Subjects and lessons to explore.

Law

Economics · Foundations

Inflation

11 min read 5 practice questions
10 key termsSourcesReport an error
Want it in plain words first? Jump to Eli explains — the same idea, no jargon.
On this page 9 sections
  1. In 30 seconds
  2. Why this matters
  3. The college version
  4. Eli explains
  5. Worked example
  6. Key takeaway
  7. Quick check
  8. Study tools
  9. Sources & references

In 30 seconds

is a sustained rise in the general , so each dollar buys a little less than it used to. Economists track it by pricing a fixed basket of goods and services, turning that cost into a like the Consumer Price Index, and reading the as the percentage change in the index. Because prices erode the value of money, inflation makes it essential to separate nominal dollars from real, inflation-adjusted ones when comparing wages, prices, or savings across years.

Why this matters

Inflation quietly rewrites the value of almost every number in the economy. A raise that looks generous can be a pay cut once prices are accounted for; a loan that felt manageable can grow lighter or heavier depending on inflation nobody predicted. Governments and central banks watch the Consumer Price Index because it drives cost-of-living adjustments for Social Security, tax brackets, and wage contracts, and because unexpected inflation quietly transfers wealth between lenders and borrowers. Learning to convert nominal figures to real ones, and to read an inflation rate off a price index, is the difference between understanding what actually happened to your money and being fooled by the dollar sign.

The college version

What inflation is (and is not)

Inflation is a sustained increase in the general price level: on average, across the economy, prices are rising, so the purchasing power of money falls. Two words in that definition do real work. 'General' means the average of many prices, not the price of one good; gasoline getting more expensive while everything else holds steady is a relative price change, not inflation. 'Sustained' means an ongoing trend, not a one-time jump. The inflation rate expresses the trend as a percentage per year. Its mirror image is , a sustained fall in the general price level, when the buying power of money rises instead; the United States saw deflation after the 1920-21 recession and during the Great Depression of the 1930s. A related term, disinflation, means inflation that is still positive but slowing. Because inflation shrinks what a dollar buys, it forces a habit of mind that runs through all of macroeconomics: distinguishing the number of dollars from what those dollars can actually purchase.

Measuring the price level: price indices and the CPI

You cannot average dollars and gallons directly, so economists price a fixed basket of goods and services and track how much that same basket costs over time. To make comparisons clean, they convert the basket's cost into an index number, choosing one period as the and setting its index to 100 by definition. Every other period's index is its basket cost relative to the base. The most cited U.S. measure is the , which the Bureau of Labor Statistics builds from prices in a fixed basket representing the purchases of a typical urban household. BLS collects prices in 75 urban areas from about 23,000 retail and service establishments, weights each item by how much households actually spend on it, and updates those weights every year (annually since January 2023, using a single year of expenditure data; before that, every two years); the standard reference base is 1982-84 = 100. A fixed basket is convenient but imperfect. arises because when one good gets pricier, people buy less of it and switch to substitutes, which a frozen basket ignores, tending to overstate the true rise in the cost of living. Quality and new-goods bias arises because improvements and new products enter the basket only slowly. Economists also watch core inflation, which strips out volatile food and energy prices to reveal the underlying trend.

From index to inflation rate, and nominal versus real

The inflation rate between two periods is the percentage change in the price index: (index now minus index before) divided by index before, times 100. If a price index reads 105.0 one year and 109.2 the next, inflation for that year is (109.2 - 105.0)/105.0 x 100 = 4.0%. This is exactly why nominal and real values differ. A is measured in the dollars of its own year; a is adjusted for inflation so that only changes in purchasing power remain. To deflate a nominal figure into constant base-year dollars, multiply it by the ratio of the base index to the current index (equivalently, divide by current-index/base-index). A worker earning $52,000 when the index is 109.2 has a real income, in dollars of the base year (index 100), of $52,000 x (100/109.2) = $47,619. Comparing that to a base-year salary tells you whether the worker can actually buy more. Note that the CPI is one index among several: the GDP deflator and the Producer Price Index cover different sets of prices and are treated in their own topics.

