AP Macroeconomics

## Learning Outcomes

- Explain why the short-run aggregate supply curve slopes upward
- Use sticky wages and sticky input costs to explain firm behavior when the price level changes
- Calculate how a change in the price level affects the real wage when nominal wages are fixed
- Distinguish clearly between a movement along SRAS and a shift of SRAS
- Compare short-run aggregate supply with long-run aggregate supply
- Apply SRAS reasoning to AP-style multiple-choice and free-response questions

## AP Macroeconomics Syllabus

For the AP Macroeconomics, you are expected to understand short-run aggregate supply, with a focus on the following syllabus points:

- Know that **SRAS** is upward sloping because some input prices, especially nominal wages, are sticky in the short run
- Explain the chain: higher price level -> input costs lag -> profits rise -> firms increase real output supplied
- Understand that a change in the price level causes a movement along the SRAS curve, not a shift
- Use the relationship **real wage = nominal wage / price level**
- Explain why a fall in the price level can reduce profits and lower real output supplied when wages are sticky
- Identify factors that shift SRAS, including nominal wages, other input prices, productivity, expected future prices, taxes, subsidies, and regulation
- Contrast SRAS with **LRAS**, which is vertical because input prices adjust in the long run

## Test Your Knowledge

_Attempt these questions before reading this article. If you find some difficult or cannot remember the answers, look more closely at that area during your revision._

1. Why does a rise in the price level lead firms to produce more in the short run?
2. If nominal wages stay fixed and the price level rises, what happens to the real wage?
3. What is the difference between a movement along SRAS and a shift of SRAS?
4. Why is LRAS vertical while SRAS is upward sloping?
5. Would a rise in nominal wages shift SRAS or cause movement along it?

## Introduction

Short-run aggregate supply is one of the most tested parts of the AD-AS model because it connects price changes, production, employment, and business costs. On the AP exam, students often know that SRAS slopes upward but lose marks because they cannot explain why.

The core idea is simple but must be stated precisely. In the short run, many firms face **sticky** input costs, especially wages. If the overall price level rises before those input costs fully adjust, firms can sell output at higher prices while paying roughly the same costs for labor and other inputs. That raises profit per unit and gives firms an incentive to increase real output supplied.

> **Key Term: short-run aggregate supply (SRAS)**
> The total real output firms are willing and able to produce at different price levels in the short run.

### Why sticky wages make SRAS slope upward

The most important AP explanation for upward-sloping SRAS is **sticky nominal wages**. In the short run, many wages do not adjust immediately when the price level changes. Workers may be on contracts, firms may avoid frequent pay changes, or information may arrive with a delay. That means output prices can rise faster than wage costs.

Suppose the overall price level rises. Firms now receive more dollars when they sell their goods and services. If nominal wages have not yet risen, labor costs per worker stay the same in dollar terms for now. So firms become more profitable and respond by hiring more labor and producing more output.

This is the chain you should be able to write from memory:

- price level rises
- nominal wages stay temporarily fixed
- real wages fall
- labor becomes effectively cheaper to firms
- profits rise
- firms increase real output supplied
  > **Key Term: sticky wages**
  > Wages that do not adjust immediately when the price level changes.
  >
  > **Key Term: nominal wage**
  > The wage measured in current dollars, not adjusted for changes in the price level.

A common student mistake is to say “prices are sticky, so SRAS slopes upward.” That is too vague for AP Macro. The better explanation is that **input prices**, especially nominal wages, are sticky in the short run.

Another mistake is to say firms “increase aggregate demand.” Firms do not increase aggregate demand here. They increase **real output supplied**.

You should also understand the reverse case. If the price level falls while nominal wages remain fixed, firms receive less for their output but still pay the same wages. Profits shrink, so firms reduce production and employment. That is why lower price levels are associated with less real output supplied along the SRAS curve.

> **Test Tip:** In an FRQ, do not stop at “SRAS is upward sloping because wages are sticky.” Add the full mechanism: “When the price level rises and nominal wages are fixed, real wages fall, labor becomes cheaper to firms, and firms increase output.”

### Real wage, profits, and a worked example

The supporting formula you need is:

$$
\text{Real wage}=\frac{\text{Nominal wage}}{\text{Price level}}
$$

This helps explain why firms react to changes in the price level when nominal wages are sticky.

> **Key Term: real wage**
> The purchasing-power-adjusted wage, found by dividing the nominal wage by the price level.

Here is a worked example.

Suppose a worker is paid a nominal wage of **$20 per hour** and the initial price level is **100**.

Step 1: Calculate the initial real wage

$$
\text{Real wage}=\frac{20}{100}=0.20
$$

Step 2: Now suppose the price level rises to **125**, but the nominal wage stays at **$20**

$$
\text{Real wage}=\frac{20}{125}=0.16
$$

Step 3: Interpret the result

- the real wage fell from **0.20** to **0.16**
- labor is effectively cheaper for firms in real terms
- output prices are higher, but wage costs have not caught up
- profits rise
- firms increase real output supplied

Now reverse it.

