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What is NAIRU?

NAIRU stands for the non-accelerating inflation rate of unemployment. It is the unemployment rate at which inflation neither accelerates nor decelerates—it remains stable. In other words, NAIRU is another name for the natural rate of unemployment, just with an explicit emphasis on inflation stability. When actual unemployment equals NAIRU, wage growth moves in line with productivity growth, and price pressures remain in equilibrium.

NAIRU is critical for monetary policy because the Federal Reserve and other central banks use it as a target. When unemployment is above NAIRU, there is slack in labor markets, and inflation tends to fall. When unemployment is below NAIRU, labor markets are tight, and inflation tends to rise. By keeping unemployment near NAIRU, the Fed aims to maintain stable inflation while avoiding unnecessary unemployment.

The concept emerged in the 1960s when economists noticed that the original Phillips curve relationship between unemployment and inflation was not as simple as first believed. Simply having low unemployment did not guarantee stable inflation; there was a threshold below which inflation would accelerate. That threshold is NAIRU.

Quick definition: NAIRU is the unemployment rate at which inflation is stable and neither accelerating nor decelerating; approximately 4.5% in the modern U.S.

Key takeaways​

  • NAIRU is the unemployment rate consistent with stable inflation; it is identical to the natural rate of unemployment, just with emphasis on the inflation link.
  • Below NAIRU, inflation accelerates; above NAIRU, inflation decelerates. At NAIRU, inflation is steady.
  • NAIRU cannot be observed directly and must be estimated using Phillips curves, surveys, or structural models.
  • NAIRU has shifted over time due to demographic changes, education levels, and labor market efficiency improvements.
  • The Federal Reserve targets monetary policy to keep unemployment near NAIRU, raising rates when unemployment is below NAIRU (to prevent inflation) and cutting rates when unemployment is above NAIRU (to boost growth).
  • The Phillips curve relationship between unemployment and inflation is flatter than it once was, making NAIRU estimates more uncertain.

NAIRU versus natural rate: the same concept with different emphasis​

The natural rate of unemployment and NAIRU are mathematically identical. Both are the unemployment rate at which labor supply equals labor demand, and both are the threshold below which inflation accelerates. The difference is purely terminological.

"Natural rate" emphasizes that this is the rate determined by structural features of the economy (demographics, education, job matching efficiency). It is "natural" in the sense that it is not artificially kept high or low by policy.

"NAIRU" emphasizes that this is the rate that keeps inflation non-accelerating. It is the inflation-targeting rate. While economists often use the terms interchangeably, NAIRU is more common in discussions of monetary policy because it explicitly connects unemployment to inflation, which is the central bank's mandate.

The relationship is straightforward:

  • Unemployment = NAIRU: Labor markets are in equilibrium. Wage growth equals productivity growth. Inflation is stable.
  • Unemployment < NAIRU: Labor markets are tight. Wage growth exceeds productivity growth. Firms raise prices to cover higher wages. Inflation accelerates.
  • Unemployment > NAIRU: Labor markets have slack. Wage growth lags productivity growth. Firms hold prices steady or cut them. Inflation decelerates.

How NAIRU relates to the Phillips curve​

The Phillips curve is the empirical relationship between unemployment and inflation. It is typically drawn as a downward-sloping line: lower unemployment corresponds to higher inflation. NAIRU is the point where the Phillips curve crosses the horizontal line representing the desired inflation rate (typically 2% for the Federal Reserve).

Imagine a Phillips curve based on recent U.S. data. At 6% unemployment, inflation might be 1%. At 4% unemployment, inflation might be 2% (NAIRU). At 2% unemployment, inflation might be 4%. The Phillips curve slopes downward from left to right.

NAIRU is the unemployment rate at which the Phillips curve crosses 2% inflation (the Fed's target). Below that point, inflation exceeds the target. Above that point, inflation is below the target. The Fed uses NAIRU to decide whether it should tighten (raise rates) or loosen (cut rates).

However, the Phillips curve has shifted over time. In the 1960s, the relationship was steep, suggesting NAIRU was around 4% or 5%. In the 1990s, the relationship flattened, and some economists argued NAIRU was as low as 3% to 3.5%. In the 2010s, the relationship flattened further, making NAIRU estimates even more uncertain.

