Average Variable Cost vs Total Cost
Average Variable Cost and Total Cost are two Production & Costs concepts in AP Economics that students often mix up. Average Variable Cost is the variable cost per unit of output produced. Total Cost is the sum of all fixed and variable costs incurred by a firm in producing a given level of output. Here is how they compare side by side.
It is calculated by dividing total variable cost by quantity of output. Average variable cost typically declines at first due to increasing efficiency, then rises due to diminishing marginal returns.
It represents the full economic expense of production and is calculated by adding fixed costs and variable costs at each output level. Total cost starts at fixed cost when output is zero.
Average Variable Cost vs Total Cost: Which Number Answers Which Question
| Dimension | Average Variable Cost | Total Cost |
|---|---|---|
| What it counts | Only costs that move with output, divided by output | Every cost the firm incurs at that output |
| Formula | Total variable cost divided by quantity | Total fixed cost plus total variable cost |
| Treatment of rent and insurance | Left out entirely | Included in full |
| Shape as output rises | Falls, bottoms out, then rises | Rises throughout, never falls |
| The decision it settles | Operate or shut down for now | Profit or loss, once revenue is subtracted |
| Where it appears on a diagram | On the per-unit graph beside marginal cost | On the totals graph against total revenue |
| Reading on a cost table | Dollars per unit, such as $4 a loaf | Dollars, such as $1,400 for the week |
Fixed costs sit in one and not the other
Average variable cost is a per-unit figure and total cost is a lump sum, so the two answer different questions about the same firm. Take a bakery that produces 200 loaves in a week. It pays $600 in rent whatever it bakes, and $800 on flour, labor and power that week. Total cost is $1,400. Variable cost alone is $800, so average variable cost is $800 divided by 200, or $4 per loaf. Notice that the $600 of rent never touches AVC. Average total cost would be $1,400 divided by 200, or $7 per loaf, and the $3 gap between the two averages is the fixed cost spread across output. Because the marginal product of extra workers first rises and then falls, AVC moves in a U shape: it falls while extra workers add output quickly, then climbs once the kitchen gets crowded and each extra loaf needs overtime pay. Total cost never behaves that way. It goes up with every additional loaf and can only sit still if the extra unit is free, which nothing is. The other split worth holding onto is what each one leaves out. AVC ignores the rent completely, so two bakeries with identical ovens, identical staff and wildly different leases report the same AVC and very different total costs. If a landlord raises rent by $200 a week, total cost climbs by $200 at every output level while AVC does not move at all. That test tells you which measure a question is really about.
Which one settles the decision in front of you
The two costs sit in different decisions. Total cost answers whether the firm made money: subtract it from total revenue and the sign of the result is profit or loss. Average variable cost answers a narrower short-run question, whether to keep the doors open at all. If price covers AVC, every unit sold contributes something toward the rent that has already been committed, so operating loses less money than closing. If price sits below AVC, each sale deepens the loss and shutting down is the cheaper option. That threshold, price equal to minimum AVC, is why AVC gets its own curve on the standard short-run graph. Keep the timing straight too. Fixed cost is fixed only in the short run, so a firm looking at total cost over a longer horizon can drop the rent by not renewing the lease. In the long run there are no fixed costs left and the shutdown test disappears: the firm exits if price is below average total cost. Exam questions exploit this gap constantly. A stem that says price is $5, AVC is $4 and ATC is $9 describes a firm that should keep producing this month while still losing money, because $1 per unit is going toward fixed costs that would otherwise be a complete loss. See /glossary/average-variable-cost for the curve on its own.
Frequently asked questions
Is average variable cost part of total cost?
Not directly, because AVC is a rate rather than a dollar amount. Multiply it by quantity first. AVC times output gives total variable cost, and total variable cost plus total fixed cost gives total cost. If AVC is $4 at 200 units, variable cost is $800, and adding $600 of fixed cost brings total cost to $1,400.
Why does the total cost curve start above zero?
Because fixed costs are owed even at zero output. Rent, insurance and loan payments do not disappear on a day the plant sits idle, so the total cost curve begins at the level of total fixed cost and rises from there. Total variable cost is the curve that begins at the origin, since a firm producing nothing buys no inputs.
Can average variable cost fall while total cost is rising?
Yes, and it normally does over the early range of output. Total cost rises with every unit produced because each unit consumes inputs. AVC divides variable cost by a growing quantity, so while extra workers are still adding a lot of output per hire, the per-unit figure drops. AVC turns upward only once diminishing returns set in.
Live Production Costs graph. Drag the curves, or open the full version.
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