Market demand

Also called: market demand curve · Topic: Consumer Behaviour, Demand and Elasticity · NCERT: Class 9, Ch 9 "The Price Puzzle: What Drives the Market"; Class 12, Ch 2 "Theory of Consumer Behaviour"; Class 12, Ch 5 "Market Equilibrium"

Meaning

Market demand is the total quantity of a good that all consumers in a market want to buy at each possible price, when other things (income, tastes, prices of related goods) stay the same.

Formula: Q_market(p) = q₁(p) + q₂(p) + … + qₙ(p), where qᵢ(p) is buyer i's demand at price p.

It matters because firms, markets and governments deal with the whole group of buyers, not with one person. Prices, output, taxes and subsidies are all judged against the market demand curve.

Explanation

How it is built: horizontal summation

• Individual demand: how much one consumer wants to buy at each price, with other things unchanged.
• Market demand curve: a graph that shows how much the whole market will buy at every price.
• It is made by horizontal summation:
• Pick a price.
• Read how much each person buys at that price.

• Add these quantities.

• Quantity is on the horizontal axis (x-axis), so the adding happens along that axis.

• Prices are never added. Every buyer faces the same market price.
• Class 9 example (Table 9.1):

Price	Srivalli	Alex	Israt	Market demand
₹150	1 kg	2 kg	3 kg	6 kg
₹100	2 kg	4 kg	6 kg	12 kg
₹50	3 kg	6 kg	9 kg	18 kg

• At ₹100: 2 + 4 + 6 = 12 kg. The price stays ₹100. It does not become ₹300.
• Each person's curve slopes downward, so the market curve slopes downward too. This is the law of demand for the market: price falls → quantity demanded rises.

Adding linear demands: the kinked curve

• Linear demand: a demand curve that is a straight line, written q = a − bp.
• a = quantity bought when the price is zero.

• b = how many units demand falls for each ₹1 rise in price.

• Choke price (cut-off price): the price at which a buyer's demand becomes zero and they stop buying.

• Class 12 example: d₁(p) = 10 − p (stops buying above ₹10) and d₂(p) = 15 − p (stops buying above ₹15).
• p ≤ 10 → both buy → (10 − p) + (15 − p) = 25 − 2p
• 10 < p ≤ 15 → only consumer 2 buys → 15 − p

• p > 15 → nobody buys → 0

• Kink (a sharp bend in the curve): at p = 10, q = 5.

• Check: 25 − 2(10) = 5, and 15 − 10 = 5. Both pieces meet at the same point.

• Above ₹10 only one buyer responds to price. Below ₹10 two buyers respond. So the curve is flatter below ₹10 (slope −2 in q terms against −1 above).

• Worked numbers:

• p = 4 → 25 − 8 = 17 (6 + 11)
• p = 12 → 3 (0 + 3)

• p = 16 → 0

• Common mistake: using 25 − 2p at every price.

• At p = 12 this gives 1. The correct answer is 15 − 12 = 3.

• Consumer 1's "10 − 12 = −2" must be counted as zero. Negative quantities do not exist.

• Second drill (unequal cut-offs): d₁ = 20 − p (buys up to ₹20) and d₂ = 30 − 2p (buys up to ₹15).

• p ≤ 15 → 50 − 3p
• 15 < p ≤ 20 → 20 − p
• p > 20 → 0

• Kink at p = 15, q = 5 (50 − 45 = 5; 20 − 15 = 5).

• Class 12 table drill: p = 1 → 9 + 24 = 33; p = 6 → 4 + 12 = 16.

• Exam method:
• Find each buyer's cut-off price.
• Split the price axis at those cut-offs.
• In each price range, add only the buyers who are actually buying.

Identical consumers

• If there are n identical consumers, market demand = n × individual demand.
• Class 12 exercise: 20 consumers, each with d(p) = 10 − 3p.
• Market demand = 20 × (10 − 3p) = 200 − 60p for p ≤ 10/3 (about ₹3.33).
• 0 for p > 10/3.

• Check at p = 2: one person buys 10 − 6 = 4. The market buys 20 × 4 = 80 (= 200 − 120).

• Everyone has the same choke price, so the market's choke price is the same too. No kink.

What shifts market demand

• Determinant: a factor other than the good's own price that decides how much is demanded.
• For one person: income, tastes, and prices of related goods.

• Market demand adds one more: the number of buyers.

• Standard theory lists the number of consumers in the market as a factor that shifts the demand curve [2].

