AP Syllabus focus: ‘Short-run equilibrium occurs where aggregate output demanded equals aggregate output supplied, at the intersection of AD and SRAS.’
Short-run equilibrium in the AD–AS model identifies the economy’s current price level and real output when spending plans match firms’ short-run production, given sticky input prices and existing expectations.
Core idea: where AD meets SRAS
Short-run equilibrium on the graph
In the short run, equilibrium occurs at the point where the aggregate demand (AD) curve intersects the short-run aggregate supply (SRAS) curve. That intersection pins down:
the equilibrium price level (vertical axis), and
the equilibrium level of real GDP (real output) (horizontal axis).
This is the model’s key organising statement for this subtopic: short-run equilibrium occurs where aggregate output demanded equals aggregate output supplied.
Short-run equilibrium (AD–AS): The price level and real output at which aggregate output demanded equals aggregate output supplied, where AD intersects SRAS.
Even though the equilibrium is “short run,” it is still an equilibrium: there is no tendency for firms, households, or the government to change total planned spending or total production at that price level, given the current AD and SRAS curves.
The equilibrium condition (notation)
To express the same idea algebraically, macroeconomists often write output as .
= Quantity of real output demanded at a given price level (real GDP)
= Quantity of real output supplied at a given price level (real GDP)
This condition is not a “market-clearing” statement for one product; it summarises economy-wide planned spending versus economy-wide production.
Why the economy moves toward the intersection
Disequilibrium above or below the intersection
If the economy is not at the AD–SRAS intersection, there is a mismatch between what buyers want to purchase (in real terms) and what firms are producing:
Excess demand (shortage) for real output: quantity demanded exceeds quantity supplied at the current price level.
Excess supply (surplus) of real output: quantity supplied exceeds quantity demanded at the current price level.
In the AD–AS framework, these mismatches create pressure for the price level and real output to change until the intersection is reached.
Adjustment logic (price level as the key signal)
A simple way to describe the movement to equilibrium:
If there is excess demand, firms experience unexpectedly low inventories and stronger sales.
Firms expand production in the short run (moving up along SRAS).
The price level tends to rise as firms raise prices and compete for inputs at existing contracts.
If there is excess supply, firms accumulate inventories and sales disappoint.
Firms cut production in the short run (moving down along SRAS).
The price level tends to fall as firms discount goods and reduce output.
This story stays within the model’s short-run boundary: wages and some input prices do not fully adjust immediately, so output can change when the price level changes.
What short-run equilibrium does (and does not) tell you
What you can read directly
At the equilibrium point you can identify:
the economy’s current price level
the economy’s current real GDP
the implied short-run consistency between total spending and total production
What is intentionally not determined here
Short-run equilibrium alone does not tell you whether the economy is operating at “full employment” or whether inflation is accelerating; it only identifies the current intersection of AD and SRAS, given their current positions.
FAQ
In many presentations, “output demanded” corresponds to planned spending on domestically produced goods and services (desired real GDP).
In practice, national income accounting uses realised expenditures, so the model’s “demand” is best read as planned spending consistent with a given price level.
Inventories act as a buffer when sales differ from what firms expected.
Sales above expectations reduce inventories, signalling firms to raise output.
Sales below expectations increase inventories, signalling firms to cut output.
Yes. Equilibrium refers to equality of output demanded and supplied at a point in time, not to a stable or slowly changing price level.
A rapidly shifting AD or SRAS curve can move the equilibrium from one period to the next.
The vertical axis is an index such as the GDP deflator or CPI-like measure. What matters is that it represents the overall price level used to translate nominal spending into real output.
No. The AD–AS equilibrium is an economy-wide consistency condition. Individual labour or product markets may still have imbalances even when overall real output demanded equals real output supplied.
Practice Questions
(2 marks) On an AD–AS diagram, identify the short-run equilibrium and state what it determines.
Identifies that short-run equilibrium is where AD intersects SRAS (1).
States it determines the equilibrium price level and equilibrium real output (real GDP) (1).
(5 marks) Explain how a short-run equilibrium is restored if the economy is initially at a price level where real output demanded is greater than real output supplied.
Recognises the situation as excess demand/shortage: (1).
Explains firms experience unplanned inventory declines/stronger sales (1).
Explains firms increase production in the short run (movement along SRAS) (1).
Explains the price level rises as firms raise prices in response to demand pressures (1).
States equilibrium is restored when AD and SRAS intersect so (1).
