The Sahm Rule is a recession indicator that triggers when the three-month moving average of the national unemployment rate rises by 0.50 percentage points or more above its lowest point in the preceding twelve months. Named for the economist Claudia Sahm, who developed it while working at the Federal Reserve Board, the rule has identified every American recession since 1970 with zero false positives — a perfect record that no other single economic indicator can claim. When the rule triggers, it does not predict that a recession is coming. It announces that a recession has already begun — that the labor market has shifted from cooling to contracting, and that the self-reinforcing dynamics of rising unemployment are in motion.
The Mechanics
The calculation is precise. Take the monthly national unemployment rate as reported by the Bureau of Labor Statistics in the Employment Situation report (published on the first Friday of each month). Calculate the three-month moving average of that rate. Compare it to the lowest three-month moving average recorded in the prior twelve months. If the current average exceeds the prior low by 0.50 percentage points or more, the rule has triggered.
The three-month average smooths out monthly noise — a single-month spike in unemployment due to weather, strikes, or seasonal adjustment anomalies does not trigger the rule. The 0.50-percentage-point threshold is calibrated to distinguish between the normal fluctuation of a healthy labor market (unemployment rising from 3.5 to 3.8 percent as the Fed tightens) and the structural deterioration of a recessionary labor market (unemployment rising from 3.5 to 4.2 percent as layoffs accelerate and hiring freezes).
The mechanism that makes the Sahm Rule work is the nonlinearity of labor market downturns. When unemployment rises by 0.2 or 0.3 percentage points, the labor market is adjusting — firms are slowing hiring, reducing hours, and deferring expansion. The adjustment is reversible. When unemployment rises by 0.5 percentage points, the adjustment has become self-reinforcing: laid-off workers reduce spending, which reduces revenue for the businesses that employ other workers, which triggers additional layoffs. The 0.50-point threshold marks the transition from adjustment to contagion.
The Historical Record
The Sahm Rule triggered at the onset of every recession since 1970: the recessions of 1973-75, 1980, 1981-82, 1990-91, 2001, 2007-09, and 2020. In each case, the trigger occurred within three months of the recession's officially designated start date as determined by the National Bureau of Economic Research. In most cases, it triggered within one month.
The rule's value is timeliness. The NBER's Business Cycle Dating Committee — the official arbiter of recession start and end dates — typically announces the beginning of a recession six to twelve months after it has started. The Sahm Rule announces it in real time, using data available on the first Friday of every month. For policymakers who need to deploy fiscal stimulus, for investors who need to adjust portfolios, and for businesses who need to make hiring decisions, the difference between a twelve-month delay and a real-time signal is the difference between response and reaction.
The 2024 Near-Trigger and Its Implications
In July 2024, the three-month average unemployment rate rose to 4.13 percent — exactly 0.50 percentage points above its twelve-month low of 3.63 percent. The rule technically triggered. Economists debated whether the signal was genuine or distorted by immigration-driven labor force expansion that increased the denominator (more people seeking work) without reflecting the demand-side deterioration that characterizes a genuine recession.
Sahm herself cautioned that the rule is a statistical regularity, not a law of physics, and that structural changes in labor force composition could produce a false signal. The debate illuminated an important limitation: the rule was calibrated on fifty years of data in which labor force growth was relatively stable. A surge in immigration-driven labor supply that raises the unemployment rate through supply expansion rather than demand contraction represents a structural break that the rule's historical calibration does not account for.
The episode did not invalidate the rule. It refined the investor's understanding of it. The Sahm Rule is a necessary but not sufficient condition for recession identification. When it triggers, the burden of proof shifts — the default assumption becomes that a recession is underway unless evidence of a benign structural explanation (labor force expansion, statistical anomaly) is compelling enough to override the historical pattern.
How to Use the Sahm Rule as an Investor
The investor should monitor the Sahm Rule indicator monthly — the Federal Reserve Bank of St. Louis publishes the real-time value in its FRED database (series SAHMREALTIME). When the indicator approaches 0.40 percentage points, the probability of a trigger within the next two to three months rises significantly, and the investor should begin evaluating defensive positioning: reducing cyclical equity exposure, increasing Treasury and investment-grade bond allocations, and building cash reserves.
When the indicator crosses 0.50, the historical pattern suggests that equity markets will decline 15 to 30 percent from their prior peak over the subsequent six to twelve months, that the Federal Reserve will begin cutting rates within one to two meetings, and that corporate earnings will contract for two to four quarters. These are historical averages, not guarantees — but the consistency of the pattern across seven distinct recessions spanning fifty years provides a statistical foundation that few other indicators match.
The Sahm Rule is not a trading signal. It is a regime indicator — a binary switch that distinguishes between an economy that is cooling and an economy that is contracting. The difference between those two states is the difference between a market correction and a bear market, between a hiring slowdown and a layoff cycle, between a monetary policy hold and a monetary policy reversal. The investor who monitors the switch sees the regime change in real time. The investor who does not sees it in the rearview mirror.