V1 is an arbitrary number in most cases, set to save money and time in computing the takeoff limits. The minimum V1 would be to satisfy the case of continuing the takeoff, so that the airplane just reached screen height at the end of the takeoff distance (also limited by Vmcg). The maximum V1 would satisfy the case where the airplane rejected the takeoff and just stopped at the end of the emergency distance (also limited by Vr or V2).
The only time this is likely to give the same V1 is for a perfectly balanced field, something that rarely exists.
So it is possible to calculate a range of V1s for every takeoff and for the pilot to choose a figure somewhere in the middle, or, if she sees a reason to use the minimum (obstacles close in, poor runout surface, contamination etc) would choose the minimum V1 and for a longer runway or obstacles further out, or for considerations of wind shear, traffic etc would choose the Maximum V1.
In practice leaving this decision to pilots is hazardous, not to say contentious, so most companies use Boeing takeoff figures that use a standard V1/Vr ratio for the whole chart, or in the case of the CDU calculations, the entire program. Sure it is within the range, but is it the best speed to use?
You can figure the maximum V1 by looking at the speed appropriate for the runway for a takeoff at maximum TOW (up to the Vr speed for the current weight of course). If you are equal to or lighter than that, that V1 speed will work for you and will also cover the continued takeoff case. I hesitate to suggest an easy way to calculate the Min V1, but if a takeoff is acceptable when the runway is contaminated and the V1 is 20 knots or so below standard speeds, then it should also be OK when the runway is in good condition.