What Is CPI (Consumer Price Index)?
Definition
CPI (Consumer Price Index): An index of the price level of a basket of goods and services that households buy. The national statistics office publishes it every month; official inflation is its yearly change.
The consumer price index (CPI, TÜFE in Turkish) measures the price level of a basket of goods and services that households buy. A national statistics office publishes it every month. Official inflation is the yearly change of the index. Rent increase caps in some countries and real return calculations start from it.
Where it appears in the formulas
yearly change = (this month's index / same month last year's index − 1) × 100, and 12-month average change = (average of the last 12 months / average of the 12 months before − 1) × 100. The rent increase calculator uses the 12-month average change of the month before the renewal. The inflation calculator uses a fixed rate you choose, not CPI data.
In Türkiye
TÜİK publishes the index every month as TÜFE. The legal cap on rent increases for homes and roofed workplaces is the CPI’s 12-month average change (Code of Obligations no. 6098, art. 344). TÜİK moved the index base from 2003=100 to 2025=100 in January 2026.