Each agricultural producer is always faced with the problem of how long complex agricultural equipment should be used, when it will be the need to buy a new one, or in general, when the need is to switch to a new direction. Complex agricultural machinery is expensive, maintenance and repairs of it are expensive as well, and our market economy is unpredictable. The solution to this problem is considered on the example of winter wheat harvesting with a self-propelled fourth-class combine harvester. The following theoretical prerequisite for solving the abovementioned problem is proposed. An agricultural producer purchased a combine harvester for 5 million rubles, and then the costs associated with its operation are summed up over the years: for fuels and lubricants, wages for machine operators, costs for repair and maintenance of the combine, costs for spare parts, cultivation and grain harvesting, taxes, etc. After the fifth year of operation already, according to the instructions, the combine harvester requires overhaul, and the costs of repair and maintenance are growing over time. The profit of an agricultural producer is formed as the difference between costs of the sale of grain. Over time, the productivity of the combine harvester decreases and at some point the operation of the combine becomes unprofitable; this is the point of obsolescence of the machine, when the agricultural producer must decide either to buy a new harvester or to change his business.