What is the natural rate of unemployment (NAIRU)?

The Non-Accelerating Inflation Rate of Unemployment (NAIRU) is the theoretical unemployment rate at which inflation neither rises nor falls. When actual unemployment drops below NAIRU, the tight labor market generates upward pressure on wages and prices, accelerating inflation. When unemployment is above NAIRU, the slack in the labor market suppresses wage and price growth, decelerating inflation.

NAIRU cannot be directly observed; it must be estimated, and estimates vary significantly across models and time periods. The Congressional Budget Office maintains a long-run NAIRU estimate that has hovered around 4.0-4.5% in recent years. The Fed's longer-run projection for unemployment in the Summary of Economic Projections (SEP) serves as its implicit NAIRU estimate and has been revised from 5.6% in 2012 to approximately 4.0-4.2% more recently.

The concept has been challenged by real-world experience. During the late 2010s, unemployment fell to 3.5% with minimal inflation, suggesting either that NAIRU was lower than previously estimated or that the Phillips curve had flattened. The 2021-2023 inflation episode complicated the picture further, as inflation surged when unemployment was low but also when massive supply shocks and fiscal stimulus were operating simultaneously, making it difficult to isolate the labor market's contribution.

For monetary policy, NAIRU serves as a guidepost rather than a precise target. When the Fed sees unemployment falling well below its NAIRU estimate and inflation starting to accelerate, it interprets this as confirmation that the labor market is overheating and tightening is warranted. When unemployment rises above NAIRU with inflation cooling, the case for easier policy strengthens. The imprecision of NAIRU estimates is why the Fed describes its policy as "data dependent" rather than mechanically tied to any single unemployment threshold.