Consumer Price Index (CPI)

A representative price index that measures changes in the prices of goods and services purchased by households, serving as a key benchmark for monetary policy and for wage and pension adjustments.

Consumer Price Index (CPI)

Overview

The Consumer Price Index (CPI) is a representative price index that measures changes in the prices of goods and services that households purchase in their daily lives. It is published monthly by Statistics Korea (통계청) and is widely used as a benchmark for judging inflation, deciding monetary policy, and adjusting wages, pensions, and the minimum wage. Each country's statistical agency produces it independently, but the OECD and ILO issue common recommendations for international comparison.

Key Details

Definition and Calculation Method

The CPI is a value that indexes the change in current consumer purchase prices relative to a base period (e.g., 2020 = 100). Rather than simply averaging the prices of each item, it is calculated using the Laspeyres formula, reflecting the share of household consumption expenditure (weights). In other words, price changes in items with a large expenditure share are reflected more heavily in the index. Items and weights are revised based on the Household Income and Expenditure Survey conducted at regular intervals (every 5 years in Korea), which is called a "base year revision."

Sub-indices and Classification

Headline index: the basic index covering all representative items
Living necessities price index (생활물가지수): composed of items with high purchase frequency and a large expenditure share (about 140 items), closely approximating perceived inflation
Fresh food index (신선식품지수): items with high volatility such as fresh fish and seafood, vegetables, and fruit
Core inflation (index excluding agricultural products and petroleum products): removes temporary external shocks to identify the underlying price trend
Index including owner-occupied housing costs: reflects the opportunity cost of home ownership and is used for international comparisons

Economic Uses

1. Monetary policy: Central banks judge whether the inflation target (2% in Korea) is being met and adjust the policy rate.

2. Income and contract adjustment: Serves as the benchmark for preserving the real value of wage negotiations, pension benefits, the minimum wage, and various fees.

3. Calculating real variables: Used as a deflator when deriving real interest rates, real income, and real wages.

4. Financial markets: Used as the underlying indicator for derivatives such as inflation-linked bonds (TIPS) and inflation swaps.

5. Policy evaluation: Provides the basis for analyzing changes in the real burden of tax and welfare policies.

Limitations and Criticism

Substitution bias: Consumers substitute items whose prices have risen with relatively cheaper items, but the fixed-basket method cannot reflect this and may overestimate the inflation rate.
Quality change: Performance improvements in technology products such as smartphones can be mistaken for price declines, so quality adjustment is necessary.
Housing cost controversy: There are persistent criticisms that jeonse and owner-occupied housing costs diverge from actual perceived costs.
The trap of averages: Because it is based on the average of all households, it differs from the perceived inflation of specific groups such as single-person households and elderly households.

Recent Trends

The global CPI trend in 2024–2025 has entered a phase of clear slowdown. Consumer price inflation in the United States and the Eurozone, which had soared to 8–10% in 2022, stabilized in the 2–3% range in 2024, with falling energy prices and base effects acting as the main factors.

However, the stickiness of service prices is a new variable. Inflation in the service sector—housing costs, dining out, insurance premiums, and the like—remains higher than goods prices, constraining the pace of policy easing. The U.S. Federal Reserve entered a rate-cut cycle in the second half of 2024, but market interest rates and stock prices continue to fluctuate significantly depending on the monthly CPI results.

In Korea, with inflation hovering between the mid-1% range and the early 2% range, the Bank of Korea is seeking a balance between price stability and sluggish domestic demand. In addition, the impact of productivity changes from the spread of AI and automation on the medium- to long-term inflation path, increased volatility in agricultural prices due to climate change, and discussions on shortening the base year revision cycle are being actively addressed in academia and by policy authorities. Recently, "nowcasting" techniques that measure near-real-time prices using big data and scanner data are also spreading.