A profit maximizing perfectly competitive firm should produce where P = MC. Considering the data to the left, the alert student might notice that, as far as this firm is concerned, it doesn't matter if it produces 12 or 13 units; profits will be the same. The 13^th unit adds zero to profit.

   It would be just as correct to say that a profit maximizing firm will either produce where P = MC, or it will come as close as possible without expanding to a level of output at which P < MC. For simplicity, as long as a level of output is available at which P = MC, we will assume that this is the output chosen by the firm. Therefore, for the firm whose data is shown to the left, profit maximizing output is 13.