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Fundamentals of Business Economics and Management · Theory of Demand and Supply

Change in Quantity Demanded vs Change in Demand: Movement and Shift

Updated 10 October 2026 · Fact-checked

A change in quantity demanded is a movement along the same demand curve, caused only by a change in the good's own price (extension or contraction). A change in demand is a shift of the whole curve, caused by any other factor (increase or decrease). To solve, ask: did the good's own price change?

Understand Change in Quantity Demanded vs Change in Demand

A demand curve shows how much of a good buyers will purchase at each price, while everything else stays the same. That 'everything else' includes income, tastes, prices of related goods, expectations and population.

Now think about what can change. If only the price of the good itself changes, you slide up or down the same curve. This is a change in quantity demanded. A fall in price gives an extension of demand (quantity rises). A rise in price gives a contraction of demand (quantity falls). The curve does not move.

If any other factor changes, buyers want a different quantity at every price. The whole curve moves. This is a change in demand. A rightward shift is an increase in demand. A leftward shift is a decrease in demand.

Example: Samosa price falls from ₹20 to ₹15 and you buy more. That is extension. Now your pocket money rises and you buy more samosas at ₹20 itself. That is an increase in demand.

The words matter. 'Quantity demanded' means a point on the curve. 'Demand' means the whole curve or schedule.

Key formulas to remember

Movement along the curve
Own price changes, other factors constant → change in quantity demanded
Price falls → extension. Price rises → contraction. Same curve.
Shift of the curve
Any other determinant changes, price constant → change in demand
Rightward shift = increase. Leftward shift = decrease. New curve.
Factors that shift demand
Income, tastes, prices of related goods, expectations, population
Remember these as the 'other than own price' factors.
Related goods effect
Substitute price ↑ → demand ↑; Complement price ↑ → demand ↓
Applies to demand for the other good, not the good whose price rose.
Income effect on shifts
Normal good: income ↑ → demand ↑; Inferior good: income ↑ → demand ↓
Inferior goods behave the opposite way.

How to solve Change in Quantity Demanded vs Change in Demand questions

Use this method for any question that asks you to classify a change or name the correct term.

  1. 1Identify the good whose demand is being discussed.
  2. 2Ask: what changed? Note the one cause given in the question.
  3. 3If the cause is the good's own price, it is a change in quantity demanded. Go to step 3. Otherwise it is a change in demand. Go to step 4.
  4. 4For own price: price fall means extension, price rise means contraction. The movement is along the same curve.
  5. 5For other causes: decide if buyers want more or less at the same price. More means increase (right shift). Less means decrease (left shift).
  6. 6For related goods, check if the other good is a substitute or complement, and note whose price changed.
  7. 7Match your answer to the exact term in the options.

Quickest way: The own-price test

When to use it: Use for any MCQ asking which term describes a given situation.

  1. Find the good in the question and check if its own price changed.
  2. Own price changed: choose extension or contraction. Nothing else.
  3. Own price not changed: choose increase or decrease in demand.
  4. Eliminate options that mix the two ideas, such as 'shift due to price fall'.
  5. Pick the direction: more or less bought at the same price.

Common mistakes in Change in Quantity Demanded vs Change in Demand

  • Calling a price-driven rise in purchases an 'increase in demand'.

    In daily speech, 'demand rises' means people buy more, whatever the reason.

    Fix: If the good's own price caused it, the term is extension of demand, not increase.

  • Shifting the curve when the good's own price changes.

    Students think any change needs a new curve.

    Fix: Own price change means a move along the same curve. Only other factors shift it.

  • Treating a rise in a substitute's price as a fall in demand for that substitute.

    Confusion over which good's demand is being asked about.

    Fix: If tea gets costlier, demand for coffee increases. Tea itself faces contraction of quantity demanded.

  • Assuming higher income always increases demand.

    Inferior goods are forgotten.

    Fix: For inferior goods, rising income decreases demand. Check whether the good is normal or inferior.

  • Mixing up the direction of extension and contraction.

    Both words sound like 'bigger' and 'smaller' of the curve.

    Fix: Extension means quantity extends (rises) as price falls. Contraction means quantity shrinks as price rises.

Worked examples

Example 1

The price of rice falls from ₹60 per kg to ₹50 per kg and a household buys 12 kg instead of 10 kg a month. Which term describes this?
(A) Increase in demand
(B) Extension of demand
(C) Decrease in demand
(D) Contraction of demand

Show the solution
  1. The good is rice.
  2. The cause is a fall in rice's own price.
  3. So this is a change in quantity demanded, a movement along the same curve.
  4. Price fell and quantity rose, which is extension.
  5. Options A and C describe shifts, so they are out. D describes a price rise.

Answer: (B) Extension of demand

Example 2

Tea and coffee are substitutes. The price of tea rises and, at the unchanged price of coffee, people buy more coffee. What happens to the demand curve for coffee?
(A) Movement down along the curve
(B) Movement up along the curve
(C) Leftward shift
(D) Rightward shift

Show the solution
  1. The good under discussion is coffee.
  2. Coffee's own price has not changed. The cause is tea's price rise.
  3. So this is a change in demand, not in quantity demanded. Options A and B are out.
  4. Tea is a substitute, so buyers move to coffee. They want more coffee at every price.
  5. More at every price means an increase in demand, a rightward shift.

Answer: (D) Rightward shift

Exam tips

  • Look for the phrase 'other things remaining constant' as a signal of movement along the curve.
  • Questions often hide the cause in a story. Underline what changed before reading the options.
  • Learn all four terms as pairs: extension and contraction go with price; increase and decrease go with other factors.
  • For related-goods questions, confirm which good's demand is asked before choosing the direction.
  • With no negative marking, always attempt every question. Eliminate the movement options or the shift options first, and then guess.

Practice questions from Theory of Demand and Supply

Change in Quantity Demanded vs Change in Demand: frequently asked questions

What is the difference between change in quantity demanded and change in demand?

A change in quantity demanded is a movement along the same demand curve caused only by the good's own price. A change in demand is a shift of the whole curve caused by other factors such as income, tastes or related goods' prices.

What are extension and contraction of demand?

Extension of demand means more is bought because the price fell. Contraction means less is bought because the price rose. Both are movements along the same demand curve.

What causes a shift in the demand curve?

A change in income, tastes and preferences, prices of substitutes or complements, expectations about future prices, or population. Each changes how much buyers want at every price.

Does a price change ever shift the demand curve?

The good's own price does not shift its own demand curve. It moves buyers along it. A price change of a related good can shift the demand curve of the good you are studying.