Every commercial jet has a range within which the CofG must be located after
all the effects of basic weight, pax, cargo and fuel have been considered.
When that CofG has been calculated by the use of either a computerized program, or manually with a proforma that has a series of steps of filling in the squares and adding all the weights, the end result of which will give you a Zero Fuel Weight (the weight of everything except the fuel), and adding the total fuel will give you the gross weight, and minus the taxiing fuel will give you takeoff weight.
So, together with many other factors (temp, OAT, runway length, etc), the pilots figure out their takeoff performance numbers (like V1, Vr and V2) using this takeoff weight calculated figure.
In addition, because the calculated CofG can be within a range of percent MAC (mean aerodynamic chord), the pilots simply use the adjustable pitch trim to account for where the actual CofG is located.
For a forward CofG, the pitch trim is adjusted slightly nose up, and vice versa.
This allows for predictable pitch control at the point of liftoff, it's up to the pilot to retrim as usual from then on!
That's the idea anyway!
