Economists recognize three distinct stages of production, which are defined by a concept known as the law of diminishing marginal returns. This law holds that as you add more workers to the production process, output will increase, but the size of that increase will get smaller with each worker you add. At some point, if you keep adding workers, your output may even start shrinking. The idea of the three stages of production helps companies set production schedules and make staffing decisions.

## Product Curves

There are three main product curves in economic production: the total product curve, the average product curve and the marginal product curve. The total product curve is a reflection of the firm’s overall production and is the basis of the two other curves. The average product curve is the quantity of the total output produced per unit of a "variable input," such as hours of labor. The marginal product curve is slightly different: It measures the change in product output per unit of variable input. For example, if the average curve depicts the number of units produced based on an overall number of employees, the marginal curve would show the number of additional units produced if one more employee is added.

## Stage One

Stage one is the period of most growth in a company's production. In this period, each additional variable input will produce more products. This signifies an increasing marginal return; the investment on the variable input outweighs the cost of producing an additional product at an increasing rate. As an example, if one employee produces five cans by himself, two employees may produce 15 cans between the two of them. All three curves are increasing and positive in this stage.

## Stage Two

Stage two is the period where marginal returns start to decrease. Each additional variable input will still produce additional units but at a decreasing rate. This is because of the law of diminishing returns: Output steadily decreases on each additional unit of variable input, holding all other inputs fixed. For example, if a previous employee added nine more cans to production, the next employee may only add eight more cans to production. The total product curve is still rising in this stage, while the average and marginal curves both start to drop.

## Stage Three

In stage three, marginal returns start to turn negative. Adding more variable inputs becomes counterproductive; an additional source of labor will lessen overall production. For example, hiring an additional employee to produce cans will actually result in fewer cans produced overall. This may be due to factors such as labor capacity and efficiency limitations. In this stage, the total product curve starts to trend down, the average product curve continues its descent and the marginal curve becomes negative.