Hello,

Trying to book flights to Vegas for April. One of the legs appears to be on a K-fare (another flight is $40 cheaper and a L fare). I've read you can upgrade with miles on a K-fare. But with K being the lowest bucket you can upgrade from i'm curious if thats even feasible (kind of how an FO can technically upgrade on an LGA->ATL flight but thats not going to actually happen).

Is it likey to be able to use miles to upgrade? If so, can i do this in advance? Or do I have to do it the day of at the gate? Any way to guess how many miles it would take?

I'd gladly save $40 on the L fare but if the odds are good that i'l be able to use 15k miles or so then i'd certainly go for it.

All feedback is appreciated. Thanks