Economic Growth

AP Macroeconomics· AP Macroeconomics CED — Long-Run Consequences of Stabilization Policies· 14 min read

1. What Is Economic Growth?★☆☆☆☆⏱ 3 min

Economic growth is defined as a sustained increase in an economy's potential real output (real GDP) over time. For measuring changes in average living standards, economists use real GDP per capita growth, which adjusts total GDP growth for changes in population size.

This differs from short-run "cyclical growth," which is just an increase in actual output as an economy recovers from a recession toward its existing potential output. Long-run economic growth, the core concept tested in AP Macroeconomics Unit 5, represents an increase in potential output itself, shifting the long-run aggregate supply (LRAS) curve to the right.

📘 Definition

Long-Run Economic Growth

A sustained increase in an economy's potential real GDP over time, represented by a rightward shift of the LRAS curve

Example:

A 2% annual increase in potential real GDP per capita over 20 years

Economic growth concepts make up 15-20% of the overall AP exam score. You can expect 3-5 multiple-choice questions on this topic, and it is often the core theme of a 10-point long free-response question.

2. The Rule of 70★★☆☆☆⏱ 4 min

The Rule of 70 is a simple approximation to calculate how long it takes a variable growing at a constant annual rate to double in value. It is most commonly used for comparing how fast different economies grow their GDP per capita, but it can also be applied to inflation, population, or any other compounding variable.

\text{Doubling Time (years)} \approx \frac{70}{g}

Where $g$ is the annual growth rate of the variable, measured in percentage points. The approximation comes from the math of continuous compounding, and is very accurate for growth rates between 0.1% and 10%, which covers almost all cases you will see on the AP exam.

📐 Worked Example

Country X has a real GDP per capita growing at 2.5% annually. Country Y has a real GDP per capita growing at 1.4% annually. If both start with a real GDP per capita of $15,000, what is the approximate difference in their per capita GDP after 70 years?

1
Apply the Rule of 70 to find each country's doubling time
2
$\text{Doubling time}_X = \frac{70}{2.5} = 28 \text{ years}, \quad \text{Doubling time}_Y = \frac{70}{1.4} = 50 \text{ years}$
3
Calculate how many times each country doubles its GDP over 70 years
4
$\text{X}: \frac{70}{28} = 2.5 \text{ doublings}, \quad \text{Y}: \frac{70}{50} = 1.4 \text{ doublings}$
5
Calculate final per capita GDP for each country
6
$\text{X}: 15000 * 2^{2.5} \approx \$84,840, \quad \text{Y}: 15000 * 2^{1.4} \approx \$39,585$
7
Find the difference between the two final values
8
$84840 - 39585 = \$45,255$

Exam tip:

Always confirm the growth rate is entered in percentage points (e.g., 2.5 for 2.5% growth), not decimal form (0.025). Entering decimals will give a doubling time 100 times too large, which is one of the most common tested mistakes.

3. Growth Accounting with the Aggregate Production Function★★★☆☆⏱ 4 min

Growth accounting is a method to break down total economic growth into contributions from different sources: input accumulation (more labor, more capital) and productivity growth (better technology, better institutions). The standard aggregate production function used in AP Macroeconomics is the Cobb-Douglas form:

Y = A * K^\alpha * L^{1-\alpha}

Where $Y$ = total real output, $A$ = total factor productivity (TFP, which captures technology, human capital, and institutional quality), $K$ = physical capital stock, $L$ = labor input, and $α$ = the share of national income that goes to owners of capital (usually 0.3 to 0.4 in most developed economies).

To get the growth accounting formula, take the percentage change of both sides, which simplifies to:

\%\Delta Y = \%\Delta A + \alpha(\%\Delta K) + (1-\alpha)(\%\Delta L)

📐 Worked Example

A developing economy has a capital share of income $α = 0.35$ . Over the last decade, total real GDP grew at 4.5% annually, the capital stock grew at 5% annually, and the labor force grew at 2% annually. What share of total annual growth comes from total factor productivity?

