In the short run, firms can make super-normal profits or losses under perfect competition. The firm has fixed resources and maximizes profit or minimizes loss by adjusting output. When a firm operates in a perfectly competitive market, its supply curve is its short-run marginal cost curve above average variable cost. The firm should not produce, but should shut down in the short run if its loss exceeds its fixed costs. By shutting down, its loss will just equal those fixed costs. The shut down point is the level of output and price at which the firm just covers its total variable cost. For perfect competition, marginal revenue is equal to price as the firm is facing a perfectly elastic demand.
Entry and exit is possible in the long run of perfect competitive. Long run firms are attracted into the industry if the supernormal profits are making by the