In short: Inflation measures the ongoing change in consumer prices paid by households for everyday goods and services. When prices rise, an unchanged sum of cash buys fewer goods over time, eroding purchasing power. Slower inflation (disinflation) means prices continue to increase at a reduced pace, whereas price drops (deflation) are rare. Over decades, preserving purchasing power requires returns that match or exceed price increases.
What inflation is: official definitions
In public discussions, inflation is frequently described as money losing value. Statistical agencies define it through observed consumer prices: inflation is the change over time in the prices households pay for consumer goods and services.
Headline inflation percentages are annual rates of change: the price change of consumer goods and services between the current month and the same month a year earlier. A reading of 2.0% means that the measured basket costs 2.0% more than twelve months earlier.
In the United States, the Bureau of Labor Statistics (BLS) uses an equivalent conceptual framework for its Consumer Price Index: “the CPI measures the average change in price over time of a market basket of consumer goods and services.”
Statistical institutions emphasize two important boundaries regarding consumer price indices:
- The index is a statistical average: As the BLS notes, “The CPI does not necessarily measure your own experience with price change.” Individual household spending patterns differ substantially from national weights.
- Investment items are excluded: The BLS explicitly states that “The CPI also does not include investment items, such as stocks, bonds, real estate, and life insurance”. The index reflects consumption expenditure rather than asset accumulation.
For savers, this distinction is fundamental: a consumer price index describes historical price movements across a representative consumer basket, not the performance of an investment portfolio or a bank savings account.
How inflation is measured: CPI versus HICP
The euro area measures inflation with the Harmonised Index of Consumer Prices (HICP), produced by Eurostat, which is built to be comparable across countries. The United States uses its own Consumer Price Index.
National consumer price indices can differ from the HICP in scope. One example is housing: the HICP does not include the costs of owning a home. Because of such differences, a national headline figure can differ from the HICP figure for the same month.
When tracking inflation trends, differentiating between two closely related terms is essential:
- Disinflation: A reduction in the rate of inflation. For instance, when euro area annual HICP inflation slowed from 10.6% in October 2022 to 2.4% in November 2023, the pace of price increases decelerated significantly. However, because the rate remained positive, consumer prices were still higher than the year before. Disinflation does not mean prices fell.
- Deflation: A negative annual inflation rate, meaning the general price level of the consumer basket decreased over twelve months. Brief negative annual rates have occurred in the euro area, for example in 2009 and early 2015.
What inflation does to a fixed cash sum
When money remains in an account that earns zero interest, its nominal value stays unchanged. A bank balance of €10,000 remains exactly €10,000 on your account statement year after year. However, if consumer prices increase over time, each euro buys a smaller volume of goods and services.
To examine this effect mathematically, we apply the formula used by the Stazora purchasing power calculator. The purchasing power of a fixed amount after a given number of years at an annual inflation rate is calculated as:
Purchasing Power = Initial Amount ÷ (1 + Inflation Rate)^Years
The table below models a starting capital of €10,000 kept in cash without nominal interest (0% nominal return), without additional deposits or withdrawals, across two illustrative inflation assumptions: a steady 2.0% annual rate (reflecting the ECB’s medium-term price stability target) and a 3.0% annual rate (reflecting moderate elevated inflation). All figures are computed directly by the site’s calculation engine.
| Horizon | Nominal balance | Purchasing power (2.0% inflation) | Purchasing power lost (2.0%) | Purchasing power (3.0% inflation) | Purchasing power lost (3.0%) |
|---|---|---|---|---|---|
| 10 years | €10,000 | €8,203 | 18.0% | €7,441 | 25.6% |
| 20 years | €10,000 | €6,730 | 32.7% | €5,537 | 44.6% |
| 30 years | €10,000 | €5,521 | 44.8% | €4,120 | 58.8% |
At an annual inflation rate of 2.0%, after 10 years, an unchanged sum of €10,000 has the purchasing power of €8,203 in base-year prices. To buy the basket of goods that €10,000 bought at the start, you would need €12,190 after 10 years, €14,859 after 20 years, and €18,114 after 30 years. Over 30 years at 2.0% inflation, nearly 45% of the initial purchasing power disappears, even though the nominal euro balance never dropped by a single cent.
Investing involves risk of loss. The figures presented by this calculator are for illustrative purposes only and do not constitute financial advice. Past performance does not guarantee future results.
Nominal return versus real return
Understanding inflation is essential for interpreting investment results. Financial returns are evaluated in two distinct ways:
- Nominal return: The percentage increase in currency units, without adjusting for changes in purchasing power. If a savings account yields 2.5% in a year, the nominal return is 2.5%.
- Real return: The percentage increase in purchasing power after adjusting for the rate of inflation over the period.
