Marginal revenue
Marginal revenue (MR) is the additional revenue a firm receives from selling one more unit of output, calculated as the change in total revenue divided by the change in quantity sold, or in continuous terms, the derivative of the total revenue function with respect to quantity.[1][2] In economics, it serves as a critical concept for understanding firm behavior in various market structures, guiding decisions on output levels to maximize profits. Under perfect competition, where firms are price takers, marginal revenue equals the market price because selling an additional unit does not affect the price of the product.[3] In contrast, in monopoly or other imperfectly competitive markets, the downward-sloping demand curve means that selling more units requires lowering the price on all units sold, resulting in marginal revenue being less than the price.[3] This distinction highlights how market power influences revenue dynamics and pricing strategies. Firms across market structures use marginal revenue in profit maximization by producing up to the point where marginal revenue equals marginal cost (MR = MC), as this equates the additional revenue and cost of the last unit produced.[4] Beyond production decisions, marginal revenue analysis extends to resource allocation, such as in labor markets where marginal revenue product determines optimal input use.[5]Fundamentals
Definition
Marginal revenue (MR) is defined as the additional revenue generated by selling one more unit of a good or service. It is formally expressed as the change in total revenue (TR) divided by the change in quantity sold (ΔQ), or MR = ΔTR / ΔQ.[1] Total revenue represents the overall income from sales and is calculated as the product of the price per unit (P) and the quantity sold (Q), so TR = P × Q.[5] Marginal revenue captures the incremental effect of increasing output by one unit, reflecting how additional sales impact overall earnings, often accounting for potential price adjustments needed to sell more units.[6] In contrast, average revenue (AR) measures the revenue per unit sold and is computed as AR = TR / Q, which typically equals the price P in standard market conditions. This distinction highlights that while average revenue provides an overall average, marginal revenue focuses on the specific contribution of the next unit to total revenue.[7] The concept of marginal revenue emerged in neoclassical economics, particularly through the work of Alfred Marshall in his Principles of Economics (1890), where it formed a key part of analyzing firm behavior and resource allocation.[8]Calculation
Marginal revenue can be calculated in discrete or continuous terms, depending on whether output changes are treated as finite increments or infinitesimal variations. In the discrete case, marginal revenue for the nth unit, denoted MR_n, is computed as the change in total revenue divided by the change in quantity: MR_n = (TR_n - TR_{n-1}) / (Q_n - Q_{n-1}), where TR represents total revenue and Q is quantity sold. This approach approximates the additional revenue from selling one more unit, assuming quantity changes by one unit.[9] For continuous analysis, marginal revenue is the derivative of total revenue with respect to quantity: MR = dTR / dQ. When total revenue is expressed as TR = P(Q) \cdot Q, where P is the price as a function of quantity, the chain rule yields MR = P + Q (dP / dQ).[10] This formula highlights that under a downward-sloping demand curve (where dP / dQ < 0), marginal revenue is less than the price, as the second term is negative.[10] The calculation assumes either constant price per unit, in which case MR equals P for all units since additional sales do not affect price, or a downward-sloping demand curve, where selling more units requires lowering the price on all units, reducing MR below P.[11] To illustrate, consider a linear demand curve P = 100 - Q. Total revenue is TR = Q(100 - Q) = 100Q - Q^2. The marginal revenue function is then MR = 100 - 2Q.[10] The following table computes discrete values for the first few units:| Q | P | TR | MR |
|---|---|---|---|
| 0 | 100 | 0 | - |
| 1 | 99 | 99 | 99 |
| 2 | 98 | 196 | 97 |
| 3 | 97 | 291 | 95 |
| 4 | 96 | 384 | 93 |
| 5 | 95 | 475 | 91 |