Supply

Topic: Theory of the Firm, Supply and Perfect Competition · NCERT: Class 7, Ch 12 "Understanding Markets"; Class 9, Ch 9 "The Price Puzzle: What Drives the Market"; Class 12, Ch 4 "The Theory of the Firm under Perfect Competition"

Meaning

Supply is the quantity of a good that a firm chooses to sell at a given price, while its technology and factor prices (the prices of inputs such as wages, rent and interest) stay fixed.

Supply is one half of every market, and demand is the other. The price we pay for sugar, air tickets or electricity depends on how much firms are willing to sell at each price. This entry shows how a firm makes that choice, why it sometimes keeps selling at a loss, and when it must stop.

• Profit-maximising rule for a price-taking firm: produce where p = MC, on the rising part of MC, with p ≥ AVC in the short run (or p ≥ LRAC in the long run).

Explanation

Supply schedule, supply curve, and movement vs shift

• Supply schedule: a table. It shows the quantity a firm sells at different prices, with technology and factor prices unchanged.
• Supply curve: a graph of the same table. Price (p) goes on the y-axis and output (q) on the x-axis. Technology and factor prices stay constant along one curve.
• Movement along the curve: when the good's own price changes, the firm moves along the same curve.
• Shift of the whole curve: when technology or factor prices change.
• Better technology or cheaper inputs → cost of each unit falls → the curve shifts right (more supply at every price).
• Costlier inputs or a per-unit tax → cost of each unit rises → the curve shifts left.

How a competitive firm decides how much to supply

• Under perfect competition, the firm is a price-taker. It can sell any quantity at the market price, so price = MR = AR (MR is the extra revenue from one more unit, and AR is revenue per unit).
• Key cost terms:
• 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 both AVC and SAC at their lowest points. When SMC is below the average, it pulls the average down. When SMC is above it, it pulls the average up.

• Three conditions for positive output: 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 the firm should keep going. 3. p ≥ AVC (short run), or p ≥ LRAC (long run).

Short-run and long-run supply curves

• Short-run supply curve: the rising part of SMC, from minimum AVC upwards.
• Below min AVC, output is zero at every price.

• So the curve runs vertically along the y-axis (q = 0) up to min AVC and then jumps to the rising SMC. It is discontinuous (it has a break) at min AVC.

• Why a firm keeps producing at a loss (sunk-cost logic):

• A sunk cost is a cost that is already paid and cannot be recovered. In the short run, TFC is sunk.
• If the firm shuts down → it still pays TFC → loss = TFC.
• If it produces with p ≥ AVC → revenue covers all of TVC and part of TFC → loss is smaller than TFC.

• Rule: in the short run, any price that covers variable cost is better than shutting down.

• Shut-down point: the last price-output point with positive output. Short run: min AVC. Long run: min LRAC.

• Break-even point: the point where the firm earns only normal profit (the minimum profit that keeps the owner in this business, i.e. their opportunity cost). Economists count normal profit as a cost, so here TR = TC and economic profit = 0.

• Short run: min SAC. This lies above and to the right of min AVC, and the gap is AFC. So the break-even price is higher than the shut-down price.

• Long-run supply curve: the rising part of LRMC, from minimum LRAC upwards.

• In the long run all inputs are variable, so there is no fixed cost to partly cover.
• If p < min LRAC, the firm exits.
• So shut-down point = break-even point = min LRAC.

Price range (short run)	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

Take TFC = ₹100. At q = 10, TVC = ₹200, so AVC = ₹20, SAC = ₹30, and TC = ₹300. Assume these are the minimum AVC and SAC.

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

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

In India

• Short run: firms that run at a loss but keep operating. Sugar mills, airlines and power distribution companies (discoms) often keep running at a loss.
• Their plant, aircraft leases and power networks are sunk fixed costs.

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

• Policy support for this 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, 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: Insolvency and Bankruptcy Code (IBC), 2016

• When a firm fails to repay its debt, a Committee of Creditors (CoC) decides whether to revive it or liquidate it (sell its assets). The NCLT (National Company Law Tribunal) oversees the process 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

• Stock: the total quantity of a good the firm holds. Supply is only the part it chooses to sell at a given price. Stock is a fixed amount, but supply changes with price.
• Change in quantity supplied vs change in supply: a change in the good's own price moves the firm along the curve. A change in technology or factor prices (or a per-unit tax) shifts the whole curve.
• 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.
• Whole SMC curve vs supply curve: only the rising part of SMC above min AVC is the short-run supply curve. The falling part and the part below min AVC are not.

Prelims Hooks

• Along one supply curve, technology and factor prices are constant. A change in either shifts the curve. A per-unit tax shifts it left.
• The short-run supply curve of a competitive firm is the rising part of SMC at and above min AVC. It is discontinuous at min AVC.
• Short-run shut-down point = min AVC. Short-run break-even point = min SAC. In the long run, both coincide at min LRAC. Watch for questions that swap these.
• A firm that shuts down in the short run loses TFC, not zero.
• At break-even, economic profit is zero but the firm earns normal profit (TR = TC).
• Under IBC 2016, the CIRP outer limit is 330 days and the NCLT oversees corporate insolvency [7].

Mains Points

• Keeping sick units alive (GS-III, industry and PSUs): supply theory says a unit that covers its variable cost should keep running in the short run. Sugar mills, discoms and loss-making CPSEs are examples.
• Support such as SDF loan restructuring (2022) makes sense only for units that are "economically viable" [3].

• If price stays below average cost, support turns into a permanent subsidy and delays the exit that should happen in the long run.

• Sunk-cost logic vs political economy: workers' jobs, farmers' cane dues and regional employment push governments to keep units open even below min AVC. That is economically inefficient. Closures such as the 78 NTC mills (2002–11) [4] and the CPSE closures [5] apply the theory, but they have social costs. A good answer should balance closure 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 running business often beats selling its assets piece by piece [7]. Discoms and airlines have high fixed costs, so they need cost-reflective tariffs and pricing to bring price up to average cost. Without them, the result is repeated bailouts.

Related concepts

• Supply schedule
• Supply curve
• 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