A flatter Phillips curve means inflation responds less to unemployment changes. This makes NAIRU harder to estimate and raises the question of whether the concept is as useful as it once was. If inflation barely responds to unemployment changes, then NAIRU's importance diminishes.

Estimating NAIRU in practice​

The Federal Reserve and academic economists use several methods to estimate NAIRU. (The Federal Reserve publishes NAIRU estimates in its Summary of Economic Projections.)

Method 1: Phillips curve regression. Run a statistical regression linking unemployment to inflation. The unemployment rate at which inflation equals the target (usually 2%) is NAIRU. Recent estimates yield roughly 4% to 4.5%. The challenge is that the Phillips curve shifts over time, so estimates based on recent data differ from those based on longer historical periods.

Method 2: Survey expectations. Ask firms and workers about their inflation expectations. If most expect inflation to remain near 2%, you can infer the unemployment rate at which these expectations are consistent. This is NAIRU. The advantage is that expectations-based estimates are less dependent on past inflation data. The disadvantage is that surveys can be wrong or biased.

Method 3: Unobserved components model. Treat NAIRU as a hidden, slowly-moving variable that is consistent with observed inflation and unemployment. Use statistical algorithms (like the Kalman filter) to estimate what NAIRU must be given the data. This is mathematically sophisticated but requires strong assumptions about how NAIRU moves over time.

Method 4: Structural models. Build a detailed economic model including labor supply, labor demand, wage-setting, and pricing. Solve the model for equilibrium unemployment. This can yield precise estimates but requires assumptions about underlying economic structure that may not hold.

The Federal Reserve publishes estimates using multiple methods. Currently, Fed estimates of NAIRU range from 4.0% to 5.0%, with a central estimate around 4.5%. This range reflects genuine uncertainty about the true NAIRU. Different methods yield different answers, and the truth likely lies somewhere in the range.

NAIRU's relationship to the output gap​

The output gap is the difference between actual economic output and potential output (the output the economy could produce at full capacity and at NAIRU). When unemployment equals NAIRU, the output gap is zero by definition. When unemployment is below NAIRU, output exceeds potential and the output gap is positive. When unemployment is above NAIRU, output falls short of potential and the output gap is negative.

The output gap is useful because it measures spare capacity in the economy. A large negative output gap (unemployment well above NAIRU) indicates significant slack and room to stimulate without inflation risk. A large positive output gap (unemployment well below NAIRU) indicates the economy is overheating and needs restraint.

The Fed estimates the output gap alongside NAIRU estimates. (See the Federal Reserve's economic research on output gaps.) If unemployment is currently 4% and estimated NAIRU is 4.5%, the implied gap suggests unemployment is 0.5 percentage points below NAIRU, indicating slight overheating (demand exceeds capacity). If inflation is stable at 2%, the Fed might hold rates steady or wait for unemployment to rise to NAIRU through normal economic cycles.

Why NAIRU shifted lower in the 1990s​

In the 1990s, many economists and Fed officials revised down their estimates of NAIRU from 5% to 6% toward 4% to 4.5%. Why?

Several factors contributed:

Productivity acceleration. The digital revolution and the internet began spreading through the economy. Workers with computers and software could produce more output. Higher productivity meant wage growth could accelerate without requiring higher inflation. This allowed the economy to run with lower unemployment (below the old 5% estimate) without triggering inflation. Some estimates suggested productivity growth could support NAIRU as low as 3.5%.

Globalization. Competition from imports increased in the 1990s, suppressing wage growth. A U.S. worker might have gotten a 5% raise in the 1970s, but in the 1990s only a 3% raise because wages were being suppressed by competition from cheaper foreign workers. Lower wage growth allowed lower unemployment without triggering inflation.

Unemployment level itself. Unemployment fell below 4% in the late 1990s without triggering significant inflation, which surprised many economists. This empirical observation revised down NAIRU estimates. If 3% unemployment had not caused inflation, maybe NAIRU was lower than 4.5%.

The result: the Fed kept rates low through the late 1990s, stimulating the economy and contributing to the tech bubble. When the bubble burst in 2000, economists debated whether they had misjudged NAIRU.

