Zero Lower Bound

The zero lower bound (ZLB) is the macroeconomic constraint that nominal interest rates cannot be reduced below zero — or slightly below zero, in economies with negative rate experiments — because cash provides a risk-free nominal return of zero. When a central bank hits the ZLB, conventional monetary policy loses its primary tool: the ability to stimulate demand by lowering short-term interest rates. The constraint became central to macroeconomic policy after 2008, when the Federal Reserve, the European Central Bank, and the Bank of Japan all found their policy rates at or near zero despite persistent economic weakness.

The ZLB is not merely a technical constraint on central bank operations. It is a structural feature of monetary economies that use cash as a liability-free store of value. As long as cash exists, no central bank can push nominal rates significantly negative without triggering a flight to physical currency. This creates an asymmetry in monetary policy: there is no upper limit on how high rates can go, but there is a hard floor at zero. The asymmetry implies that deflationary shocks are harder to combat than inflationary shocks, and that economies near the ZLB are operating with one policy arm tied behind their backs. The experience of Japan since the 1990s demonstrates that the ZLB is not a temporary liquidity trap but a potentially permanent feature of aging, low-growth economies.