Zero Lower Bound

The zero lower bound (ZLB) refers to the practical floor on nominal interest rates near 0%. The logic is straightforward: if a central bank tried to push short-term rates deeply negative, depositors and banks would prefer to hold physical cash (which yields 0%) rather than pay to keep money in accounts or bonds. This creates an effective floor that constrains conventional monetary policy, since central banks normally fight recessions by cutting their policy rate.

The ZLB became a central concern in advanced economies after the 2008 global financial crisis. The U.S. Federal Reserve cut its federal funds target to a range of 0–0.25% in December 2008 and held it there for seven years. The Bank of England, Bank of Japan, and European Central Bank faced similar binding constraints. With no room to cut further, central banks turned to unconventional tools:

• Quantitative easing (QE): large-scale purchases of government bonds and other assets to lower long-term yields.
• Forward guidance: explicit communication about the expected future path of rates to shape market expectations.
• Negative interest rate policy (NIRP): charging banks for excess reserves, adopted by the ECB (2014), Bank of Japan (2016), and the Swiss National Bank, among others. This showed the lower bound is slightly below zero in practice—sometimes called the effective lower bound (ELB)—but storage and conversion costs for cash still impose a limit.

Economists including Paul Krugman, Michael Woodford, and Ben Bernanke have written extensively on ZLB dynamics, often linking them to Keynes's idea of a liquidity trap. Policy debates around the ZLB have influenced proposals to raise inflation targets, adopt average inflation targeting (which the Fed formally did in August 2020), or use fiscal policy more aggressively when monetary policy is exhausted.

The constraint matters for IR and political-economy analysis because it shifts the burden of stabilization toward fiscal authorities and reshapes debates over central bank independence, sovereign debt, and international policy coordination.