What is the inventory cycle?

The inventory cycle, sometimes called the Kitchin cycle after economist Joseph Kitchin, describes the periodic buildup and liquidation of business inventories that amplifies fluctuations in GDP growth. Companies hold inventories as a buffer to meet customer demand, but the process of building and reducing those buffers creates its own economic dynamics that are distinct from underlying demand trends.

When businesses expect demand to grow, they increase production above current sales to build inventory stocks, adding to GDP growth beyond what final demand alone would generate. This "inventory accumulation" phase adds roughly 0.5-1.0 percentage points to GDP growth in a typical expansion. When businesses sense that demand is weakening, they cut production below current sales to reduce bloated inventories, subtracting from GDP growth. This "inventory liquidation" phase can shave 1-2 percentage points off GDP during downturns.

The amplification effect is significant. In the typical recession, inventory liquidation accounts for roughly one-third of the GDP decline, even though inventories represent only a small share of the total economy. The mechanism is self-reinforcing: when businesses cut orders to reduce inventory, their suppliers experience a demand drop, which causes the suppliers to cut production and lay off workers, reducing income and spending, which further weakens the final demand that triggered the inventory reduction in the first place.

The inventories-to-sales ratio is the primary metric for tracking where the economy sits in the inventory cycle. A rising ratio suggests that inventories are growing faster than sales, indicating that businesses may need to cut production (bearish for GDP). A falling ratio suggests that sales are outpacing inventory accumulation, meaning businesses may need to ramp up production to restock (bullish for GDP). The ratio spiked during the COVID supply chain crisis as companies panic-ordered to build buffers, then the subsequent normalization of inventories contributed to the manufacturing slowdown of 2022-2023.