Average Variable Cost (AVC) is total variable cost divided by the quantity of output (AVC = TVC/Q). In AP Micro, it sets the shutdown rule: in the short run, a firm keeps producing as long as price is at or above AVC, and shuts down if price falls below it.
Average Variable Cost is the variable cost per unit of output. You get it by dividing total variable cost by quantity (AVC = TVC/Q). Variable costs are the costs that change with output, like labor and raw materials. Fixed costs (rent, machinery) are not in here at all, which is exactly what makes AVC useful.
On a graph, AVC is U-shaped. It falls at first because of specialization and the division of labor, then rises because of diminishing marginal returns (EK PRD-1.A.6). The marginal cost (MC) curve cuts through AVC at its minimum point. Here's the intuition behind that: MC is the cost of the next unit, and AVC is your per-unit average. If the next unit costs less than your average, it drags the average down. If it costs more, it pulls the average up. So the average has to bottom out exactly where MC crosses it. Think of it like your GPA: a grade below your average lowers it, a grade above raises it.
AVC lives in Unit 3 (Production, Cost, and the Perfect Competition Model) and shows up in two CED learning objectives. Under AP Micro 3.2.A and 3.2.C, you need to define, graph, and calculate AVC from tables or cost curves. Under AP Micro 3.6.A, AVC becomes a decision tool. EK PRD-2.A.1 says a firm decides whether to operate or shut down in the short run by comparing price to AVC (or total revenue to total variable cost, which is the same comparison scaled up). Why AVC and not ATC? Because fixed costs are sunk in the short run. The firm pays them whether it produces or not, so the only question is whether revenue covers the costs it can actually avoid, the variable ones. If price covers AVC, every unit sold at least chips away at the fixed-cost bill. If price drops below AVC, producing makes losses worse, so the firm shuts down. This logic is the backbone of short-run supply in perfect competition.
Keep studying AP Microeconomics Unit 3
Marginal Cost (MC) (Unit 3)
MC intersects AVC at AVC's minimum point. When MC is below AVC, AVC is falling; when MC is above AVC, AVC is rising. This relationship is one of the most reliable MCQ setups in Unit 3, and it also defines the firm's short-run supply curve, which is the MC curve above minimum AVC.
Average Total Cost (ATC) (Unit 3)
ATC = AVC + AFC, so the vertical gap between the ATC and AVC curves is average fixed cost. That gap shrinks as output grows because fixed cost gets spread over more units. ATC tells you whether the firm is profitable; AVC tells you whether it should produce at all.
Diminishing Marginal Returns (Unit 3)
Diminishing marginal returns are the production-side reason AVC eventually rises. As each added worker contributes less extra output, the variable cost per unit climbs. The U-shape of AVC is really the productivity story from Topic 3.1 translated into dollars.
Long Run (Unit 3)
AVC governs the short-run shutdown decision, but the long-run exit decision uses ATC instead. In the long run nothing is fixed, so a firm exits when price stays below ATC (EK PRD-2.A.2). Keeping these two thresholds straight is the classic 3.6 exam trap.
AVC gets tested three ways. First, calculation questions give you a cost table and ask you to compute AVC (or back out TVC from AVC and Q), aligned to 3.2.C. Second, curve-relationship MCQs ask what must be true when MC is above or below AVC. The answer is always about the direction AVC is moving: MC below AVC means AVC is falling, MC above AVC means AVC is rising, and MC crosses both AVC and ATC at their minimum points. Third, shutdown questions ask when a perfectly competitive firm should shut down in the short run, and the answer hinges on price falling below minimum AVC. On FRQs, you'll often draw a perfectly competitive firm's cost curves and identify the shutdown price or the range of prices where the firm produces at a loss but stays open (between minimum AVC and minimum ATC). Label your AVC curve and put MC through its minimum, because graders check that geometry.
ATC includes fixed costs; AVC doesn't (ATC = AVC + AFC). They answer different questions. Compare price to ATC to find profit or loss. Compare price to AVC to decide whether to produce at all in the short run. A firm with price between minimum AVC and minimum ATC is losing money but should keep operating, because revenue covers variable costs and pays off part of the fixed costs it owes anyway. Mixing these up is the single most common error on Topic 3.6 questions.
AVC equals total variable cost divided by output (AVC = TVC/Q), and it excludes all fixed costs.
The shutdown rule says a firm produces in the short run as long as price is at or above minimum AVC, and shuts down if price falls below it.
The MC curve crosses the AVC curve at AVC's minimum point, so MC below AVC means AVC is falling and MC above AVC means AVC is rising.
AVC is U-shaped because specialization lowers per-unit cost at first, and diminishing marginal returns push it back up.
If price is between minimum AVC and minimum ATC, the firm operates at a loss in the short run but should not shut down, since revenue covers variable costs and some fixed costs.
The short-run shutdown decision uses AVC, but the long-run exit decision uses ATC, because all costs become variable in the long run.
Average variable cost is total variable cost divided by quantity of output (AVC = TVC/Q). It measures the per-unit cost of inputs that change with output, like labor and materials, and it sets the short-run shutdown threshold in Topic 3.6.
No. In the short run, a firm losing money should keep producing as long as price covers AVC, because revenue beyond variable costs helps pay fixed costs it owes either way. Shutting down only makes sense when price falls below minimum AVC.
ATC includes average fixed cost and AVC doesn't, so ATC = AVC + AFC. Price versus ATC tells you profit or loss; price versus AVC tells you whether to produce at all in the short run.
Because marginal cost is the cost of the next unit. When the next unit costs less than the average, it pulls the average down; when it costs more, it pulls the average up. So the average must hit its lowest point exactly where MC crosses it, just like a test grade and your GPA.
Specialization and the division of labor make early units cheaper, so AVC falls at first. Then diminishing marginal returns kick in, each added worker produces less extra output, and the variable cost per unit rises.