In simple terms
A friendly intro before the formal notes — no formulas yet.
Keeping money's value steady
Inflation is when the general price level keeps rising, so each unit of money buys less over time. Governments and central banks want inflation to be low AND stable — usually around 2% — because both fast-rising prices and falling prices do real economic damage.
Think of money as a ruler used to measure value. If the ruler keeps shrinking (inflation), every price tag, wage and contract becomes harder to trust, and planning gets messy. If the ruler suddenly grows (deflation), people postpone spending and the economy stalls. A ruler that changes length slowly and predictably lets everyone plan with confidence.
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Learn the three terms: inflation (the price level is rising), disinflation (it is still rising but more slowly) and deflation (the price level is actually falling).
- 2
Understand measurement: a Consumer Price Index tracks the price of a weighted basket of goods a typical household buys, and the inflation rate is the percentage change in that index.
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Diagnose the cause: demand-pull inflation comes from rising aggregate demand; cost-push inflation comes from rising costs that shift short-run aggregate supply left.
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Weigh the consequences: high inflation erodes purchasing power and creates uncertainty, while deflation can trap an economy in falling demand and rising real debt — which is why price stability is a policy goal.
Explore the concept
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Key formulas
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Full topic notes
Formal explanation with the rigour you need for the exam.
Defining inflation, disinflation and deflation
The general price level is the average of prices across an economy. Inflation is a sustained rise in that level: money loses purchasing power, so each pound, dollar or euro buys less than before. Deflation is the opposite — a sustained fall in the general price level, i.e. a negative inflation rate. Between them sits a term students most often get wrong: disinflation, which means the rate of inflation is falling but is still positive. Under disinflation prices are still rising; they are just rising more slowly.
Inflation — the price level is rising (positive inflation rate, e.g. +4%).
Disinflation — the price level is still rising, but the RATE is falling (e.g. inflation slowing from 5% to 3%). This is a fall in the rate, not in prices.
Deflation — the price level is actually FALLING (a negative inflation rate, e.g. −1%).
The single most common error here is treating disinflation and deflation as the same thing. They are not: only deflation involves prices falling.
Measuring inflation — the Consumer Price Index (CPI)
Inflation is measured by tracking the price of a basket of goods and services that a typical household buys. Prices are collected regularly and combined into a Consumer Price Index (CPI). The basket is weighted: each category is given a weight equal to its share of household spending, so a price change in a large item such as housing affects the index far more than the same percentage change in a minor item. One year is chosen as the base year and its index is set to 100; the index in any other year then shows how prices compare with that base. The rate of inflation is the percentage change in the index from one period to the next.
Constructing a weighted price index
Because a household spends different amounts on different categories, the CPI multiplies each category's price index by its spending weight, sums the results, and divides by the total weight. This 'weighted average' is what makes the CPI reflect the price change an average household actually experiences, rather than a simple average of unrelated price tags.
The limitations of CPI
The CPI is the standard measure of inflation, but it is an estimate, and examiners reward students who can evaluate its weaknesses rather than treat it as perfect.
The basket is fixed for a period — but spending habits change continuously, so a basket updated only occasionally can misrepresent what households actually buy today.
New products enter slowly — innovative goods (and the price falls that often follow their launch) may not appear in the basket for some time, so genuine cost-of-living changes are missed.
Quality changes are hard to strip out — if a phone costs more but is far better, part of the 'price rise' is really improved quality, not pure inflation; separating the two is difficult.
It is a single national average — one figure hides very different experiences. Households whose spending is concentrated in fast-rising categories (e.g. energy or rent) face higher effective inflation than the headline rate suggests.
Substitution is ignored — when one good rises in price, consumers switch to cheaper alternatives, but a fixed basket does not capture this, tending to overstate the true rise in the cost of living.
The causes of inflation: demand-pull and cost-push
Inflation has two broad causes, best shown on an AD/AS diagram. Demand-pull inflation originates on the demand side: a rise in aggregate demand pulls the price level up. Cost-push inflation originates on the supply side: rising costs of production shift short-run aggregate supply to the left, pushing the price level up. Diagnosing which is at work matters, because the two have different side effects and call for different policy responses.
Demand-pull inflation — an increase in any component of AD (consumption, investment, government spending or net exports) shifts AD right. Along an upward-sloping AS curve, this raises both the price level and real output. It typically occurs when an economy is near full capacity, where extra demand mostly bids up prices rather than raising output.
Cost-push inflation — a rise in production costs (higher wages, more expensive imported raw materials, higher energy prices, or a depreciating currency raising import costs) shifts SRAS left. This raises the price level while real output FALLS — the uncomfortable combination of rising prices and rising unemployment known as stagflation.
The key contrast: demand-pull raises prices AND output together; cost-push raises prices while output falls. On a diagram, demand-pull is a rightward shift of AD; cost-push is a leftward shift of SRAS.
The consequences of high inflation and of deflation
Both high inflation and deflation impose real costs, which is why the objective is low and STABLE inflation rather than zero.
