Horses can carry between 12% and 20% of their body weight, but body weight is not the only factor that decides if it is justified to carry a certain amount of weight. You have to look at the muscles, build and breed of the horse in order to make a safe observation and conclusion.
Is the back weak or strong? Does the horse have enough muscle? Also, you need to check the body shape of the person who is going to ride the horse. For example, if a person is very overweight the pressure on the horse’s back is much higher than with a person with the same weight but a more muscular build. Because fat is loose tissue, the weight of the fat will generally cause more pressure on the horse’s back at a later stage than with ‘normal’ body weight. In this way, the horse gets ‘two beats’ of weight per stride.
Horse riding is a sport in which you are dealing with both yourself and another living creature. It is up to us to make sure that the horse does not have to carry someone who is not fit for it. There is no weight difference between what a horse should carry during leisure and competition. In order to ride competitions, you have to challenge not only your horse to perform at his best, but yourself as well. The only way to challenge yourself is to be as fit as your horse and to make sure that you are both working towards the same goal. The same applies for leisure: you want to enjoy the ride and the only way to do so is if your horse is enjoying it too.