How central banks use NAIRU to set policy​

The Federal Reserve follows a framework for setting monetary policy based on NAIRU and output gaps:

  1. Estimate NAIRU. Using Phillips curves, surveys, and models, estimate current NAIRU (roughly 4.5%).
  2. Compare to actual unemployment. Is unemployment above or below NAIRU? If unemployment is 3%, it is 1.5 percentage points below NAIRU. If unemployment is 5.5%, it is 1 percentage point above NAIRU.
  3. Assess inflation. If unemployment is below NAIRU, inflation should be rising or high. If unemployment is above NAIRU, inflation should be falling or low.
  4. Decide policy. If unemployment is below NAIRU and inflation is rising, tighten (raise rates). If unemployment is above NAIRU and inflation is low, loosen (cut rates). If unemployment equals NAIRU and inflation is on target, hold steady.

This framework is not rigid—the Fed also considers forward guidance, expectations, and other factors. But NAIRU is central to the Fed's thinking.

The 2021-2023 period illustrates how this works. In mid-2021, unemployment was around 5%, and NAIRU estimates were around 4%. This suggested 1 percentage point of slack, so the Fed kept rates near zero, expecting more stimulus was appropriate. But inflation began rising, suggesting the economy was overheating. The Fed eventually concluded it had misjudged NAIRU (or that NAIRU itself had fallen due to labor shortages) and began raising rates aggressively in 2022.

Historical NAIRU estimates and shifts​

Estimated NAIRU has changed significantly over the past 50 years:

  • 1960s: NAIRU estimated at 4% to 4.5%. The Phillips curve was stable, and low unemployment consistently produced higher inflation.
  • 1970s: NAIRU estimates rose to 5% to 6%. Stagflation (simultaneous high inflation and unemployment) suggested the Phillips curve had shifted, pushing NAIRU higher.
  • 1980s: NAIRU estimates peaked at 5.5% to 6%, reflecting the Volcker Fed's belief that high unemployment was necessary to break inflation expectations.
  • 1990s: NAIRU estimates fell to 4% to 4.5%, and some economists argued for 3.5% or even 3%, based on the tech boom, productivity acceleration, and the experience of low unemployment without inflation.
  • 2000s: NAIRU estimates stabilized around 4.5% to 5%. The tech bubble burst, but productivity growth remained solid.
  • 2010s: NAIRU estimates fell slightly to 4% to 4.5% as the Fed debated whether slack remained even as unemployment fell to 3.7%.
  • 2020s: NAIRU estimates remain uncertain, around 4% to 5%, but the experience of tight labor markets and rising wages suggests the economy may have overheated below 4% unemployment.

These shifts reflect both genuine changes in the economy and uncertainty about the true NAIRU. The widening of the Fed's range (4.0% to 5.0%) reflects this uncertainty.

The Phillips curve flattening and NAIRU uncertainty​

A major development in recent decades is the flattening of the Phillips curve. In the 1960s and 1970s, a 1-percentage-point drop in unemployment corresponded to a 0.5 to 1-percentage-point rise in inflation. The Phillips curve was steep, and inflation responded sharply to unemployment changes.

By the 2010s, a 1-percentage-point drop in unemployment corresponded to only a 0.1 to 0.2-percentage-point rise in inflation. The Phillips curve was flat, and inflation barely responded to unemployment changes.

This flattening has several explanations:

Inflation expectations anchoring. If workers and firms expect inflation to remain near 2%, they do not adjust wages and prices much in response to tight labor markets. The inflation expectation becomes an anchor that constrains actual inflation. With anchored expectations, the Phillips curve flattens.

Globalization. Continued import competition suppresses wages even when unemployment is low. Workers cannot demand high wage increases without risking job loss to outsourcing.

Labor market changes. Gig work, contractor arrangements, and declining union membership have weakened workers' bargaining power. Tight labor markets may translate less directly into wage pressure.

Measurement issues. Some economists argue the Phillips curve has not actually flattened; it is just harder to measure with available data.

A flatter Phillips curve makes NAIRU less important for policy. If inflation barely responds to unemployment, then pushing unemployment below NAIRU does not create much inflation problem. Some economists now argue the Fed should focus on actual inflation data rather than unemployment gaps and NAIRU estimates.

