Inflation: CPI, Core vs Headline, Real Returns

What you will learn

• What inflation is and how a consumer price index measures it.
• The difference between headline and core inflation.
• How to convert a nominal return into a real return.
• Why inflation data moves rates, currencies and other markets.

Explanation

Inflation is the general rise in prices over time. When inflation is 3%, a basket of goods that cost €100 a year ago costs about €103 today. Your money buys less.

Inflation is measured with a price index. In the United States the best-known is the CPI (Consumer Price Index), published monthly by the Bureau of Labor Statistics. In the euro area, the main measure is the HICP (Harmonised Index of Consumer Prices), published by Eurostat; this is the index the ECB uses for its target. Germany also publishes national figures through Destatis, the Federal Statistical Office.

Inflation is usually reported as a year-over-year change (compared with the same month last year) and sometimes as a month-over-month change (compared with the previous month).

• Headline inflation includes all items in the basket, including energy and food.
• Core inflation excludes items whose prices jump around a lot, usually energy and food (the exact definition differs between measures). Core helps to see the underlying trend.

A nominal return is the return in money terms, for example "my account grew by 5%". A real return is the return after inflation: how much more you can actually buy.

Quick approximation: real return ≈ nominal return − inflation. The exact formula is: real return = (1 + nominal) ÷ (1 + inflation) − 1.

Why markets care: higher-than-expected inflation can make central banks keep rates higher for longer. That can lift bond yields, support the currency and pressure assets that are sensitive to rates, such as growth stocks. These are tendencies; the reaction depends on what was already expected.

Worked example

Hypothetical example: you invest €10,000 for one year. The nominal return is 5% and inflation over the same year is 3%. Excluded: fees and taxes.

1. Value after one year: €10,000 × 1.05 = €10,500.
2. Approximate real return: 5% − 3% = 2%.
3. Exact real return: 1.05 ÷ 1.03 − 1 = 0.01942 ≈ 1.94%.
4. Purchasing power in today's euros: €10,500 ÷ 1.03 = €10,194.17.

You have €500 more on paper, but only about €194 more in real buying power. If inflation had been 6%, the real return would be negative even though the account balance went up.

Common mistake

Practice activity

On paper: you hold €20,000 in a savings account paying 4% for one year. Inflation is 6%. Calculate the nominal value after one year, the exact real return, and the purchasing power in today's euros. Ignore taxes.

Key takeaways

• Inflation reduces what your money can buy; CPI and HICP measure it.
• Headline includes energy and food; core excludes volatile items to show the trend.
• Real return = (1 + nominal) ÷ (1 + inflation) − 1.
• Inflation surprises can move rate expectations and therefore many markets.

Next step

In the next lesson you will learn why the US dollar plays a special role and how its strength tends to affect gold, Bitcoin and other markets.