Peak vs Trough
Peak and Trough are two The Business Cycle concepts in AP Economics that students often mix up. The peak is the highest point of economic activity in a business cycle. The trough is the lowest point of economic activity in a business cycle. Here is how they compare side by side.
The peak represents the end of an expansion and the beginning of a contraction. At the peak, an economy's real GDP stops increasing and starts to decline. Unemployment is low, and inflation may be high.
The trough represents the end of a contraction and the beginning of an expansion. At the trough, an economy's real GDP stops decreasing and starts to increase. Unemployment is high, and inflation is typically low.
Peak vs Trough: Two Turning Points, Opposite Conditions
| Peak | Trough | |
|---|---|---|
| What the point marks | The last month of an expansion and the first of a contraction | The last month of a contraction and the first of a recovery |
| Real GDP | A local maximum for that cycle, not an all-time high | A local minimum for that cycle, often still above an earlier peak |
| Unemployment rate | At its cyclical low, and often still drifting down for a quarter after the peak | At or near its cyclical high, and often still rising for a quarter after the trough |
| Output gap | Most positive of the cycle, so the inflationary gap is widest here | Most negative of the cycle, so the recessionary gap is widest here |
| Inflation pressure | Strongest, with wages and input costs bidding up | Weakest, with disinflation or outright deflation on the table |
| What comes next | A contraction, so policy aimed at the boom lands during the downturn | A recovery, which begins while the labor market still looks awful |
A later trough can sit above an earlier peak, because the trend keeps rising
Cycles ride on a rising long-run trend, so peak and trough are local labels rather than absolute ones. Take a hypothetical economy with real GDP in billions of dollars. The first cycle peaks at 540 and bottoms at 512. Growth resumes, and the next cycle peaks at 596 before bottoming at 578. That second trough of 578 is the worst point of its own cycle and still sits well above 540, the best point of the previous one. Nothing about that is contradictory. A peak is the highest point within one cycle and a trough is the lowest point within one cycle, and both are defined by the change of direction on either side, not by any comparison across cycles. This is why questions asking which point had the lowest real GDP always tie the answer to a specific cycle, and why the claim that a trough must be the worst outcome anywhere in the series is false whenever the trend is upward. The working rule for a stimulus is short: find the cycle first, then read the extremes inside it.
Growth passes through zero at both, so only the signs on either side separate them
Real GDP is momentarily flat at a peak and flat again at a trough, so a growth rate near zero is compatible with either one and a single reading settles nothing. What separates them is the sign on each side. A peak has positive growth before it and negative growth after it, so the path bends downward. A trough has negative growth before it and positive growth after it, so the path bends upward. Free-response prompts exploit this by handing you a table of quarterly growth rates and asking which quarter is the turning point, and the reliable method is reading the signs in order rather than hunting for the largest or smallest number in the column. The same rule picks the policy stance. At a peak the output gap is at its most positive, so the answer has to address an inflationary gap and contractionary policy is the textbook prescription. At a trough the gap is at its most negative, so expansionary policy is the prescription. Neither prescription is available in real time, because a turning point can only be dated once the quarters on both sides of it exist.
The unemployment rate is often still rising after the trough has passed
Employment lags output. Firms cut hours before they cut jobs and rebuild hours before they rehire, so the unemployment rate usually reaches its highest reading a quarter or two after real GDP has already turned up at the trough. A stimulus showing unemployment rising is therefore fully consistent with an early expansion, which is the most common misreading on business-cycle questions. The same delay runs in reverse at a peak, where unemployment can still be drifting down after output has turned over, so a falling unemployment rate is not proof that the expansion is still running. Two habits keep this straight. Treat real GDP as the series that dates the turning points, and treat unemployment as confirmation that arrives late. When a question hands you both and they disagree, follow output. The lag also explains a policy pattern worth naming in an answer. Turning points get identified only after the fact, once several months of data exist and revisions have settled, so a fiscal package designed during a contraction can easily reach the economy after the trough it was meant to prevent, adding demand to an economy that has already turned.
Frequently asked questions
Is the peak of the business cycle the healthiest point for an economy?
Peaks combine the highest real GDP of a cycle with the strongest inflation pressure, so a peak is not automatically the healthiest position. At a peak, output typically sits above potential, unemployment sits below the natural rate, and wages and input costs are bidding up, which describes an unsustainable state rather than an ideal one. Long-run health is better measured by potential output, which depends on resources, capital, and technology rather than on where the cycle happens to sit. A peak also guarantees that a contraction comes next.
Can real GDP at a trough be higher than at an earlier peak?
Real GDP at a trough can easily exceed real GDP at an earlier peak, because cycles ride on a rising long-run trend. Peak and trough label the highest and lowest points within a single cycle, never across the whole series. In the sequence 540, 512, 596, 578, the second trough of 578 outranks the first peak of 540 while remaining the worst point of its own cycle. Compare a peak with a trough only inside the same cycle.
What happens to inflation at a trough?
Inflation is usually at its weakest around a trough. Aggregate demand is at its lowest relative to potential output, the recessionary gap is widest, and firms have little room to raise prices while capacity sits idle. In most cases that produces disinflation, meaning the inflation rate falls while prices still rise slowly. A deep enough contraction can push the rate below zero into deflation. The exception is a trough caused by a supply shock, where prices can climb while output bottoms out.
Live Business Cycle graph. Drag the curves, or open the full version.
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