Sahm Rule

What Is the Sahm Rule?

The Sahm Rule is the most precise and practical recession indicator in the modern macro trader's toolkit, a simple, elegant formula that has correctly identified every US recession since 1970 with no false positives (through 2019). Developed by economist Claudia Sahm during her time at the Federal Reserve Board, the rule provides a real-time signal that a recession has begun, months before the NBER officially declares one and before two consecutive quarters of negative GDP can confirm it.

The rule states: 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 prior 12 months, the economy is in recession.

This simple formula moved global markets in August 2024, when its triggering produced the most violent single-week market event since the COVID crash: the VIX spiked to 65, the S&P 500 fell 6%, and the yen carry trade unwound catastrophically. The episode demonstrated both the Sahm Rule's enormous influence and its limitations, making it essential reading for any serious trader.

The Formula

Sahm Rule Indicator = 3-Month Average Unemployment Rate − Minimum(3-Month Average Unemployment Rate over prior 12 months)

Trigger threshold: ≥ 0.50 percentage points

Worked Example

Suppose the monthly unemployment rates for the past 15 months are:

• Current 3-month average (Jan-Mar Y): 3.93%
• 12-month low of 3-month average (Apr Y-1 to Mar Y): 3.43% (May-June Y-1)
• Sahm Rule reading: 3.93% − 3.43% = 0.50% → TRIGGERED

Historical Performance

Perfect Accuracy Through 2019

*The 1973-75 trigger was late because unemployment rose slowly initially, but once it triggered, the recession was already well underway.

The average lag is approximately 2-3 months after the recession's official start, meaning the Sahm Rule typically identifies a recession that is already underway. This is earlier than the NBER declaration (which often comes 6-12 months after the recession starts) and earlier than the "two quarters of negative GDP" rule (which requires at least 6 months of data).

The 2024 Controversy

In July 2024, the Sahm Rule reading reached 0.53%, above the 0.50% threshold, as the 3-month average unemployment rate rose from its 2023 low of 3.43% toward 4.0%.

What made 2024 different:

1. Supply-driven unemployment: The rise was driven by an expanding labour force (immigration + rising participation) rather than by layoffs. More people entering the labour force mechanically raises the unemployment rate even if job creation continues.
2. Low initial claims: The 4-week average of initial jobless claims remained near 230K, well below the ~300K level associated with prior Sahm Rule triggers during actual recessions.
3. Strong GDP: Real GDP was growing above 2% annualised, inconsistent with recession.
4. The creator's disclaimer: Claudia Sahm publicly stated the indicator might be giving a "false signal" given the unique post-pandemic labour market dynamics.

Market reaction: Despite these caveats, the trigger produced a historic market event. The August 5, 2024 selloff saw the VIX reach 65 intraday (the highest since March 2020), S&P 500 futures fell 4% overnight, and the yen carry trade, which had accumulated enormous leveraged positions, unwound violently as traders rushed to de-risk.

Resolution: By September 2024, it became clear the trigger was indeed a false signal. Unemployment stabilised near 4.2%, initial claims remained low, and GDP continued growing. The S&P 500 recovered its losses within three weeks.

Why the Sahm Rule Works (Usually)

The Labour Market Momentum Logic

The rule captures a fundamental asymmetry in labour market dynamics:

• During expansions: Unemployment falls slowly (firms hire gradually, one position at a time). The decline is typically 0.2-0.3 percentage points per year.
• During recessions: Unemployment rises rapidly (mass layoffs occur in waves as businesses retrench simultaneously). The increase is typically 1-3 percentage points over 6-12 months.

The 0.5 percentage point threshold identifies the moment when the unemployment increase has exceeded normal fluctuation and entered the "mass layoff" acceleration phase. Once this threshold is crossed, the momentum is typically self-reinforcing: layoffs → reduced consumer spending → more layoffs → further spending cuts.

Why 0.50 and Not Some Other Number?

Sahm calibrated the threshold by examining every post-war business cycle:

• 0.30: Too sensitive, would have generated false positives in 1976, 1986, and 2003
• 0.40: Slightly better but still false positive-prone
• 0.50: The Goldilocks threshold, triggered during every recession without any false positives (through 2019)
• 0.60+: Would have missed the start of several recessions, reducing the indicator's timeliness

Combining the Sahm Rule with Other Indicators

The Sahm Rule is most valuable when used as part of a recession indicator cluster:

The cluster approach:

• 1-2 indicators flashing: Elevated risk; reduce cyclical exposure at the margin
• 3-4 indicators flashing: High recession probability; shift to defensive positioning
• 5-6 indicators flashing: Recession almost certain; maximum defensive positioning (long duration, cash, gold)

The 2024 Sahm Rule trigger was accompanied by only 1-2 other indicators (yield curve had already un-inverted, ISM manufacturing was weak but services held, claims were low). This cluster analysis correctly suggested the Sahm Rule was giving a false positive.

Trading the Sahm Rule

Pre-Trigger Zone (Reading 0.30-0.49)

When the Sahm Rule reading is approaching but hasn't reached the threshold:

At Trigger (Reading ≥ 0.50)

If confirmed by claims + ISM:

• Maximum defensive: underweight equities, overweight Treasuries, add gold
• Short cyclicals vs. long defensives (XLI/XLY vs. XLU/XLP)
• Long 2Y Treasuries (aggressive rate cuts will be priced in)

If NOT confirmed by claims + ISM:

• Hold current positions; don't panic
• Watch for the Sahm Rule reading to stabilise or reverse
• The 2024 template: false signal → rapid V-shaped equity recovery → buying opportunity

The Post-Trigger Trading Opportunity

If the Sahm Rule triggers and the market panics (as in August 2024), but other indicators don't confirm:

• Buy the dip aggressively in equities (especially quality growth)
• Sell volatility after the VIX spike (VIX above 40 + no fundamental recession = vol selling opportunity)
• Fade the rate cut pricing if the economy is actually fine (front-end Treasuries may have overshot)

What to Watch

1. FRED SAHMREALTIME: The official real-time Sahm Rule reading, updated monthly on NFP day. Set an alert for readings above 0.35.
2. Monthly NFP unemployment rate: The input data. Watch for month-over-month increases in unemployment of 0.2%+, that pace leads to Sahm Rule triggering within 2-3 months.
3. Initial jobless claims: The confirmation variable. If the Sahm Rule triggers but claims stay below 230K, the signal is likely false.
4. Labour force participation rate: Distinguish supply-driven unemployment increases (more people looking = less alarming) from demand-driven (layoffs = very alarming).
5. Continuing claims: The total number of people receiving unemployment benefits. A sustained rise above 2 million signals the labour market is deteriorating, not just normalising.