be dollars to doughnuts that (something happens)
To be assured or certain to happen. The idea is that one is so confident in a particular outcome that they would bet money against something less valuable. It's dollars to donuts that Kevin will be late tonight—he's never on time.
be dollars to doughnuts that
be a certainty that. North American informal 1936 James Curtis The Gilt Kid If he were seen it was dollars to doughnuts that he would be arrested.