Costs of high inflation:
- Loss of purchasing power — if incomes rise more slowly than prices, real incomes and living standards fall, hitting people on fixed incomes hardest.
- Uncertainty and lower investment — when future prices and costs are hard to predict, firms delay investment and long-term planning, weakening growth.
- Redistribution — inflation erodes the real value of savings (hurting savers and lenders) while reducing the real value of debt (benefiting borrowers), redistributing wealth arbitrarily.
- Menu and shoe-leather costs — firms bear the cost of constantly changing prices, and households waste time and effort trying to protect the value of their money.
- Loss of international competitiveness — if inflation is higher than in trading partners, exports become relatively expensive and imports cheaper, worsening the trade balance.
Costs of deflation:
- Deferred consumption — expecting prices to fall further, households postpone purchases, cutting aggregate demand.
- Rising real value of debt — as prices and incomes fall, fixed debts become harder to repay, raising defaults for households and firms.
- Deflationary spiral — falling demand leads to lower prices and wages, which cut demand further, entrenching recession.
- Rising unemployment — as revenues and profits fall, firms cut output and lay off workers, and interest-rate policy loses traction near zero.
When evaluating the effects of inflation, always identify the stakeholders — savers versus borrowers, workers on fixed versus flexible incomes, exporters, and the government as a debtor. Top answers also stress that the RATE and the STABILITY of inflation matter more than its mere existence: moderate, predictable inflation of around 2% is a policy goal, whereas high or volatile inflation is the genuine problem.
Why price stability is a macroeconomic objective
Because both high inflation and deflation are damaging, governments and central banks pursue price stability — usually defined as low, positive and predictable inflation, commonly around a 2% target. Stable prices preserve the value of money as a unit of account, so wages, contracts and investment decisions can be planned with confidence. A small positive target also keeps a safety margin above deflation, allows real wages to adjust without cash pay cuts, and offsets the CPI's tendency to slightly overstate true inflation. Price stability is therefore not an end in itself but a foundation for the other macro goals — sustained growth, low unemployment and external balance — because it protects the reliability of the price signals on which the whole economy depends.
Common mistakes examiners penalise
Confusing disinflation with deflation — disinflation means the inflation rate is falling but still positive (prices rising more slowly); deflation means the price level is actually falling (a negative rate). Only deflation involves falling prices.
Dividing by the wrong base when calculating inflation — the percentage change divides by the ORIGINAL (earlier) index, not the new one. Dividing by the current index is a conceptual error that loses the method mark.
Quoting the change in the index instead of the percentage change — a rise from 125 to 131 is a 6-point change but a 4.8% inflation rate. The inflation rate is always the PERCENTAGE change in the index.
Treating the CPI as a simple (unweighted) average — it is weighted by spending shares, so a large category's price change moves the index more than a small category's.
Mixing up demand-pull and cost-push — demand-pull shifts AD right and raises prices AND output; cost-push shifts SRAS left and raises prices while output FALLS. Naming the wrong shift on the diagram costs marks.
Assuming all inflation is bad and all deflation is worse — the objective is low, stable, positive inflation (about 2%), not zero. Whether deflation harms depends on whether it comes from collapsing demand ('bad') or from rising supply/productivity ('good').
Worked examples
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A country's consumer price index rises from 125 in year 1 to 131 in year 2. Calculate the rate of inflation between year 1 and year 2. [2]
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Model answer
A simplified economy divides household spending into three categories. The table shows each category's weight (its share of spending, out of 100) and its price index for the current year (base year = 100 for every category).
| Category | Weight | Price index (current year) |
|---|---|---|
| Food | 40 | 110 |
| --- | --- | --- |
| Housing | 35 | 105 |
| Transport | 25 | 120 |
(a) Calculate the weighted CPI for the current year. [3] (b) State the overall rate of inflation since the base year. [1]
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Model answer
An economy is operating close to full employment. The government sharply increases spending and cuts taxes, and consumer and business confidence is high. Using an AD/AS diagram, explain the type of inflation this is likely to cause. [4]
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Model answer
How it all connects
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Glossary
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Quick check
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Revision flashcards
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Inflation
A sustained increase in the general (average) price level of an economy over time, which reduces the purchasing power of money.
Key takeaways
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- ✓
Inflation — the price level is rising (positive inflation rate, e.g. +4%).
- ✓
Disinflation — the price level is still rising, but the RATE is falling (e.g. inflation slowing from 5% to 3%). This is a fall in the rate, not in prices.
- ✓
Deflation — the price level is actually FALLING (a negative inflation rate, e.g. −1%).
- ✓
The single most common error here is treating disinflation and deflation as the same thing. They are not: only deflation involves prices falling.
Practice — then mark it
The whole point: a real Cambridge question, marked mark-by-mark.
Practise a Paper 3 inflation calculation and get it marked on the POINTS scheme
Practise a Paper 3 inflation calculation and get it marked on the POINTS scheme
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Checkpoint
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