# Costs

## Vocabulary

### average cost

cost per unit of output

### average fixed cost (AFC)

fixed cost divided by the quantity of output
$AFC=\frac{FC}Q$

### average total cost (ATC)

total cost divided by the quantity of output; the sum of average fixed and average variable costs
$ATC\;=\;\frac{TC}Q$
$ATC\;=\;AFC\;+\;AVC$

### average variable cost (AVC)

variable cost divided by the quantity of output
$AVC\;=\;\frac{VC}Q$

### constant returns to scale

occurs when long-run average total cost remains the same as output increases

### diseconomies of scale

occurs when long-run average total cost rises as output rises

### economic cost

the sum of explicit and implicit (opportunity) costs

### economies of scale

occurs when long-run average total cost falls as output rises

### explicit cost

a cost involving monetary payment

### fixed cost (FC)

the cost of fixed inputs; does not change as output changes

### implicit cost

a cost that does not require the buyer to pay cash, or that cannot easily be assigned a monetary value

### law of diminishing marginal returns

the observation in the short run that each additional unit of a production input, holding all other inputs fixed, will yield progressively smaller increases in output

### long-run average total cost (LATC)

the minimum per-unit cost of producing any level of output when all inputs are variable

### long-run total cost

the minimum cost of producing any level of output when all inputs are variable

### marginal cost (MC)

the additional cost that a firm incurs by producing an additional unit of output, which must be covered in order to remain operational in the short run
$MC\;=\;\frac{\triangle TC}{\triangle Q}$

### short run

the period in which at least one productive input is fixed

### total cost (TC)

the sum of a firm's fixed and variable costs

### variable cost (VC)

the cost of variable inputs; changes as output changes