<P> Zero interest - rate policy (ZIRP) is a macroeconomic concept describing conditions with a very low nominal interest rate, such as those in contemporary Japan and December 2008 through December 2015 in the United States . ZIRP is considered to be an unconventional monetary policy instrument and can be associated with slow economic growth, deflation, and deleverage . </P> <P> Under ZIRP, the central bank maintains a 0% nominal interest rate . The ZIRP is an important milestone in monetary policy because the central bank is no longer able to reduce nominal interest rates--it is at the zero lower bound . Conventional monetary policy is at its maximum potential to drive growth under ZIRP . ZIRP is very closely related to the problem of a liquidity trap, where nominal interest rates cannot adjust downward at a time when savings exceed investment . </P>

When did the fed lower interest rates to zero