How to Calculate Average Total Cost
Average total cost equals total cost divided by quantity: ATC = TC ÷ Q, which also equals AFC + AVC.
Formula
ATC = TC ÷ Q = AFC + AVC | AFC = FC ÷ Q | AVC = VC ÷ Q
Steps
- 1Find total cost. TC = fixed costs + variable costs at the chosen output level.
- 2Divide by quantity. ATC = TC ÷ Q — the per-unit cost of production.
- 3Cross-check with the components. ATC should equal AFC + AVC. AFC falls continuously as Q rises since fixed cost is spread over more units.
Worked example
TC = $600 at Q = 40, so ATC = 600 ÷ 40 = $15. If fixed costs are $200, AFC = 200 ÷ 40 = $5 and AVC = 400 ÷ 40 = $10 — and $5 + $10 = $15, matching.
Frequently asked questions
Why is the ATC curve U-shaped?
At low output, falling AFC dominates and ATC declines; at high output, rising AVC (from diminishing returns) dominates and ATC climbs.
How is ATC used to find profit?
Profit = (P − ATC) × Q. If price equals minimum ATC the firm breaks even (zero economic profit); if P < ATC it takes a loss.
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