What is inflation? Definition, causes and worked examples
Inflation is a sustained rise in the general price level of an economy, meaning each unit of currency buys less than before. It is measured as the percentage change in a price index over twelve months – most commonly the Consumer Price Index (CPI). The Bank of England and the Federal Reserve both target 2 % annual inflation. Inflation is not about individual prices rising; it is about the price level as a whole rising.
What does inflation actually mean?
Inflation means the general price level rises over time, so the purchasing power of money falls. The load-bearing word is general. Coffee getting more expensive because a harvest failed is a relative price change, not inflation. Almost everything getting more expensive at once, year after year, is inflation.
One way to hold it: inflation is not really goods becoming worth more, it is money becoming worth less. The same basket costs more units because each unit weighs less. That is why inflation is sometimes described as a tax on cash and on savings that do not earn interest.
How is inflation measured?
Inflation is measured by tracking the price of a fixed basket of goods over time and expressing the change as an index. In the UK the Office for National Statistics collects roughly 180,000 prices each month, weighted by how much of household spending each item represents. In the US the Bureau of Labor Statistics does the equivalent.
Several measures are worth keeping apart:
| Measure | What it is | Used for |
|---|---|---|
| CPI | Consumer Price Index – the standard basket, excluding owner-occupier housing costs | The Bank of England's 2 % target |
| CPIH | CPI including owner-occupiers' housing costs | The ONS's preferred headline measure |
| Core inflation | CPI excluding food and energy | Reading the underlying trend through volatile prices |
| PCE | Personal Consumption Expenditures price index | The Federal Reserve's preferred US measure |
Why several measures? Because food and energy prices swing violently for reasons that have nothing to do with monetary policy. Core inflation strips them out to show whether price pressure is broad-based, which is what a central bank can actually act on. Headline inflation is what households experience; core inflation is what policymakers steer by.
How do you calculate the inflation rate?
The inflation rate is the percentage change in a price index between two points in time:
Inflation (%) = ((Index now − Index then) / Index then) × 100
If CPI stood at 130.0 a year ago and is 133.9 today, the calculation is (133.9 − 130.0) / 130.0 × 100 = 3.0 per cent. The price level has risen 3 per cent over twelve months.
Two traps are worth knowing before an exam. First, inflation can fall while prices keep rising – if inflation drops from 8 to 3 per cent, everything is still getting more expensive, just more slowly. Falling prices require negative inflation, meaning deflation. Second, the base effect: an unusually high index last year mechanically produces a low inflation figure this year, without anything having changed in the economy right now.
What causes inflation?
Textbooks split the causes into three mechanisms, and a real inflationary episode almost always contains all three at once.
Demand-pull inflation occurs when aggregate demand exceeds what the economy can produce – classically described as too much money chasing too few goods. This is the mechanism Milton Friedman (1970) meant with his claim that inflation is always and everywhere a monetary phenomenon: that a permanently higher price level ultimately requires the money supply to have grown faster than output.
Cost-push inflation comes from the supply side when production costs rise – energy, raw materials, wages, import prices through a weaker currency. Firms pass the cost into consumer prices. This is the unpleasant variant, because it raises prices while reducing output at the same time: stagflation.
Expectations are the third and most underrated mechanism. If workers and firms assume 5 per cent inflation next year, wage demands and price lists are set accordingly – and the expectation makes itself true. That is precisely why central banks care so much about the target being seen as credible.
What is the difference between nominal and real?
Nominal means measured in current money; real means adjusted for inflation. The distinction is the single most common error in undergraduate economics exams.
The Fisher relation, after Irving Fisher (1930), gives the rule of thumb: real interest rate ≈ nominal interest rate − inflation. With a savings account paying 4 per cent while inflation runs at 6 per cent, your real return is roughly minus 2 per cent. The balance grows in pounds and shrinks in purchasing power simultaneously. The same applies to pay: a 2 per cent rise during 5 per cent inflation is a real-terms pay cut.
Why does inflation matter to students?
Students are unusually exposed, for three reasons. Income is largely fixed in nominal terms – maintenance loans are uprated on a lag rather than continuously. Spending is concentrated in rent, food and energy, items that weigh heavily in the basket and are hard to postpone. And student debt in the UK is uprated by RPI-linked interest, so a higher inflation reading feeds directly into the balance.
There is a counterweight, though: inflation erodes debts too. A loan fixed in nominal terms becomes worth less in real terms as the price level rises, provided your future income keeps pace with prices.
What are deflation and hyperinflation?
Deflation is the opposite – a sustained fall in the general price level. It sounds welcome and rarely is: if households expect lower prices they postpone purchases, demand falls, and debt burdens grow in real terms because the loan amount is fixed in nominal terms. Japan's long episode from the 1990s is the standard textbook case.
Hyperinflation is the extreme opposite, conventionally defined after Philip Cagan (1956) as inflation exceeding 50 per cent per month. Weimar Germany in 1923 and Zimbabwe in 2008 are the usual examples. What virtually every case shares is a government financing deficits by printing money, followed by confidence in the currency collapsing faster than the presses could run.
How to actually learn this for the exam
Inflation is one of those concepts that feels obvious while reading and evaporates when you have to explain it. Test yourself instead of rereading: can you explain the difference between headline and core inflation without looking, and calculate a real interest rate from two numbers? If so, you know it.
That is exactly the check flashcards built from your own course material are for. Memmo schedules the review with FSRS – the same algorithm family Anki moved to – so each concept comes back just before you would have forgotten it. More on why that works in our guide to spaced repetition.
Frequently asked questions
What is inflation in simple terms?
Inflation is when the prices of most things rise at the same time, so money becomes worth less. At 3 per cent inflation, something that cost £100 last year costs £103 now. Your income therefore buys less than it did, unless it rose by as much.
What is the difference between headline and core inflation?
Headline inflation covers the whole basket, including food and energy. Core inflation strips those two out because they swing sharply for reasons unrelated to monetary policy. Headline is what households actually feel; core is what central banks watch to judge whether price pressure is broad-based.
Why is the inflation target 2 per cent?
Two per cent is low enough that the price level stays predictable, but far enough above zero to leave a margin against deflation and room to cut interest rates in a downturn. The figure is an international convention rather than a derived optimum – most advanced-economy central banks use the same number.
Is inflation always bad?
No. Low, stable inflation is treated as a sign of a functioning economy and gives the central bank room to act. The problems come when inflation is high, volatile or unexpected – purchasing power is then redistributed arbitrarily between borrowers and savers, and long-term planning becomes difficult.