Movement along vs shift in demand curve: what's the difference?

You wrote that a price change shifted demand. It didn't. It moved you along the curve — and that distinction costs marks.

You write: "the price of oil rose, so the demand curve shifted left." That sentence loses marks. Not because you don't understand demand — because the diagram underneath it is built on the wrong idea, and the examiner can see that in one line.

Here's the fix, and it's one sentence: a change in the good's own price moves you along the curve. A change in a non-price determinant shifts it.

The rule

Own-price change = movement along. Non-price determinant = shift.

If the good's own price changes, quantity demanded changes — you move to another point on the same curve. A change in price causes a change in quantity demanded, not a change in demand. That's the sentence to write in the exam.

If income, tastes, expectations, the price of related goods, or the number of consumers changes, demand itself changes. The whole curve shifts.

That's the distinction — and the good's own price is not on that list.

A worked example

Scenario A — the good's own price rises. The price of coffee rises from €2.50 to €3.50. Consumers buy less coffee at the higher price. This is a movement up along the existing demand curve — the curve has not shifted.

Scenario B — consumer incomes fall. Assume coffee is a normal good. Incomes fall. At every price level, consumers now demand less coffee than before. The whole demand curve shifts left — because income is a non-price determinant.

Scenario A shows a point moving along the same curve. Scenario B shows a new demand curve to the left. Draw the wrong one in Paper 1 or Paper 2 and the examiner marks it wrong.

Mia catches this in real time

Students don't lose marks from not knowing the topic. They lose marks because they've practised the wrong sentence twenty times.

When you give Mia an answer that says a price change "shifted" the curve, she spots the faulty model and makes you redraw it — before the wrong version becomes automatic.

Stop practising the wrong answer.

Mia spots the misconception, fixes the thinking, and makes you redraw it correctly.

Across the full IB Economics and Business Management curriculum. Free to start. No card needed.