What is sticky vs flexible CPI?

The Federal Reserve Bank of Atlanta divides the CPI basket into two categories based on how frequently prices change. "Sticky" prices are those that change infrequently, such as rent, medical care, education, insurance, and restaurant meals. "Flexible" prices are those that adjust rapidly, including gasoline, food at home, used vehicles, airfares, and apparel. Each component is classified based on the median frequency of its price adjustments.

The sticky CPI is valuable because it embeds forward-looking information about inflation expectations and labor costs. When a landlord sets a rent or a hospital sets its rates, those prices tend to persist for months or years. The decisions reflect expected future costs, particularly wages, which are the largest input for service-sector businesses. As a result, sticky CPI tends to be a better predictor of where inflation is headed than either headline or core CPI.

Flexible CPI, by contrast, captures supply-driven shocks that can dominate headlines but often reverse. The oil price spike in 2022, the used car price surge in 2021, and the egg price explosion in 2023 were all captured in flexible CPI but had limited predictive power for underlying inflation. Flexible CPI tends to be mean-reverting, making it useful for understanding what is temporarily pushing headline inflation but less useful for gauging persistent trends.

The divergence between sticky and flexible CPI often reveals the stage of the inflation cycle. In early 2021, flexible CPI surged while sticky remained moderate, correctly signaling that much of the initial inflation was supply-driven. By late 2022, sticky CPI was accelerating even as flexible CPI cooled, warning that inflation had broadened into the service sector and would be harder to dislodge. Monitoring both measures together gives a more complete picture than any single inflation number can provide.