Summary of Costs of Production in Microeconomics

## Introduction This study material explains how economists measure the costs firms face when producing goods and services. Understanding cost concepts is essential for analyzing firm decisions about output, pricing, entry, and exit. ## What are costs? Firms incur costs to produce output. Economists define cost broadly as the opportunity cost of all resources used in production. Costs determine profit and therefore influence a firm's decisions. > Definition: Profit = Total revenue - Total cost ### Total revenue - Total revenue = price × quantity sold. - Example: If a firm sells 10,000 cookies at $2 each, total revenue = $20{,}000. ### Total cost and opportunity cost - Economists include both explicit and implicit costs when measuring total cost. - Explicit costs: monetary payments the firm makes (wages, rent, materials). - Implicit costs: value of resources owned by the firm for which no cash payment is made (forgone wages, forgone interest on savings). > Definition: Opportunity cost = what you give up to get something; includes explicit and implicit costs Fun fact: Firms that ignore implicit costs risk overestimating profitability and making poor long-run decisions. ## Fixed and variable costs - **Fixed costs** do not vary with output (e.g., rent, salaried bookkeeper). These are incurred even if output is zero. - **Variable costs** change with output (e.g., raw materials, hourly labor). > Definition: Total cost = Fixed cost + Variable cost Table: Fixed vs Variable Costs | Feature | Fixed Cost | Variable Cost | | --- | ---: | ---: | | Changes with output? | No | Yes | | Example items | Rent, depreciation, some salaries | Materials, hourly wages, packaging | | At zero output | Still incurred | Zero | Example: Conrad's Coffee Shop has a fixed cost of $3.00 per hour and variable costs that rise with cups produced. ## Average and marginal cost To guide production decisions, firms use average and marginal cost measures. > Definition: Average total cost (ATC) = Total cost ÷ Quantity = $\text{ATC} = \dfrac{TC}{Q}$ > Definition: Average fixed cost (AFC) = Fixed cost ÷ Quantity = $\text{AFC} = \dfrac{FC}{Q}$ > Definition: Average variable cost (AVC) = Variable cost ÷ Quantity = $\text{AVC} = \dfrac{VC}{Q}$ > Definition: Marginal cost (MC) = Increase in total cost from producing one more unit = $\text{MC} = \Delta TC$ when $\Delta Q = 1$ Notes: - ATC = AFC + AVC. - AFC falls as output rises because fixed cost is spread over more units. - MC typically rises with output due to diminishing marginal product of inputs. Practical example (summary from Conrad's data): - If TC at 2 cups is $3.80, ATC at 2 = $\dfrac{3.80}{2} = 1.90$. - If TC at 2 is $3.80 and TC at 3 is $4.50, MC of the 3rd cup = $4.50 - 3.80 = 0.70$. Did you know that marginal cost often intersects average total cost at ATC's minimum? This property helps determine efficient scale. ## Economic vs accounting profit - **Accounting profit** = Total revenue - Explicit costs. - **Economic profit** = Total revenue - (Explicit + Implicit costs). > Definition: Economic profit accounts for all opportunity costs; accounting profit ignores implicit costs Implications: - Accounting profit > Economic profit (unless implicit costs are zero). - A positive economic profit signals that a firm covers all opportunity costs and earns a surplus reward for owners. - Negative economic profit (economic loss) means the firm fails to cover opportunity costs and may exit the industry in the long run. Example: If Caroline could have earned $15{,}000 working elsewhere (implicit cost) and the business shows $20{,}000 revenue with $8{,}000 explicit costs, then accounting profit = $12{,}000 but economic profit = $12{,}000 - $15{,}000 = -$3{,}000. Fun fact: Banks' interest payments are explicit costs, but the forgone interest on personal savings used to finance a business is an implicit cost. ## Relationship between production function and cost curves - Diminishing marginal product: as