What causes inflation

Textbooks sort the immediate causes into two families. Demand-pull inflation happens when aggregate demand keeps shifting rightward while the economy is already at or near potential output: firms cannot easily produce more, so the extra spending bids up prices rather than raising quantities. Cost-push inflation happens on the supply side, when a rise in an input price that affects many firms at once, such as oil or labor, shifts short-run aggregate supply leftward, raising the price level even as real output falls. The aggregate demand and supply diagram, though, shows a one-time jump in the price level, not an ongoing trend. Sustained inflation has a deeper source. The quantity equation states that the money supply times the velocity of money equals nominal GDP, which equals the price level times real output. If velocity is roughly stable over the long run, a persistent percentage increase in the money supply produces a matching percentage increase in nominal GDP; once real output is near its potential, that increase shows up as inflation. This is the long-run link between money growth and inflation. How a central bank actually manages the money supply and interest rates to fight inflation is the subject of monetary policy, a neighboring topic.

The costs of inflation, deflation, and hyperinflation

Moderate, steady inflation is a nuisance more than a catastrophe, but it is not free. Menu costs are the real resources spent reprinting price lists and updating systems when prices change often. Shoe-leather costs are the effort people spend economizing on cash, whose value is eroding, by making more frequent trips to the bank or moving money around. The largest effects come from unexpected inflation, which redistributes purchasing power. A lender who agreed to a fixed interest rate is repaid in cheaper dollars, so the borrower gains at the lender's expense; a saver earning 4% when inflation turns out to be 5% earns a real return of about negative 1%; retirees on fixed pensions and workers whose wages lag all lose ground. Inflation also blurs the signals that prices normally send about supply and demand, and when it is high or erratic it adds uncertainty that discourages long-term contracts and investment. At the extreme lies hyperinflation, an outburst of runaway inflation: Russia ran roughly 2,500% per year in the early 1990s, and in Zimbabwe the peak month is estimated at about 79.6 billion percent in mid-November 2008 (Hanke and Kwok, 2009), after which the country abandoned its own currency. Deflation carries its own dangers, since falling prices can lead households to postpone spending and make debts harder to repay.

Eli, the EliExplains learning guide

Eli explains

The same idea, in plain words

Explain it like I’m 10

Inflation means that, on average, prices keep creeping up, so the same ten dollars buys a little less each year. To measure it, people pick a shopping cart full of the usual things a family buys and check the total price of that exact cart every year. They turn the price of the cart into a simple score, calling one year's cart 100. If next year the same cart scores 104, prices rose 4 percent, and that is the inflation rate. Because money loses buying power, a bigger paycheck number is not automatically a raise: if your pay goes up 4 percent but prices go up 9 percent, you can actually buy less than before. That gap between the number of dollars and what they buy is the whole point of inflation.

Picture it like this

Think of your dollars as ice cubes. Inflation is a warm room: leave the cubes out and they slowly shrink, so the pile you saved melts a little every month even though you never spent it. A one-time price jump is like briefly cracking a window, but real inflation is the room staying warm year after year.

Where the picture stops working

Ice melts at a steady, physical rate, but inflation speeds up and slows down with spending, supply shocks, and money creation, and it can even reverse into deflation, which no melting ice cube does. The analogy also pictures money just sitting still; in reality inflation reshuffles wealth between borrowers and lenders rather than simply shrinking everyone's pile by the same amount.

Worked example

Suppose a price index (base year = 100) reads 100.0 in year 1, 105.0 in year 2, and 109.2 in year 3. Year-over-year inflation is (105.0 - 100.0)/100.0 x 100 = 5.0% from year 1 to 2, and (109.2 - 105.0)/105.0 x 100 = 4.0% from year 2 to 3; cumulatively prices rose 9.2% over the two years. Now test a paycheck. A worker earns a nominal $50,000 in year 1 and $52,000 in year 3, a 4.0% raise. To compare fairly, deflate the year-3 salary into year-1 dollars: $52,000 x (100/109.2) = $47,619.05. Even though the nominal number went up, real purchasing power fell about 4.76%, because the 9.2% rise in prices outran the 4.0% raise. All figures were verified by direct calculation.

Key takeaway

Inflation is a sustained rise in the general price level that erodes purchasing power; measure it as the percentage change in a price index such as the CPI, and always convert nominal dollars to real ones before comparing money across years.

Quick check

3 questions here, of 5 in this lesson’s practice set. Answers stay hidden until you check.

Question 1 of 3foundational

Inflation is best defined as:

Choose an answer, then check it.
Question 2 of 3intermediate

The Consumer Price Index is built from a fixed basket of goods and services. Because consumers substitute toward items that become relatively cheaper, this fixed basket tends to:

Choose an answer, then check it.
Question 3 of 3intermediate

A price index rises from 105.0 in one year to 109.2 the next. The inflation rate for that year is closest to:

Choose an answer, then check it.
Practice all 5

Keep learning

Ready to build on this? Continue to the next lesson.

