In AP Microeconomics, a fixed cost is a cost that does not change with the level of output in the short run. Total fixed cost stays constant at all output levels, including zero (EK PRD-1.A.5), which is why firms ignore fixed costs in the short-run shutdown decision and only escape them in the long run.
A fixed cost is any cost a firm must pay regardless of how much it produces. Rent on the factory, the lease on the equipment, the insurance bill, all of these are owed whether the firm makes 1,000 units or shuts the lights off and makes nothing. That last part is the detail the CED hammers on. Per EK PRD-1.A.5, total fixed cost (TFC) remains constant at all output levels, including zero output. If you see a cost column in a table that doesn't budge as quantity changes, you've found fixed cost. And whatever total cost equals at zero output? That entire amount is fixed cost, because variable cost is zero when nothing is produced.
Fixed costs combine with variable costs to determine total cost (EK PRD-1.A.4), so TC = TFC + TVC at every output level. On a per-unit basis, average fixed cost (AFC = TFC/Q) falls continuously as output rises, since you're spreading the same dollar amount over more and more units. That's why AFC slopes downward forever and never turns back up. It's also why the gap between the ATC and AVC curves shrinks as you move right on a cost-curve graph. That shrinking gap IS average fixed cost.
Fixed cost lives in Unit 3 (Production, Cost, and the Perfect Competition Model), specifically Topics 3.2 and 3.6. Under learning objective 3.2.A you have to define and graph it; under 3.2.C you have to calculate it from tables and graphs. But the real payoff is learning objective 3.6.A, the shutdown decision. Per EK PRD-2.A.1, a firm decides whether to operate or shut down by comparing price to average variable cost, not average total cost. Fixed costs are deliberately left out of that comparison because the firm pays them either way in the short run. They're sunk for the operating decision. Then EK PRD-2.A.2 flips the script for the long run, where factors that were fixed become variable, so firms can fully exit and escape those costs. Understanding fixed cost is literally what separates the short run from the long run in AP Micro.
Keep studying AP Microeconomics Unit 3
Variable Cost (Unit 3)
Variable cost is fixed cost's mirror image. It changes with output and equals zero at zero output. Together they make total cost (EK PRD-1.A.4), and the shutdown rule only compares price to AVC precisely because fixed costs can't be avoided in the short run.
Average Total Cost (ATC) and Average Variable Cost (AVC) (Unit 3)
ATC minus AVC equals AFC at every quantity. Since AFC always falls as output grows, the ATC and AVC curves get closer and closer together as you move right on the graph but never touch. This vertical gap shows up constantly in graph-reading questions.
Shutdown vs. Exit Decisions (Unit 3, Topic 3.6)
A firm losing money but covering its variable costs keeps producing in the short run, because shutting down means still paying fixed costs while earning zero revenue. Producing at least covers some of the fixed cost bill. In the long run those costs become escapable, so persistent losses trigger exit instead.
Long Run (Unit 3)
The economic definition of the long run is built on fixed cost. The long run is simply the time horizon where every input, and therefore every cost, becomes variable. No fixed costs means no shutdown rule, just enter or exit based on economic profit or loss.
Multiple-choice questions test fixed cost in a few predictable ways. You'll see stems like "which cost remains unchanged regardless of output" (the answer is total fixed cost), "what happens to AFC as output increases" (it falls continuously), and questions about which curve is the sum of AFC and AVC (the U-shaped ATC). Calculation questions give you a cost table and ask you to back out TFC, often by reading total cost at zero output. On FRQs, fixed cost is the engine behind shutdown and exit reasoning. The 2023 FRQ Q3 gave a graph with ATC, AVC, and MC curves for a profit-maximizing firm, exactly the setup where the ATC-AVC gap and the shutdown rule come into play. The 2019 FRQ on FillUp's gas station monopoly and the 2021 and 2023 perfect competition FRQs all hinge on profit and loss analysis that requires knowing which costs a firm can and can't avoid. The classic point-earner is explaining why a firm with P above AVC but below ATC keeps producing despite losses. If your answer doesn't mention fixed costs, you're probably not earning that point.
Fixed costs stay constant as output changes; variable costs rise with output. The quick test is zero output. At Q = 0, variable cost is zero but fixed cost is still owed in full. The exam confusion usually comes from per-unit versions, where things flip in feel. Average fixed cost always falls as output rises (same dollars spread over more units), while average variable cost eventually rises because of diminishing marginal returns. Don't let "fixed" trick you into thinking AFC is a flat line. Total fixed cost is flat; average fixed cost is a downward slide.
Total fixed cost stays constant at every output level, including zero output, so total cost at Q = 0 equals total fixed cost.
Average fixed cost (TFC divided by Q) falls continuously as output increases, which is why the gap between the ATC and AVC curves shrinks as quantity grows.
Fixed costs are ignored in the short-run shutdown decision; a firm produces as long as price covers average variable cost, because fixed costs are owed either way.
A firm earning a loss but covering its variable costs should keep operating in the short run, since producing offsets part of the fixed costs it would otherwise pay with zero revenue.
In the long run, costs that were fixed become variable, which is why firms can fully exit a market and why long-run decisions hinge on economic profit instead of the shutdown rule.
Total cost equals total fixed cost plus total variable cost (TC = TFC + TVC) at every level of output.
A fixed cost is a cost that doesn't change with output in the short run, like rent or insurance. Per EK PRD-1.A.5, total fixed cost stays constant at all output levels, including when the firm produces nothing.
No, not necessarily. The shutdown rule compares price to average variable cost, not total cost. If P is above AVC, the firm keeps producing even at a loss, because the extra revenue helps pay down fixed costs it owes no matter what.
Fixed costs don't change with output and must be paid even at zero production; variable costs rise as output rises and are zero when output is zero. Together they sum to total cost (TC = TFC + TVC).
No. Total fixed cost is constant, but average fixed cost (TFC/Q) falls as output increases because the same total is spread over more units. The AFC curve slopes downward at every quantity and never rises.
Look at total cost when output is zero; that entire number is total fixed cost, since variable cost is zero with no production. If the table starts above zero output, subtract total variable cost from total cost at any quantity to get TFC.
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