Phillips Curve
The Phillips Curve is an economic model that describes an inverse relationship between the rate of inflation and the rate of unemployment. When unemployment drops, inflation tends to rise — and vice versa. It remains one of the most debated and influential frameworks in monetary policy, shaping how the Federal Reserve thinks about interest rate decisions.
How the Phillips Curve Works
The intuition is straightforward: when the labor market is tight (low unemployment), employers compete for workers by raising wages. Higher wages push up production costs, which companies pass along as higher prices — that’s inflation. When unemployment is high, workers have less bargaining power, wage growth slows, and inflation eases.
Economist A.W. Phillips first documented this pattern in 1958 using U.K. wage data from 1861 to 1957. Paul Samuelson and Robert Solow later adapted it for the U.S. and framed it as a policy trade-off: policymakers could choose a point on the curve — lower unemployment at the cost of higher inflation, or lower inflation at the cost of higher unemployment.
The Phillips Curve Equation
Where π = actual inflation, πe = expected inflation, u = actual unemployment rate, u* = natural rate of unemployment (NAIRU), β = sensitivity of inflation to the unemployment gap, and ε = supply shock.
Short-Run vs. Long-Run Phillips Curve
| Dimension | Short-Run Phillips Curve | Long-Run Phillips Curve |
|---|---|---|
| Shape | Downward-sloping | Vertical at the natural rate of unemployment |
| Trade-off | Yes — lower unemployment means higher inflation | No — unemployment returns to NAIRU regardless |
| Expectations | Fixed (or slow to adjust) | Fully adjusted to actual inflation |
| Policy Implication | Stimulus can temporarily reduce unemployment | Sustained stimulus only raises inflation |
| Key Proponents | Keynesians (short-term) | Milton Friedman, Edmund Phelps |
Historical Track Record
| Period | What Happened | Phillips Curve Verdict |
|---|---|---|
| 1960s | Low unemployment, rising inflation | Worked well — clear trade-off |
| 1970s (Stagflation) | High unemployment AND high inflation | Broke down — challenged the model |
| 1990s–2000s | Low unemployment, low inflation | Flattened — trade-off weakened |
| 2021–2023 | Low unemployment, surging inflation | Partially confirmed — supply shocks complicated the picture |
Don’t treat the Phillips Curve as a precise forecasting tool. Think of it as a directional framework: when the labor market overheats, watch for wage-driven inflation. The curve has “flattened” over recent decades — meaning unemployment can swing more before inflation reacts — but the core relationship hasn’t disappeared. The Fed still monitors it closely when setting the federal funds rate.
Why the Phillips Curve Matters for Investors
Understanding the Phillips Curve helps you anticipate Fed behavior. When unemployment falls well below the natural rate, the Fed is more likely to hike rates — bad for bonds, potentially negative for growth stocks. When unemployment rises, rate cuts become more likely — a tailwind for fixed income and rate-sensitive sectors.
Key Takeaways
- The Phillips Curve describes an inverse relationship between inflation and unemployment.
- The short-run curve is downward-sloping; the long-run curve is vertical at the natural rate of unemployment.
- Stagflation in the 1970s challenged the model, leading to the expectations-augmented version.
- The curve has flattened in recent decades but remains a key input for monetary policy decisions.
- Investors use it to anticipate Fed rate moves based on labor-market tightness.
Frequently Asked Questions
Is the Phillips Curve still relevant today?
Yes, but with caveats. The trade-off between unemployment and inflation still exists, but it’s weaker and less predictable than in the 1960s. Globalization, anchored inflation expectations, and supply-chain dynamics have all flattened the curve. Central banks still reference it, but they rely on multiple models rather than the Phillips Curve alone.
What is NAIRU?
NAIRU stands for the Non-Accelerating Inflation Rate of Unemployment — the unemployment rate at which inflation remains stable. If unemployment falls below NAIRU, inflation tends to accelerate. The Fed estimates NAIRU at roughly 4%–4.5% for the U.S., but it’s not directly observable and shifts over time.
Why did the Phillips Curve break down in the 1970s?
The 1970s brought oil supply shocks that pushed inflation higher while simultaneously causing recessions (higher unemployment). The original Phillips Curve couldn’t explain simultaneous high inflation and high unemployment — “stagflation.” Milton Friedman and Edmund Phelps had predicted this breakdown, arguing that inflation expectations would shift the curve.
How does the Phillips Curve affect interest rates?
When unemployment drops below the natural rate, the Phillips Curve suggests inflation will rise. The Federal Reserve responds by raising the federal funds rate to cool the economy. Conversely, rising unemployment signals deflationary pressure, prompting rate cuts.
What is the difference between the Phillips Curve and the Taylor Rule?
The Phillips Curve describes the relationship between unemployment and inflation. The Taylor Rule prescribes what interest rate the central bank should set based on the inflation gap and the output (or unemployment) gap. The Taylor Rule essentially uses the Phillips Curve relationship as an input to recommend a specific policy rate.