The output gap is the percentage difference between an economy's actual output and its potential output — the level sustainable without generating inflationary pressure. A positive gap signals demand running hot; a negative gap signals slack. It is a central, if unobservable, input to monetary policy and Phillips-curve inflation forecasts.
How it works
Output gap = (actual GDP − potential GDP) / potential GDP, expressed in percent. Potential output is itself a latent construct, estimated via production functions, statistical filters (e.g. Hodrick-Prescott), or multivariate models that jointly infer trend growth, NAIRU, and the gap. The estimate feeds Phillips-curve relationships linking slack to inflation and underpins rules like Taylor-type reaction functions.
Why it matters now
After the post-pandemic supply shocks scrambled potential-output estimates, central banks face unusually wide uncertainty over whether 2025-2026 economies are running with slack or excess demand — a disagreement that maps directly onto how much further policy rates can fall.
Example
In its World Economic Outlook, the IMF routinely publishes output-gap estimates: following 2008, advanced-economy gaps swung sharply negative — the euro area gap was estimated near −3% to −4% of potential GDP in 2009-2013 — yet the same data were repeatedly revised, illustrating how the gap is reliably known only years after the fact.
Frequently asked
- What is the output gap?
- The output gap is the percentage difference between an economy's actual GDP and its potential GDP — the level it can sustain without stoking inflation. A positive gap means demand is running hot; a negative gap signals slack. The IMF publishes estimates in its World Economic Outlook, where euro-area gaps ran near −3% to −4% during 2009-2013.
- How is the output gap calculated?
- The output gap equals (actual GDP − potential GDP) divided by potential GDP, expressed in percent. Potential output is unobservable, so it is estimated using production functions, statistical filters like the Hodrick-Prescott filter, or multivariate models that jointly infer trend growth
Glossary · potential growth rate
Potential growth rate is the maximum pace at which an economy can expand output without generating inflationary pressure, set by the supply-side trend of labour force growth, capital accumulation, and total factor productivity. It is unobserved and must be estimated, defining the speed limit around which the output gap is measured.
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- Why does the output gap matter for monetary policy?
- The output gap is a core input to Taylor-type reaction functions and Phillips-curve inflation forecasts, telling central banks whether to lean against excess demand or support slack. After 2020's supply shocks scrambled potential-output estimates, disagreement over whether 2025-2026 economies run hot or cold maps directly onto how far policy rates can fall.
- How does the output gap differ from potential growth?
- The output gap is a level measure — how far current output sits above or below potential at a point in time — while potential growth is the rate at which that sustainable level expands. A shock can close the gap even as potential growth slows, so the two move independently and require separate estimation.
- Why is the output gap unreliable in real time?
- The output gap depends on unobservable potential output, so real-time estimates are heavily revised as later data reshape trend assumptions. The IMF's post-2008 figures were repeatedly revised, and Orphanides' work on the 1970s showed policymakers badly misjudged slack at the time — meaning the gap is reliably known only years after the fact.