1
Write the growth accounting formula
2
$\%\Delta Y = \%\Delta A + \alpha(\%\Delta K) + (1-\alpha)(\%\Delta L)$
3
Rearrange to isolate the unknown TFP growth
4
$\%\Delta A = \%\Delta Y - \alpha(\%\Delta K) - (1-\alpha)(\%\Delta L)$
5
Plug in the given values
6
$\%\Delta A = 4.5 - (0.35*5) - (0.65*2) = 1.45\%$
7
TFP contributes 1.45 percentage points of the 4.5% total growth, which is roughly 32% of total annual growth

Exam tip:

On FRQs, always write out the full formula before plugging in values. Partial credit is almost always awarded for the correct formula setup even if your final calculation is wrong.

4. Long-Run Effects of Stabilization Policy on Growth★★★☆☆⏱ 3 min

Stabilization policies (fiscal and monetary policies used to smooth short-run business cycles) have long-run consequences for economic growth, which is the core focus of this unit. The effect on growth depends on the type of policy and how it is implemented:

Expansionary fiscal policy: Deficit-funded stimulus raises interest rates and crowds out private investment, slowing long-run growth. If the deficit funds productive public investment (infrastructure, education, R&D), it increases TFP and crowds in private investment, accelerating growth.
Expansionary monetary policy: Money is neutral in the long run: permanent money supply increases only raise prices, not potential output. Low, stable inflation reduces uncertainty and encourages investment, while permanently high inflation reduces growth.
Supply-side fiscal policy: Policies like investment tax credits, lower capital gains taxes, and deregulation increase incentives for saving and investment, accelerating capital accumulation and TFP growth.

📐 Worked Example

A government responds to a recession with a $300 billion deficit-financed stimulus package: 60% of the deficit funds renewable energy infrastructure, and 40% goes to household transfer payments. How does this policy affect long-run economic growth compared to a deficit of the same size that funds only transfer payments?

1
Deficit spending on public infrastructure increases public capital stock, which raises total factor productivity $A$ in the aggregate production function. Transfer payments do not increase productive capital.
2
The productivity gain from infrastructure raises the marginal product of private capital, making private investment more attractive than in the all-transfer case. This offsets crowding out from higher deficits.
3
Higher $A$ and higher net capital accumulation means potential output is higher in the long run, so the LRAS curve shifts further right than it would in the all-transfer case.
4
This policy leads to faster long-run economic growth than an equal-sized deficit spent only on transfers.

Exam tip:

Never assume all expansionary fiscal policy reduces long-run growth. Always check what the deficit spending is used for before concluding the effect on growth.

5. AP-Style Concept Check★★★★☆⏱ 4 min

✓ Quick check

Test your understanding with this AP-style multiple choice question:

A country has a constant annual growth rate of real GDP per capita of 1.4%. Its population is growing at 1.1% annually. What is the approximate doubling time of the country's total real GDP?
- 28 years
- 35 years
- 50 years
- 64 years
Reveal answer
28 years —
Correct: Total real GDP growth = per capita growth + population growth = 1.4% + 1.1% = 2.5%. Doubling time = 70 / 2.5 = 28 years.

📐 Worked Example

The country of Graecia has an aggregate production function $Y = A K^{0.4} L^{0.6}$ . Over the past decade, Graecia has had 3.2% annual total real GDP growth, 3% annual growth in the capital stock, and 1% annual growth in the labor force. (a) Calculate annual TFP growth. (b) An investment tax credit increases capital growth by 1 percentage point. What is the new total output growth rate? (c) Will permanently raising the inflation target from 2% to 4% increase long-run growth? Use long-run monetary neutrality to explain.

1
Part (a): Rearrange the growth accounting formula to solve for TFP growth:
2
$\%\Delta A = 3.2 - (0.4)(3) - (0.6)(1) = 1.4\%$
3
Part (b): A 1 percentage point increase in capital growth adds $α * 1% = 0.4%$ to total growth:
4
$\text{New total growth} = 3.2\% + 0.4\% = 3.6\%$
5
Investment tax credits increase capital accumulation, which directly adds to output growth per the growth accounting formula.
6
Part (c): No, this policy will not permanently increase long-run growth. Long-run monetary neutrality states that changes in the steady inflation rate only affect nominal variables like prices and wages, not real variables like potential output or long-run real growth. High inflation also increases uncertainty, which typically discourages investment and reduces long-run growth.

