christopher Peterson, Martin E. P. Seligman, Character Strengths and Virtues: A Handbook and Classification, Oxford University Press, →ISBN, page 633:

     These responses are not analyzed but are intended to discourage answers off the top of one's head to the next question, which explicitly asks if these situated responses reflect the strength of character on focus.

   • 2008, Christine Son, Off the Menu, Penguin, →ISBN:

     “Oh, I don't have my stuff with me, and I don't know her work phone number off the top of my head. Here, take one of my cards.” “Are you a lawyer, too?” he asked, and then perused her information.

2. Used other than figuratively or idiomatically: see off,‎ top,‎ head.

• Usually used to characterize the manner of one's thinking or speaking.
• Often indicates a random piece of information put forth by a knowledgeable expert in the topic spoken within.

• extemporize

• “off the top of one's head”, in Lexico, Dictionary.com; Oxford University Press, 2019–2022.
• “off the top of your head”, in Cambridge English Dictionary, Cambridge, Cambridgeshire: Cambridge University Press, 1999–present.
• “off the top of your head” in Longman Dictionary of Contemporary English, Longman.
• “off the top of one's head”, in Collins English Dictionary.