Average variable cost (AVC) is total variable cost divided by the quantity of output (AVC = TVC/Q). In AP Micro, it's the per-unit cost of inputs a firm can adjust in the short run, and it sets the shutdown threshold, since a firm shuts down when price falls below minimum AVC.
Average variable cost is exactly what it sounds like, the variable cost spread over each unit you produce. Take total variable cost (things like labor and raw materials that change with output) and divide by quantity. So if a bakery spends $200 on flour and wages to bake 100 loaves, AVC is $2 per loaf.
On a graph, AVC is U-shaped. It falls at first because of increasing marginal returns, then rises once diminishing marginal returns kick in and each extra worker adds less output. The marginal cost (MC) curve cuts through AVC at its minimum point, a fact AP loves to test. One more thing worth getting straight, because the thin textbook version often blurs it. AVC is fundamentally a short-run concept. Per EK PRD-1.A.9, in the long run all inputs are adjustable, so all costs become variable and the distinction between AVC and ATC disappears. That's why understanding AVC is the price of admission to long-run cost analysis in Topic 3.3.
AVC lives in Unit 3 (Production, Cost, and the Perfect Competition Model) and supports learning objectives AP Micro 3.3.A, 3.3.B, and 3.3.C, which ask you to define cost concepts, explain how production and cost connect in the short run versus the long run, and calculate cost measures from tables and graphs. The payoff comes fast. AVC powers the shutdown rule: a perfectly competitive firm keeps producing in the short run as long as price covers AVC, because it's at least paying its variable bills and chipping away at fixed costs. If price drops below minimum AVC, producing makes losses worse, so the firm shuts down. That single rule connects cost curves to firm behavior, market supply, and eventually long-run exit decisions, which makes AVC one of the most exam-relevant curves on the standard firm graph.
Keep studying AP Microeconomics Unit 3
Average Total Cost (Unit 3)
ATC = AVC + AFC, so the vertical gap between the ATC and AVC curves on any firm graph is exactly average fixed cost. The gap shrinks as output rises because fixed cost gets spread over more units. AVC sets the shutdown decision; ATC sets the profit and exit decisions.
Marginal Cost (Unit 3)
The MC curve always crosses AVC at AVC's minimum point. The logic is simple. If the cost of the next unit is below your current average, it pulls the average down; if it's above, it pulls the average up. AP graphs are wrong if MC doesn't pass through the bottom of the AVC curve.
Diminishing Marginal Returns (Unit 3)
Diminishing marginal returns explain why AVC is U-shaped. Once each added worker produces less than the one before, the variable cost per unit starts climbing. The shape of the AVC curve is the production function flipped into cost terms.
Long Run and Economies of Scale (Unit 3)
In the long run there's no fixed cost, so AVC and ATC merge into one long-run average total cost curve. Whether that LRATC falls, stays flat, or rises is what economies of scale, constant returns, and diseconomies of scale describe.
AVC shows up two ways. First, in calculations from a cost table, like the 2026 FRQ that gave a total cost schedule and asked for cost measures, where you find TVC by subtracting fixed cost from total cost and then divide by quantity. Second, on firm graphs, like the 2023 FRQ that handed you demand, MR, ATC, AVC, and MC curves for a profit-maximizing firm and expected you to read profit, loss, and the shutdown condition off of them. Multiple-choice questions test whether you know the shutdown rule (produce if P ≥ AVC in the short run), whether you can spot that MC crosses AVC at its minimum, and whether you understand that AVC is a short-run idea that collapses into LRATC once all inputs become variable. Be ready to both compute it from a table and locate it on a graph.
ATC includes fixed costs; AVC doesn't. That difference decides two different questions. Compare price to ATC to find profit or loss (and the long-run exit decision). Compare price to AVC to make the short-run shutdown decision. A firm with P below ATC but above AVC operates at a loss in the short run, because the revenue covers all variable costs plus some of the fixed costs it would owe anyway.
Average variable cost equals total variable cost divided by quantity (AVC = TVC/Q), and you can also find it as ATC minus AFC.
AVC is U-shaped because increasing marginal returns push it down at low output and diminishing marginal returns push it up at higher output.
The marginal cost curve always intersects the AVC curve at AVC's minimum point.
The shutdown rule says a firm produces in the short run only if price is at least equal to minimum AVC; below that, shutting down loses less money.
If price is between AVC and ATC, the firm operates at a loss in the short run because revenue covers variable costs and part of fixed costs.
In the long run all costs are variable (EK PRD-1.A.9), so the AVC versus ATC distinction only exists in the short run.
Average variable cost is total variable cost divided by output (AVC = TVC/Q). It measures the per-unit cost of adjustable inputs like labor and materials, and it sets the firm's short-run shutdown point at its minimum.
ATC includes average fixed cost; AVC leaves it out (ATC = AVC + AFC). Use ATC to determine profit or loss and the long-run exit decision, and use AVC to determine the short-run shutdown decision.
No, not in the short run. A firm shuts down only when price falls below minimum AVC. Between AVC and ATC, the firm loses money but keeps producing, because revenue covers all variable costs plus some of the fixed costs it owes either way.
Because of basic averaging math. When the cost of the next unit (MC) is below the current average, it drags AVC down; when MC is above, it pulls AVC up. The only place AVC can hit its minimum is where MC equals it.
No. In the long run, firms can adjust all inputs, so every cost is variable and AVC merges with ATC into the long-run average total cost (LRATC) curve. That curve's shape reflects economies, diseconomies, or constant returns to scale.