If the price level falls from **100** to **80** while the nominal wage stays **$20**:

$$
\text{Real wage}=\frac{20}{80}=0.25
$$

Now the real wage rises from **0.20** to **0.25**. Labor becomes more expensive in real terms, profits fall, and firms reduce output supplied.

This is why the SRAS curve slopes upward instead of vertical in the short run.

Students sometimes ask why firms care about the real wage rather than only the nominal wage. The reason is that firms compare what they pay for inputs with what they receive from selling output. If output prices rise faster than wages, profitability improves even if the dollar wage itself has not changed.

> **Key Term: input costs**
> The costs of resources used in production, such as wages, raw materials, energy, and capital.

You can also explain this without the formula. If a bakery sells bread at higher prices but still pays the same hourly wages for a few months, each loaf sold brings in more revenue relative to cost. The bakery has an incentive to bake and sell more.

> **Test Tip:** If a question gives numbers, calculate the real wage and then state the economic meaning. The calculation alone may not earn full credit if the explanation is missing.

### Movement along SRAS versus a shift of SRAS

This distinction appears constantly in AP multiple-choice questions.

A **change in the price level** causes a **movement along** the SRAS curve.

A change in one of SRAS’s non-price determinants causes the **entire SRAS curve to shift**.

> **Key Term: movement along the SRAS curve**
> A change in quantity of real output supplied caused only by a change in the price level.

If the price level rises from one value to another and all else stays constant, firms move up and right along the existing SRAS curve. If the price level falls, firms move down and left along the same curve.

But if nominal wages rise, or oil prices rise, or productivity changes, or expected future prices change, then firms’ costs or incentives change at every price level. That means SRAS shifts.

Here is the rule:

- **price level changes** -> movement along SRAS
- **nominal wage changes** -> shift of SRAS
- **other input cost changes** -> shift of SRAS
- **productivity changes** -> shift of SRAS
- **expected future price level changes** -> shift of SRAS
- **taxes, subsidies, regulation, supply shocks** -> shift of SRAS

A rise in nominal wages shifts SRAS left because firms face higher costs at every price level. A fall in nominal wages shifts SRAS right because production becomes cheaper.

A productivity increase shifts SRAS right because firms can produce more output from the same inputs. A negative supply shock, such as a jump in oil prices, shifts SRAS left because costs rise.

Expected future prices matter too. If firms expect higher prices soon, some may hold back output now to sell later, reducing current SRAS.

Students often confuse “higher wages” with “higher price level.” The first shifts SRAS; the second moves along it.

### SRAS compared with LRAS

SRAS is upward sloping because input prices are sticky in the short run. LRAS is vertical because in the long run those input prices adjust.

> **Key Term: long-run aggregate supply (LRAS)**
> The economy’s potential output in the long run, shown as a vertical line because it does not depend on the price level.

In the long run, if the price level rises, nominal wages and other input prices eventually rise too. The temporary profit gain disappears. Firms no longer have a reason to produce more just because the price level is higher. Output returns to its potential level.

That is the major contrast:

- **short run:** sticky wages and sticky input prices -> SRAS upward sloping
- **long run:** flexible wages and input prices -> LRAS vertical

This also explains long-run adjustment in the AD-AS model. If aggregate demand falls and the economy enters a recessionary gap, wages and other resource prices may fall over time. That lowers firms’ costs and shifts SRAS right, helping the economy return to potential output. If aggregate demand rises too much and the economy moves beyond full-employment output, wages and resource prices rise over time, shifting SRAS left and returning output to potential.

So sticky wages explain both why SRAS slopes upward now and why the economy can self-adjust later when wages finally change.

## Key Point Checklist

_This article has covered the following key knowledge points:_

- SRAS is upward sloping because some input prices, especially nominal wages, are sticky in the short run
- When the price level rises but nominal wages do not, firms’ profits increase
- Higher profits give firms an incentive to increase real output supplied
- When the price level falls with sticky wages, profits shrink and firms reduce output supplied
- Real wage is calculated as nominal wage divided by the price level
- A rise in the price level with fixed nominal wages lowers the real wage
- A change in the price level causes a movement along SRAS, not a shift
- Changes in nominal wages, other input costs, productivity, expected future prices, taxes, subsidies, or regulation shift SRAS
- Higher nominal wages or higher resource costs shift SRAS left
- Lower nominal wages or lower resource costs shift SRAS right
- LRAS is vertical because wages and other input prices adjust fully in the long run
- On AP questions, use the phrase “firms increase real output supplied,” not “firms increase aggregate demand”

## Key Terms and Concepts

- short-run aggregate supply (SRAS)
- sticky wages
- nominal wage
- real wage
- input costs
- movement along the SRAS curve
- long-run aggregate supply (LRAS)


Short-Run Aggregate Supply (SRAS) - Sticky prices make SRAS upward