Every horse is unique so the energy calculation will never be perfect for you and your horse. The energy calculation is based on how much your horse weight, the weight it has to carry, the speed during your trainings and what gait it is in.
You can use it as recommendation and it can give you a hint on your energy consumption and how they changes when you alter your training routines. If you want to read more about calculating your horse energy consumption we highly recommend Nutrition of the Exercising Horse by Markku T. Saastamoinen.