Recessions are stretches of meaningful contraction in economic activity, and economists and policymakers have an awkward relationship with them: by the time the official call is made, the recession is well underway. Among the various indicators proposed to identify a downturn earlier, one stands out for the rare combination of arithmetic simplicity and empirical reliability. The Sahm Rule, developed by former Federal Reserve economist Claudia Sahm, produces a clear binary signal from a single readily available data series: the unemployment rate. In mid-2024, the rule triggered for the first time since the COVID-19 contraction — under conditions Sahm herself has publicly described as not quite fitting the historical pattern.
The mechanic
The Sahm Rule is one sentence long. A recession has likely begun, the rule says, when the three-month moving average of the national unemployment rate rises by at least 0.50 percentage points above the lowest three-month moving average of the previous twelve months.
That is the entire definition. The signal is binary: above 0.50, the rule fires; below, it does not. There is no smoothing, no discretion, no judgement call. Because the unemployment-rate series is published monthly and revised rarely, the rule produces a near-real-time call without relying on the volatile financial-market indicators that dominate recession-prediction commentary.
The track record
Since its introduction, the Sahm Rule has correctly flagged every official US recession as classified by the National Bureau of Economic Research, including the 1973–1975 contraction, the early-1980s double-dip, the early-1990s contraction, the dot-com bust of 2001, and the 2007–2009 Great Recession. False positives have been rare.
The structural reason the rule works is that recessions almost always involve a rapid deterioration in the labour market. Unemployment as a series is often treated as a lagging indicator — by the time joblessness rises, the contraction is already underway — but the rate of change in the labour market is informative about the trajectory, not just the level. The Sahm Rule extracts the signal from the second derivative of the unemployment series while keeping the data inputs to one.
Sahm designed the rule with a policy purpose: to provide an objective, rules-based real-time trigger that could activate automatic fiscal stabilisers — direct transfers, extended unemployment benefits — at the point a downturn became recognisable rather than after legislative debate concluded. That purpose has been less successful than the analytical properties of the rule itself; no major economy currently ties statutory stabiliser triggers to the rule.
The limits
The Sahm Rule is not a leading indicator. By the time the threshold is crossed, the labour market has already softened materially. It is most useful in moments when other indicators are sending mixed signals, because the unemployment series is unusually clean. It is also of limited use in identifying very short, sharp downturns — the two-month COVID-19 contraction of 2020 fits this profile poorly — and structural changes in the labour market (the growth of gig-economy work, the re-distribution of remote work, the participation-rate effects of demographic transitions) may require adjustments to the threshold.
The mid-2024 trigger
The rule crossed its threshold in July 2024. The unemployment rate that month came in at 4.3%, against consensus expectations of 4.1%. The three-month moving average reached 4.13%, up from a low of 3.50% in July 2023. The 0.63 percentage-point gap between the two cleanly exceeded the 0.50-point trigger.
Two features of the trigger were unusual. First, the upward move in the unemployment rate was driven less by job losses than by an increase in the labour force — more people looking for work, against continued positive job creation. Second, the headline economic data through the trigger period remained broadly supportive: GDP growth held up, consumer spending was steady, and the high-frequency activity indicators that usually deteriorate alongside the labour market did not.
Sahm herself addressed the trigger publicly, in unusually cautious terms: the current situation differs from the textbook pre-recession pattern in ways the rule was not designed to handle, and the trigger this time should be read as a warning rather than a confirmed recession call.
The policy implication
For monetary policy, the trigger sits inside an already-eased path. The Federal Reserve’s rate-cutting cycle was underway before the signal fired; the question for the FOMC is whether the labour-market trajectory accelerates the pace of cuts. For fiscal policy, the trigger has revived the academic debate Sahm originally motivated: whether automatic stabilisers tied to a Sahm-style rule should be embedded in statute, so that the next downturn produces transfer-payment support without requiring a legislative process that historically runs months behind the data.
For market participants, the practical implication is more limited. The rule is a labour-market indicator, not a positioning signal; the historical pattern is that risk markets typically priced the deterioration before the rule fired. The value of the signal lies less in what it implies for the next week of price action than in what it implies for the next two quarters of policy.
Translated and re-edited for English-language publication from the German original published by the Vereinigung Technischer Analysten Deutschlands e.V. (VTAD), reproduced with the author’s permission.