Originally Posted by
cordelli
How far in advance can I prepay my checked baggage fees?
You may prepay the service fee for your checked baggage within 24 hours of your flight departure. You may prepay this service fee online EasyCheck-in Online or at an EasyCheck-in kiosk at the airport.
So other than online or the kiosk within 24 hours, the answer is no.
Curious question: I checked in for my flight tomorrow, but when I got to the point where it asked me if I had any bags to check, I selected one, but it said it was no charge?

(I don't have status on United/CO).