this cannot be answered with a single number because many factors influence the net profit.
A way to approach it is to look at your average monthly costs and compare it to the average income. The costs can vary widely between trainers and can be fixed or contingent on whether or not you train a client. Examples of fixed costs are leases for space and the utilities that go with it, liability insurance and potentially costs for employees. Variable costs would be transportation if you train at clients’ homes. Another aspect of cost is the equipment you purchase to train. Even though this expense is a one-time deal, it still should be pro-rated.