Common mistakes​

Mistake 1: Treating NAIRU as a fixed number. NAIRU changes over time as demographics, education, and labor market efficiency evolve. A NAIRU estimate of 4.5% in 2020 may be 4.0% or 5.0% in 2030. Policymakers update estimates regularly.

Mistake 2: Assuming the Phillips curve relationship is stable. The Phillips curve has shifted multiple times in history. In some decades it is steep, in others flat. A NAIRU estimate based on 2010s data (flat Phillips curve) might be wrong if the Phillips curve steepens again.

Mistake 3: Confusing NAIRU with zero inflation. NAIRU is the rate at which inflation is stable, not zero. If stable inflation is 2%, then at NAIRU, inflation is 2%. NAIRU does not mean zero inflation; it means constant inflation.

Mistake 4: Thinking the Fed can target unemployment below NAIRU permanently. The Fed can push unemployment below NAIRU temporarily through stimulus, but sustained attempts will only accelerate inflation without permanently lowering unemployment. Eventually, inflation rises high enough that the Fed must tighten, pushing unemployment back up.

Mistake 5: Ignoring that NAIRU estimates have large uncertainty bands. The Fed publishes estimates ranging from 4.0% to 5.0%, yet policymakers sometimes discuss the midpoint (4.5%) as if it is known with certainty. The actual NAIRU could be outside this range. Humility about NAIRU is appropriate.

FAQ​

Is NAIRU the same as full employment?​

Approximately yes. Full employment is often defined as the unemployment rate at which the economy is operating at capacity and inflation is stable. That is NAIRU. However, "full employment" can sometimes mean zero unemployment, which is impossible and undesirable. NAIRU is a more precise term.

How often does the Fed update NAIRU estimates?​

The Federal Reserve publishes updated NAIRU estimates quarterly in its Summary of Economic Projections (SEP). The estimates incorporate new data on inflation, unemployment, and expectations. However, NAIRU estimates change slowly—the Fed's estimates typically shift by 0.1 to 0.2 percentage points per year, not dramatically.

What happens if the true NAIRU is lower than estimated?​

If the Fed overestimates NAIRU and the true NAIRU is 4% while the estimate is 4.5%, the Fed will be too restrictive. Unemployment will stay higher than necessary, reducing growth and employment. The Fed will eventually recognize the error, lower NAIRU estimates, and begin cutting rates.

What happens if the true NAIRU is higher than estimated?​

If the Fed underestimates NAIRU and the true NAIRU is 5% while the estimate is 4.5%, the Fed will be too loose. Unemployment will fall below the true NAIRU, inflation will accelerate, and the Fed will have to tighten aggressively, pushing unemployment up and possibly triggering recession. This is worse than overestimating NAIRU, so some economists advocate for caution.

How does NAIRU differ across countries?​

Different countries have different NAIRU estimates based on their demographic structure, education levels, and labor market institutions. The U.S. NAIRU is estimated around 4% to 5%. The eurozone NAIRU is typically estimated around 5% to 5.5% (higher, reflecting more labor market rigidity and structural unemployment). Japan's NAIRU is estimated lower, around 3%, reflecting demographic decline and weak wage growth.

Can NAIRU be estimated without assuming a Phillips curve?​

Yes. Some economists estimate NAIRU using surveys of inflation expectations and labor demand measures (job openings, help-wanted indices). Others use structural models that do not rely on Phillips curve estimation. However, most modern estimates do use Phillips curves as one input among several.

Summary​

NAIRU (the non-accelerating inflation rate of unemployment) is the unemployment rate at which inflation is stable. It is identical to the natural rate of unemployment, just with emphasis on the inflation connection. At NAIRU, wage growth moves in line with productivity growth, and price pressures remain in equilibrium. Below NAIRU, inflation accelerates; above NAIRU, inflation decelerates. The Federal Reserve uses NAIRU estimates to guide monetary policy, raising rates when unemployment falls below NAIRU and cutting rates when it rises above. NAIRU cannot be observed directly and must be estimated, currently in the range of 4% to 5% for the U.S. The Phillips curve has flattened in recent decades, making NAIRU less important for inflation outcomes than it once was and introducing uncertainty into NAIRU estimates.

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