It has been 20 yrs but:
8/10ths of sweet FA.
The fuel calculation for the flight will be done on distance to be flown, diversions, weather etc etc. This results in an APS weight. The remaining weight up to MTOW (or whatever other limit is involved) is available for load (pax/freight)
All that said, the bean counters in commercial aviation often use a 3% figure (not standardized, this) for the cost of hauling fuel that will not be burned.
This takes into account slower take off, longer to cruise etc. Or so they say. Think of a truck with 20 MT on board. It will burn x amount of fuel on a run. Add 5 tons and it will burn a bit more for hills, moving off etc.
Using this:
2.5 MT = 5500 lbs
3% = 165 lbs