What Causes Inflation? Demand-Pull, Cost-Push, and How It Is Measured

Inflation is a sustained rise in the general price level of goods and services, and it has two main causes: demand-pull inflation, where total spending outpaces what the economy can produce, and cost-push inflation, where rising production costs shrink supply. On the AP Macro exam you also need to explain the monetary root of inflation through the quantity theory of money, know how the Consumer Price Index (CPI) and the GDP deflator measure it, distinguish real from nominal values, and list who wins and who loses when prices rise.

This guide walks through each cause, the measurement tools, and the costs, with the graph mechanics and formulas you will be tested on. To see the price-level shifts described here in motion, open the AD-AS sandbox and follow along.

Demand-Pull Inflation: Too Much Spending

Demand-pull inflation happens when aggregate demand grows faster than the economy's capacity to produce, so buyers bid up prices. The classic phrase is "too much money chasing too few goods." On the aggregate demand and aggregate supply (AD-AS) model, this shows up as the AD curve shifting right, moving the equilibrium up along the upward-sloping short-run aggregate supply curve. The result is a higher price level and higher real GDP in the short run.

Common triggers of a rightward AD shift include tax cuts, increased government spending, rising consumer confidence, a growing money supply, or stronger exports. Because AD is the sum of consumption, investment, government spending, and net exports, anything that raises one of those components can pull prices up. Demand-pull inflation is often associated with a booming economy operating near or beyond full employment, where an inflationary gap opens up as real GDP exceeds potential output.

You can watch the AD curve shift and the equilibrium move up along the SRAS curve in the AD-AS sandbox. Notice that the closer the economy is to full employment, the steeper the SRAS curve becomes, so the same AD shift produces more inflation and less added output.

Cost-Push Inflation: Rising Production Costs

Cost-push inflation occurs when the cost of producing goods rises, pushing the short-run aggregate supply curve to the left. Producers pass higher input costs on to consumers as higher prices. On the AD-AS model, a leftward SRAS shift raises the price level while lowering real GDP, an uncomfortable combination that produces stagflation, meaning stagnant output plus inflation.

The usual causes are supply shocks such as a spike in oil or energy prices, a jump in nominal wages, higher taxes on producers, natural disasters, or disrupted supply chains. The 1970s oil embargoes are the textbook example: energy costs surged, SRAS shifted left, and the United States experienced simultaneous high inflation and high unemployment. Cost-push inflation is harder for policymakers to fix, because the tools that fight inflation (cutting AD) tend to deepen the output loss, while the tools that boost output tend to worsen the inflation.

The key contrast is the source of the price increase: demand-pull comes from stronger spending, cost-push comes from a shrinking supply. The two also differ in what happens to real GDP, which is the tell examiners look for.

The Quantity Theory of Money

Over the long run, most economists trace persistent inflation to growth in the money supply. The quantity theory of money is built on the equation of exchange: M times V equals P times Y. Here M is the money supply, V is the velocity of money (how many times each dollar is spent per year), P is the price level, and Y is real output.

The theory assumes velocity (V) is roughly constant and, at full employment, real output (Y) is fixed by the economy's productive capacity. Under those assumptions, any increase in M shows up as a roughly proportional increase in P. In other words, if the central bank doubles the money supply while output stays fixed and velocity is stable, the price level doubles. This is why economists like Milton Friedman argued that "inflation is always and everywhere a monetary phenomenon." Countries that print money rapidly to fund government spending, such as Weimar Germany or Zimbabwe, tend to experience hyperinflation.

The link between money and prices runs through aggregate demand: more money in the economy lowers interest rates, boosts borrowing and spending, and shifts AD right, which is the demand-pull channel above. You can trace how the central bank changes the money supply and interest rates in the monetary policy sandbox, and read short definitions of these terms in the glossary.