• More buyers → the curve shifts right:
• Population grows, new markets open, or online selling reaches new areas.
• At every price, more people are buying.

• So more is demanded at every price, even if no single person's demand changes.

• Movement vs shift:

• Change in the good's own price → movement along the market curve.
• Change in the number of buyers, income, tastes or related prices → shift of the whole curve.

In India

• Market demand is a theory concept. India's large and growing buyer base is a clear example of the number of buyers shifting it.
• Population: India's population is projected at about 142.6 crore (1,425.9 million) in 2026. About 92.4 crore (923.9 million) of these are of working age (15–59). Source: Technical Group on Population Projections, 2011–2036 (July 2020) [3].
• Internet reach: India had 101.78 crore internet subscribers as of 30 September 2025: 42.77 crore rural and 59.01 crore urban [4].
• Village connectivity: 98.09% of villages have internet access [4].
• What this means for market demand:
• Each new online buyer is one more "qᵢ" in the horizontal sum.
• So wider e-commerce reach pushes market demand for many goods to the right.

• Platforms such as ONDC and e-Saras bring rural buyers into national markets.

• Kinks in real Indian markets:

• When prices of items like LPG refills or pulses spike, poorer households stop buying altogether.
• Whole groups of buyers leave the market at once, which is a kink in the market curve.

Don't confuse with

• Individual demand: one buyer's demand. It does not depend on the number of buyers. Market demand does.
• Vertical summation: adding prices at a given quantity. Market demand for private goods adds quantities at a given price. Prices are never added.
• Slope vs price elasticity of demand (eₚ):
• Slope = change in quantity for a change in price, in absolute units (kg per ₹).
• eₚ = % change in quantity demanded ÷ % change in price.
• The market curve looks flatter only because its quantities are bigger. That does not make it more elastic.
• This is the error in the Class 9 "Don't miss out" box. It says the flatter market curve means the market is "more responsive" to price.

• Proof from Table 9.1: market demand = 6 × Srivalli's demand. From ₹150 to ₹50, Srivalli goes 1 → 3 kg (+200%) and the market goes 6 → 18 kg (+200%). The price change is the same for both (−66.7%). So eₚ is the same.

• Movement along vs shift of the market curve: an own-price change causes a movement along the curve. A change in the number of buyers, income, tastes or related prices causes a shift.

Prelims Hooks

• Market demand = horizontal summation of individual demand curves. Quantities are added at a given price. Prices are never added.
• n identical consumers → market demand = n × individual demand. Example: 20 × (10 − 3p) = 200 − 60p, which becomes zero above p = 10/3. No kink.
• d₁ = 10 − p and d₂ = 15 − p give 25 − 2p (p ≤ 10), 15 − p (10 < p ≤ 15) and 0 (p > 15). Kink at p = 10, q = 5. A kink appears only when buyers have different choke prices.
• Number of buyers is a determinant of market demand but not of individual demand. A rise in it shifts the curve right [2].
• Trap: "a flatter market demand curve means the market is more price-elastic" is false. When market demand = k × individual demand, elasticities are equal. With different buyers, market eₚ is the quantity-weighted average of individual elasticities. Example at p = 5 (d₁ = 10 − p, d₂ = 15 − p): (5/15)(−1) + (10/15)(−0.5) = −0.67 = market eₚ (−2 × 5/15).
• India: 101.78 crore internet subscribers (30 Sept 2025), of which 42.77 crore are rural [4]. Projected population 1,425.9 million (2026) [3].

Mains Points

• Demographic dividend and market size (GS-III):
• About 92.4 crore people of working age are projected for 2026 [3].
• More earning buyers → market demand shifts right → firms can produce at scale.

• This supports jobs-led growth, which turns a large population into real purchasing power.

• Digital reach widens markets (GS-III, inclusive growth):

• 42.77 crore rural internet users (Sept 2025) [4], plus platforms such as ONDC and e-Saras, bring new buyers into national markets.
• Market demand rises even though no single person's demand has risen. This helps small sellers.

• The gain depends on better last-mile delivery and digital literacy.

• Policy must use elasticity, not slope:

• To judge how GST rate changes, fuel price changes or subsidies will affect consumption, policymakers need the percentage response of each buyer group.
• Market elasticity is only a weighted average. So a price rise can hurt poor, price-sensitive households badly even when total demand looks "inelastic".
• When prices rise past what poorer households can pay, they leave the market (the kink). This is the case for targeted transfers and price-band measures such as PMUY subsidies and buffer-stock releases of pulses.

Related concepts

• Horizontal summation

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