In financial mathematics, the exact relationship between nominal return, real return, and inflation is expressed through the Fisher equation:
1 + Real Return = (1 + Nominal Return) ÷ (1 + Inflation Rate)
For modest rates, the real return can be approximated by subtracting the inflation rate from the nominal return (Real Return ≈ Nominal Return − Inflation Rate). For instance, if an account earns 1.5% nominal interest while consumer price inflation is 3.0%, the real return is negative at approximately -1.5% (exact Fisher calculation: -1.46%). In that scenario, despite earning interest in nominal euros, the account holder experiences a net loss of purchasing power.
This dynamic is why some long-term savers look at diversified equity index funds (ETFs). Equity investments can rise or fall in value, and a return above inflation is not assured over any fixed timeframe, unlike a bank balance whose nominal value does not drop. See volatility.
This is general information, not tax or investment advice. For your own situation, consult a qualified tax adviser, a financial adviser licensed by the AFM (the Dutch financial markets authority) or the Belastingdienst.
Why the ECB inflation target exists
Central banks do not aim for zero inflation. In the euro area, the European Central Bank has maintained an explicit numerical target for price stability since the launch of the single currency.
The ECB gives its aim as follows:
- 2% over the medium term: After concluding its strategy review in July 2021, the ECB Governing Council considers that price stability is maintained most effectively by aiming for 2% inflation over the medium term.
- Both directions count: The ECB considers negative and positive deviations from its 2% inflation target to be equally undesirable.
The ECB gives several reasons for aiming above zero:
- Buffer against deflation: A positive target keeps monetary policy effective when inflation is too low, because interest rates can only be cut so far.
- Measurement bias: The price index may have a positive bias, so true inflation could be lower than the measured rate.
- Adjustment inside the euro area: A margin lets imbalances between countries adjust without inflation in individual countries persistently falling below zero, and it limits the risk of downward wage rigidities pushing up unemployment.
No forecasts: exploring purchasing power with interactive tools
Future inflation cannot be forecasted with certainty. Consumer price trends depend on international commodity prices, geopolitical developments, monetary policy choices, and unforeseen supply disruptions. In 2022, unexpected energy and food price surges propelled euro area inflation to 10.6% in October 2022, while previous years experienced periods near zero.
Rather than relying on speculative predictions, savers can explore the mathematical impact of different hypothetical inflation rates on their own capital:
- Purchasing power calculator: calculate how an arbitrary cash amount evolves under your chosen inflation rate and time horizon.
- ETF Calculator: explore how regular contributions in diversified index funds compound over time, comparing gross returns against fund costs (TER).
- Historical inflation timeline: explore historical consumer price developments across the United States (BLS CPI from 1913) and the euro area (Eurostat HICP from 1996) to observe how purchasing power behaved across major historical periods.
Frequently asked questions
Does my personal inflation rate match the published CPI?
Not necessarily. As the U.S. Bureau of Labor Statistics notes, the consumer price index is an average based on a representative national basket of goods and services. If you do not own a car, gasoline price swings affect you less directly than an average commuter. Similarly, if you spend a higher proportion of your income on energy or groceries than national weights assume, your individual cost of living may increase faster or slower than headline index numbers.
Does a drop in the inflation rate mean that consumer prices are going down?
No. A decline in positive inflation represents disinflation, meaning prices continue to rise, but at a slower speed. For everyday expenses to become cheaper overall, the inflation rate must become negative, which is termed deflation. Outside of specific volatile components like energy commodities, general consumer price indices rarely experience prolonged deflation.
Why does the consumer price index exclude investments and stocks?
Statistical offices design consumer price indices to measure final consumption expenditures by households. Financial instruments such as stocks, ETFs, investment properties, and bonds represent capital accumulation and savings rather than consumable goods or services. Consequently, statistical agencies such as the BLS and Eurostat exclude investment assets from the index basket.
Related pages and terms
- Purchasing power calculator: interactive tool modeling purchasing power erosion over time
- Compounding calculator: calculate compound growth on regular monthly deposits
- Getting started: educational roadmap for long-term index investing
- What does an ETF really cost?: detailed explanation of ongoing fund costs (TER) and transaction fees
- Glossary: ETF: exchange-traded fund reference definition
- Glossary: Volatility: overview of market fluctuation measurements
- Glossary: Investment horizon: guidelines on long-term holding periods
Sources
- Eurostat: Harmonised Index of Consumer Prices (HICP) methodology and definitions (ec.europa.eu/eurostat/en/web/hicp).
- Eurostat: Euro indicators news releases on annual euro area inflation (October 2022, November 2023, and annual definitions).
- U.S. Bureau of Labor Statistics (BLS): Consumer Price Index Questions and Answers (bls.gov/cpi/questions-and-answers.htm).
- U.S. Bureau of Labor Statistics (BLS): One hundred years of price change: the Consumer Price Index and the American inflation experience (Monthly Labor Review, 2014).
- European Central Bank (ECB): Price stability and the 2% inflation target (ecb.europa.eu, monetary policy strategy).