Short-Run Costs and Output Decisions

Overview

In the short run, firms must make key decisions about production and resource allocation. These decisions are shaped by market conditions, available technology, and input prices.

• Output Decision: How much output to supply to the market.

• Production Technique: How to produce the chosen output (selection of technology or method).

• Input Demand: How much of each input to employ.

These decisions depend on:

• Output price (affects supply decisions)

• Available production techniques (affect production method)

• Input prices (determine input demand)

Costs of Production

Production costs are central to firm decision-making and market supply.

• Explicit costs: Direct, out-of-pocket payments for inputs.

• Implicit costs: Opportunity costs, including normal returns on capital.

• Costs depend on quantities and combinations of inputs used.

• Costs form the basis of the supply curve in output markets.

Firms acquire inputs from:

• Output markets: For goods and services prices.

• Input markets: For labor, capital, and materials prices.

The Short Run

The short run is defined by the presence of at least one fixed factor of production. Firms face constraints in adjusting all inputs.

• At least one input is fixed (cannot be changed quickly).

• Firms cannot freely enter or exit the industry.

• Fixed costs must be paid regardless of output level.

• In the long run, all inputs become variable; there are no fixed costs.

Types of Costs

1. Fixed Costs (FC)

Fixed costs do not change with output in the short run and must be paid even if output is zero.

• Examples: Rent, insurance, machinery depreciation, salaries of permanent staff.

• Represent unavoidable costs.

• Firms have no control over fixed costs in the short run.

Formula:

• Total Fixed Cost (TFC): Overhead expenses paid regardless of output.

• Capital: Often has both fixed and variable components.

2. Average Fixed Cost (AFC)

Average fixed cost is the fixed cost per unit of output.

• AFC curves are downward sloping and never reach zero.

• Spreading fixed costs over more units reduces AFC.

3. Variable Costs (VC)

Variable costs change with the level of output and depend on production activity and input prices.

• Examples: Wages, raw materials, utilities.

• Depend on input requirements and prices.

Total Variable Cost (TVC):

• At any output level, TVC depends on available production techniques and input prices.

• Some capital (e.g., rented equipment) can be varied in the short run.

The Total Variable Cost Curve

The TVC curve shows the relationship between total variable cost and output.

• Graphically, the slope of TVC is the Marginal Cost (MC).

Marginal Cost (MC)

Marginal cost is the increase in total cost from producing one more unit of output.

• or

• MC reflects changes in variable costs only.

• MC correlates inversely with the marginal productivity of labor (MP_L):

Relationship Between Productivity and Cost

Productivity and cost are closely linked in production decisions.

• Efficient input use (high productivity) minimizes MC.

• Diminishing returns reduce productivity, increasing MC.

• Rising MC reflects the law of diminishing returns.

Diminishing Returns and Marginal Cost

As more variable inputs are added to fixed resources, each additional unit contributes less output, raising MC.

• Marginal product (MP) rises, peaks, and then declines.

• MC curve rises sharply as diminishing returns set in.

Total Variable Cost and Marginal Cost

The relationship between TVC and MC is fundamental to cost analysis.

• As TVC increases, its slope (MC) rises.

• Diminishing returns cause the TVC curve to steepen at higher output levels.

• The slope of the TVC curve () equals MC.

Average Variable Cost (AVC)

AVC is the variable cost per unit of output.

• AVC follows the shape of MC but lags behind.

• MC intersects AVC at AVC's minimum point:

  • When , AVC is falling.

  • When , AVC is rising.

• AVC curve is typically U-shaped.

Total and Average Costs Relationship

Total cost is the sum of fixed and variable costs. Average total cost (ATC) is the total cost per unit of output.

• TFC is a horizontal line (unchanged by output).

• As output rises, ATC gets closer to AVC but never meets it.

Cost Curve Behavior

Cost curves illustrate how costs change as output varies.

• ATC follows MC but lags slightly.

• The minimum point of ATC lies to the right of AVC's minimum.

• ATC decreases initially (as fixed costs spread) and rises later (as variable costs increase).

• When ATC is not minimized, it declines rapidly at first because fixed costs are spread over more output.

Key Takeaways

• All short-run cost curves (MC, AVC, ATC) are U-shaped due to diminishing returns.

• Accounting costs = explicit, out-of-pocket expenses.

• Economic costs = explicit + opportunity costs.

• Cost curves summarize how efficiently a firm produces output given its technology and resource constraints.

Summary Table: Cost Concepts