Practice this lesson
Study tools & related lessonsYou’ll learn to · Common mistakes · Easily confused · Key vocabulary · Related

You’ll learn to

  • Define inflation as a sustained rise in the general price level and explain how it erodes purchasing power
  • Explain how a price index is built from a fixed basket and how the Consumer Price Index measures it
  • Compute an inflation rate as the percentage change in a price index between two periods
  • Distinguish nominal from real values and deflate a nominal figure using the CPI
  • Distinguish demand-pull from cost-push inflation and state the long-run link between inflation and money-supply growth
  • Analyze the costs of inflation, including redistribution between lenders and borrowers, and describe deflation and hyperinflation

Common mistakes

  • Calling any price increase 'inflation,' including one good getting more expensive.

    Inflation is a sustained rise in the general (average) price level. One good rising while others hold steady is a relative price change; inflation is about the overall basket.

  • Treating a higher nominal wage or price as automatically 'more.'

    Compare real, inflation-adjusted values. A 4% raise during 9% inflation is a real pay cut, because purchasing power depends on the price level, not the dollar figure.

  • Computing the inflation rate from the base index instead of the previous period's index.

    The inflation rate is the percentage change relative to the prior period: (index now - index before)/index before x 100. Dividing by the base year's 100 every time gives the cumulative change, not the annual rate.

  • Assuming inflation hurts everyone equally.

    Unexpected inflation redistributes: fixed-rate borrowers gain because they repay in cheaper dollars, while fixed-rate lenders and savers lose. Anticipated inflation can be built into contracts and interest rates, blunting the transfer.

  • Believing the CPI perfectly tracks the cost of living.

    A fixed basket has substitution bias and quality/new-goods bias, so it can overstate cost-of-living increases. The CPI is a careful estimate, not an exact measure of every household's experience.

Easily confused

Inflation vs. Deflation

Inflation is a sustained rise in the general price level that erodes the value of money; deflation is a sustained fall in the price level, during which money's buying power increases.

Nominal value vs. Real value

A nominal value is stated in the dollars of its own year; a real value is adjusted with a price index so only changes in purchasing power remain.

Demand-pull inflation vs. Cost-push inflation

Demand-pull comes from aggregate demand rising against an economy near potential, bidding prices up; cost-push comes from economy-wide input costs rising and shifting short-run aggregate supply left, raising prices as output falls.

Key vocabulary

Inflation
A sustained increase in the general (economy-wide) price level, which reduces the purchasing power of money.
Deflation
A sustained decrease in the general price level, during which the buying power of money rises.
Price level
A combined measure of the prices of many goods and services, weighted by how much of each is purchased.
Price index
The cost of a fixed basket of goods and services expressed as an index number, with a chosen base year set equal to 100.
Base year
The reference period whose price index is defined as 100, against which other periods' prices are compared.
Consumer Price Index (CPI)
The Bureau of Labor Statistics measure of the average change over time in the prices a typical urban household pays for a fixed basket of goods and services.
Inflation rate
The percentage change in a price index (or the price level) between two periods.
Nominal value
An amount measured in the current dollars of its own year, unadjusted for inflation.
Real value
An amount adjusted for inflation using a price index, so it reflects purchasing power in constant dollars.
Substitution bias
The tendency of a fixed-basket index to overstate cost-of-living increases because it ignores consumers switching away from goods that become relatively expensive.

Sources & references

  1. Principles of Economics 2e, Section 22.1: Tracking Inflation — OpenStax (Rice University)
  2. Principles of Economics 2e, Section 22.2: How to Measure Changes in the Cost of Living — OpenStax (Rice University)
  3. Principles of Economics 2e, Section 22.3: How the U.S. and Other Countries Experience Inflation — OpenStax (Rice University)
  4. Principles of Economics 2e, Section 22.4: The Confusion Over Inflation — OpenStax (Rice University)
  5. Principles of Economics 2e, Section 24.5: How the AD/AS Model Incorporates Growth, Unemployment, and Inflation — OpenStax (Rice University)
  6. Principles of Economics 2e, Section 28.5: Pitfalls for Monetary Policy — OpenStax (Rice University)
  7. Consumer Price Index: Overview and Frequently Asked Questions — U.S. Bureau of Labor Statistics
  8. On the Measurement of Zimbabwe's Hyperinflation — Cato Journal 29(2) (Steve H. Hanke and Alex K. F. Kwok)

EliExplains lessons are original prose written from the open, credible references above. See Copyright & Licensing.

Researched 2026-08-19

Educational content only. It is not medical, legal or professional advice. Found an error? Tell us.