It is important to understand how the concept to relevant cost can be incorporated into the analysis of short-run cost. Suppose a firm is currently producing 6 units of output per period and is considering increasing this amount to 7. In deciding whether to produce the seventh unit of output, the relevant cost is the marginal cost In other words, it is the change in total cost itself that must be considered. This is because whether the firm produces 6 or 7 units of output per time period, it still must pay the same amount of fixed cost. By evaluating the change in total cost, the firm automatically excludes fixed cost from consideration.