before you know it

before you know it

Quickly or suddenly. I'm not far from your house, so I'll be there before you know it. Before you know it, you'll be graduating, so start thinking about your future now.
See also: before, know
Farlex Dictionary of Idioms.

before you know it

almost immediately. I'll be there before you know it. If you keep spending money like that, you'll be broke before you know it.
See also: before, know
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.

before you know it

see under before you can say Jack Robinson.
See also: before, know
The American Heritage® Dictionary of Idioms by Christine Ammer.
See also:
  • before you know where you are
  • as we know it
  • as you know
  • AFAIK
  • I know
  • by any chance
  • closed book, a
  • a closed book
  • (I) can't say as I do
  • can't say as I do