Supply curve

Topic: Theory of the Firm, Supply and Perfect Competition · NCERT: Class 9, Ch 9 "The Price Puzzle: What Drives the Market"; Class 12, Ch 4 "The Theory of the Firm under Perfect Competition"

Meaning

A supply curve is a graph that shows how much output a firm chooses to sell at each market price. Technology and factor prices (the prices of inputs like wages, rent and interest) stay fixed along the curve. Price (p) goes on the y-axis and output (q) on the x-axis.

For a firm under perfect competition, the supply curve is not the whole marginal cost curve:

• Short run: it is the rising part of the SMC curve, starting at minimum AVC.
• Long run: it is the rising part of the LRMC curve, starting at minimum LRAC.

It matters because it tells us when a firm keeps producing, when it runs at a loss and when it shuts down. This logic sits behind policy on sick units, sugar mills and the IBC.

Explanation

Basic terms, and movement vs shift

• Supply: the quantity a firm chooses to sell at a given price, with technology and factor prices held fixed.
• Supply schedule: a table showing the quantity sold at different prices. The supply curve is the graph of the same table.
• Movement along the curve: only the good's own price changes. The firm moves to a new point on the same curve.
• Shift of the curve: technology or factor prices change, so the whole curve moves.
• Better technology or cheaper inputs → shift to the right (more supplied at each price).
• Costlier inputs or a per-unit tax → shift to the left.

Cost terms behind the curve

• TFC (total fixed cost): cost that does not change with output, e.g. factory rent or an aircraft lease. It exists only in the short run.
• TVC (total variable cost): cost that rises with output, e.g. raw material, fuel and daily wages.
• AVC = TVC ÷ q. SAC = (TFC + TVC) ÷ q = AFC + AVC.
• SMC (short-run marginal cost): the extra cost of one more unit. SMC = ΔTC ÷ Δq.
• SMC cuts AVC and SAC at their lowest points:
• When SMC is below the average, each new unit pulls the average down.
• When SMC is above the average, each new unit pulls the average up.

• So SMC crosses each average exactly at its minimum.

• Normal profit: the least profit that keeps the owner in this business. It equals the owner's opportunity cost (what they could earn elsewhere). Economists count it as a cost, so at normal profit TR = TC.

• Sunk cost: a cost already paid that cannot be recovered, whether the firm produces or not.

Three conditions and the short-run supply curve

A competitive firm is a price-taker. It can sell any quantity at the market price, so p = MR = AR. It produces a positive q only if:

1. p = MC at that q.
2. MC is rising at that q. On the falling part of MC, one more unit adds more to revenue than to cost, so that point is not the best choice.
3. p ≥ AVC in the short run, or p ≥ LRAC in the long run.

Shape of the short-run curve (Class 12 NCERT, Fig 4.8):

• If p ≥ min AVC, the firm sets p = SMC on the rising part of SMC and supplies that output.
• If p < min AVC, it produces zero, because revenue cannot even cover variable cost.
• So the curve runs up the y-axis (q = 0) to min AVC, then jumps to the rising SMC. This break makes the curve discontinuous at min AVC.

Why a firm produces at a loss (the sunk-cost logic):

• If it shuts down, it still pays TFC, so its loss = TFC.
• If it produces and p ≥ AVC, revenue covers all of TVC and pays part of TFC.
• So the loss from producing is smaller than TFC, and producing is better.

Two key points on the curve:

• Shut-down point: the last price-output point with positive output. In the short run it is at min AVC.
• Break-even point: where the firm earns only normal profit (economic profit = 0). In the short run it is at min SAC.
• Min SAC lies above and to the right of min AVC. The gap between them is AFC, so the break-even price is higher than the shut-down price.

Price range	Decision	Outcome
p < min AVC	Shut down (q = 0)	Loses TFC only
min AVC ≤ p < min SAC	Produce where p = SMC	Loss, but covers all variable cost and part of fixed cost
p = min SAC	Produce	Break-even: normal profit only
p > min SAC	Produce	Super-normal profit (TR > TC)

Worked example: TFC = ₹100. At q = 10, TVC = ₹200, so AVC = ₹20 (taken as min AVC) and SAC = ₹30 (taken as min SAC). TC = ₹300.

Price	TR	Profit if producing	Loss if shut (= TFC)	Decision
₹15	₹150	−₹150	−₹100	Shut down
₹25	₹250	−₹50	−₹100	Produce (covers TVC ₹200 + ₹50 of TFC)
₹30	₹300	0	−₹100	Break-even
₹35	₹350	+₹50	−₹100	Super-normal profit

• Shut-down price = ₹20 (min AVC). Break-even price = ₹30 (min SAC).

Long-run supply curve

• Definition (Class 12 NCERT, Fig 4.10): the rising part of LRMC from and above min LRAC. Output is zero below min LRAC.
• Why the two points merge:
• In the long run all inputs are variable, so there is no fixed cost, and LRAC plays the role of AVC.
• There is no fixed cost left to partly cover, so if p < min LRAC the firm exits.
• So shut-down point = break-even point = min LRAC.