6. Common Pitfalls

Wrong move:

Using the growth rate in decimal form (e.g., 0.02 for 2%) in the Rule of 70, getting a doubling time of 350 years instead of 35

Why:

Students confuse percentage growth rates with the decimal form used in standard compound interest formulas

Correct move:

Always confirm your growth rate is in percentage points before plugging into the Rule of 70 formula

Wrong move:

Confusing short-run increases in real GDP (recovery from recession) with long-run economic growth

Why:

Both increase measured real GDP, so students mix up the two concepts on exam questions

Correct move:

Always ask: Is this movement of actual output toward existing potential output, or is potential output itself increasing? Only the latter counts as long-run growth

Wrong move:

Assuming all expansionary fiscal policy reduces long-run economic growth via crowding out

Why:

Students learn the crowding out effect and generalize it to all deficit spending, regardless of its purpose

Correct move:

Always check if the deficit is spent on productive public investment; that investment increases potential output, leading to faster not slower growth

Wrong move:

Forgetting to weight input growth by income share in growth accounting, adding growth rates directly instead

Why:

Students confuse the size of inputs with their output elasticity when calculating growth contributions

Correct move:

Always multiply each input's growth rate by its share of national income before adding up, then subtract from total growth to get TFP growth

Wrong move:

Claiming expansionary monetary policy permanently increases long-run economic growth

Why:

Students see that low nominal rates increase investment in the short run, and forget the long-run neutrality of money

Correct move:

State that monetary policy only affects long-run growth if it delivers low, stable inflation that encourages investment; permanently expansionary policy only raises inflation, not real growth

Wrong move:

Using total real GDP growth to measure changes in the average standard of living

Why:

Students forget that population growth erodes gains in total GDP

Correct move:

If the question asks about standard of living, always use real GDP per capita growth, calculated as total GDP growth minus population growth

7. Quick Reference Cheatsheet

Category	Formula / Concept	Notes
Long-Run Economic Growth	Sustained increase in potential real GDP	Rightward shift of LRAS; only potential output increases count, not short-run recovery
Rule of 70	$Doubling Time \approx \frac{70}{g}$	$g$ = annual growth rate in percentage points; works for any compounding variable
Real GDP per Capita Growth	$%Δ y = %Δ Y - %Δ Population$	Correct measure for changes in average standard of living
Cobb-Douglas Production Function	$Y = A K^{α} L^{1 - α}$	$A$ =TFP, $K$ =capital, $L$ =labor, $α$ =capital's share of income
Growth Accounting Formula	$%Δ Y = %Δ A + α (%Δ K) + (1 - α) (%Δ L)$	Breaks total growth into productivity, capital, and labor contributions
Crowding Out	Higher deficits → higher interest rates → lower private investment	Reduces long-run capital accumulation and growth
Crowding In	Productive public investment → higher private productivity → higher private investment	Increases long-run TFP and growth
Long-Run Monetary Neutrality	Changes in money supply do not change long-run real growth	Permanent expansionary policy only increases inflation, not real output

When this came up on past exams

AI-estimated based on syllabus patterns — cross-check with official past papers for accuracy. Use only as revision-focus signals.

2023 · AP Macro MCQ
Rule of 70 doubling time calculation
2022 · AP Macro FRQ
Growth accounting and policy analysis

Going deeper

Official SyllabusAP Macroeconomics CED

What's Next

This topic builds the foundation for analyzing how short-run policy choices shape the long-run trajectory of the economy, which is the core theme of AP Macroeconomics Unit 5. Next, you will apply the concepts of growth and productivity to analyze catch-up growth between developing and developed economies, and how institutional factors affect long-run growth outcomes. Without mastering how to calculate growth rates and how policies shift LRAS, you will not be able to correctly answer cross-country growth comparison questions that are common on the AP exam. This topic also connects to the broader course theme of the short-run vs long-run policy trade-off, which appears frequently on FRQs across the exam.