How Inflation Is Measured: CPI and the GDP Deflator

To measure inflation you need a price index, a number that tracks the cost of a set of goods over time. The two big ones in AP Macro are the CPI and the GDP deflator.

The Consumer Price Index (CPI) tracks the price of a fixed basket of goods and services bought by a typical urban household. The formula is CPI equals the cost of the basket in the current year divided by the cost of the same basket in the base year, times 100. The base year always has a CPI of 100, because its cost is divided by itself. Because the basket is fixed and includes imported goods, the CPI is the standard gauge of how inflation hits everyday consumers. Our CPI calculator walks through the basket math step by step.

The GDP deflator measures the price of all new, domestically produced final goods and services, not just consumer goods. It equals nominal GDP divided by real GDP, times 100. Unlike the CPI, the deflator excludes imports, includes business investment and government purchases, and updates its basket with current production rather than holding it fixed.

Once you have a price index, the inflation rate is the percentage change in the index between two years. The formula is the current-year index minus the previous-year index, divided by the previous-year index, times 100. So if CPI rises from 200 to 210, inflation is (210 minus 200) divided by 200, times 100, which equals 5 percent. Practice this in the inflation-rate calculator.

One caveat the exam likes: because the CPI holds its basket fixed, it suffers from substitution bias and tends to slightly overstate the true cost of living, since consumers switch away from goods whose prices rise fastest.

Real vs. Nominal Values

Whenever prices are changing, you must separate nominal values (measured in current dollars) from real values (adjusted for inflation). A nominal figure tells you the sticker number; a real figure tells you actual purchasing power. To convert, divide the nominal value by the price index and multiply by 100 (this assumes the index is on a base-year-equals-100 scale, like the CPI and deflator above), or more simply, real growth roughly equals nominal growth minus the inflation rate.

The same idea applies to interest rates. The real interest rate equals the nominal interest rate minus the inflation rate, a relationship known as the Fisher equation. If your savings account pays 4 percent nominal interest but inflation is 3 percent, your real return is only 1 percent. This distinction is central to understanding who gains and loses from inflation, and it appears constantly in the loanable funds market.

The Costs of Inflation

Even moderate, predictable inflation carries real costs, and unexpected inflation is worse. The main costs tested in AP Macro are:

• Menu costs: the expense firms bear when they physically change prices, such as reprinting menus, updating price tags, and reissuing catalogs. These grow as inflation forces more frequent price changes.
• Shoe-leather costs: the time and effort people waste trying to hold less cash when prices rise, making extra trips to the bank because higher inflation raises the nominal interest rate, making idle cash more costly to hold. The name evokes wearing out your shoes running to the bank.
• Redistribution between borrowers and lenders: unexpected inflation helps borrowers, who repay loans in cheaper dollars, and hurts lenders, who are paid back in money worth less than they lent. Savers and people on fixed incomes lose purchasing power.
• Reduced purchasing power: if nominal wages do not keep pace with prices, real wages fall and living standards drop.
• Uncertainty: volatile inflation makes it hard for businesses to plan investment and for households to plan saving, which can slow long-run growth.

These costs are usually small when inflation is low and stable, which is why the Federal Reserve targets a low positive rate rather than zero. They become severe during hyperinflation, generally defined as inflation above 50 percent per month, when money can lose its role as a store of value entirely.

Putting It Together

Inflation on the AP exam is a story about three linked pieces: a cause (demand-pull or cost-push, both traceable to money growth in the long run), a measurement (CPI or the GDP deflator feeding an inflation-rate calculation), and a set of costs (menu, shoe-leather, and redistribution effects). If you can draw the correct AD-AS shift, plug numbers into the CPI and inflation-rate formulas, and explain who wins and loses, you have covered nearly every way the topic shows up in multiple-choice and free-response questions.

Build fluency by practicing the graph shifts in the AD-AS sandbox and reviewing the broader unit on the macroeconomics hub. Then test your recall with the inflation-rate calculator and skim related terms in the glossary.