off the top of your head INFORMAL Meaning: If you give som | Idioms & Phrases

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.

For example:

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.