Feature	Short run	Long run
Supply curve	Rising SMC from min AVC	Rising LRMC from min LRAC
Shut-down point	min AVC	min LRAC
Break-even point	min SAC	min LRAC (same point)
Can it run at a loss?	Yes, if p ≥ AVC	No. It must exit.

In India

• Short run: loss-making firms keep running. Sugar mills, airlines and power distribution companies (discoms) often operate at a loss.
• Their plants, aircraft leases and power networks are sunk fixed costs.

• Revenue still covers operating (variable) cost. This is the "min AVC ≤ p < min SAC" band.

• Support for firms in the loss band: sugar mills that borrowed under the Sugar Development Fund Act, 1982 can get their SDF loans restructured. The Department of Food and Public Distribution issued guidelines on 03.01.2022 for mills that are "financially weak but economically viable" [3].

• In theory terms, the government is betting that price will cover average cost in the long run.

• Scale of sickness: RBI provisional data showed 5,16,619 sick MSMEs in March 2015 [2].

• Long run: exit when price stays below average cost.
• 78 unviable National Textile Corporation (NTC) mills were closed during 2002–2011. This happened under revival schemes approved by the BIFR (Board for Industrial and Financial Reconstruction) in 2002, 2006 and 2008 [4].

• The government approved 19 sick and loss-making CPSEs (Central Public Sector Enterprises) or their units for closure. Closure was completed for 2 of them: Indian Oil-CREDA Biofuel Ltd and HPCL-CREDA Biofuel Ltd [5].

• The legal exit route is the Insolvency and Bankruptcy Code (IBC), 2016.

• When a firm defaults on its debt, a Committee of Creditors (CoC) decides whether to revive it or liquidate it (sell off its assets). The NCLT (National Company Law Tribunal) oversees cases for companies, and the DRT for individuals [6].
• The original time limit was 180 days [6]. The current outer limit for the CIRP (Corporate Insolvency Resolution Process) is 330 days [7].
• Order of payment in liquidation: insolvency resolution costs → secured creditors and workers' dues → unsecured creditors → government dues → priority shareholders → equity shareholders [6][7].
• Till March 2026: 8,987 CIRPs admitted and 1,419 firms resolved through approved plans. Creditors recovered over ₹4 lakh crore, which is 95% of fair value and 167% of liquidation value [7].

Don't confuse with

• Whole SMC curve: only the rising part of SMC at and above min AVC is the short-run supply curve. The falling part, and the part below min AVC, are not on it.
• Shut-down point vs break-even point: in the short run, shut-down is at min AVC and break-even is at min SAC. In the long run both are at min LRAC.
• Movement along vs shift of the supply curve: a change in the good's own price causes a movement along the curve. A change in technology, input prices or a per-unit tax shifts it.
• Normal profit vs zero accounting profit: at break-even, economic profit is zero, but the firm still earns normal profit (TR = TC, with the owner's opportunity cost counted as cost).

Prelims Hooks

• The short-run supply curve of a competitive firm is the rising part of SMC from min AVC. Below min AVC, output is zero, so the curve is discontinuous at min AVC.
• The three conditions for positive output are: p = MC; MC rising; p ≥ AVC (short run) or p ≥ LRAC (long run).
• If a firm shuts down in the short run, its loss equals TFC, not zero.
• If min AVC ≤ p < min SAC, the firm produces at a loss. It covers all variable cost and part of fixed cost.
• SMC cuts both AVC and SAC at their minimum points. Technology and factor prices are constant along one supply curve.
• Under IBC 2016, the CIRP outer limit is 330 days, and the NCLT orders liquidation [7].

Mains Points

• Keeping sick units alive (GS-III, industry and PSUs): a unit that covers its variable cost should keep running in the short run. Examples are sugar mills, discoms and loss-making CPSEs.
• Help such as SDF loan restructuring (2022) is justified only for units that are "economically viable" [3].

• If price stays below average cost, the support becomes a permanent subsidy and delays long-run exit.

• Sunk-cost logic vs political economy: workers, farmers' cane dues and regional jobs push governments to keep units open even below min AVC, which is inefficient.

• Closing unviable units, such as the 78 NTC mills (2002–11) [4] and the CPSE closures [5], applies the theory but has social costs.

• A good answer pairs exit with worker rehabilitation.

• IBC as the long-run exit mechanism: a time limit (330 days) and a fixed order of payment make exit faster and more predictable. Recovery of 167% of liquidation value till March 2026 shows that reviving a firm as a going concern often beats selling its assets piece by piece [7].

• In discoms and airlines, high fixed costs mean long periods of running at a loss. Tariff reform that brings price up to average cost is needed, or the long-run result is repeated bailouts.

Related concepts

• Supply
• Supply schedule
• Short run supply curve of a firm
• Long run supply curve of a firm
• Shutdown point
• Break-even point

Read more

• The firm's supply curve: short run, long run, shut-down and break-even points