off the top of your head Informal
Meaning: If you give someone information off the top of your head, you do so from memory, without checking beforehand.
- I can't tell you Maxine's phone number off the top of my head. I'll have to check.
- I don't know for sure, but off the top of my head I'd say that renting a two-bedroom apartment would cost about a thousand dollars a week.
The one thing that everyone can tell you off the top of their head is