Fuel predictions question.

Hello,I have SU1.1 and often notice that the fuel remaining predictions are often zero on the ground before the flight is underway. When airborne they start to compute, but shouldn't the FMC have some idea of the route fuel expected consumption prior to taxi? Am I misunderstanding the FMC? Oh yes, I am setting up all of the parameters fully and correctly as far as I know...Cheers.C130