Why Is There a “Zero Lower Bound” on Interest Rates?

Todd Keister

Economists often talk about nominal interest rates having a “zero lower bound,” meaning they should not be expected to fall below zero. While there have been episodes—both historical and recent—in which some market interest rates became negative, these episodes have been fairly isolated. In this post, I explain why negative interest rates are possible in principle, but rare in practice. Financial markets are generally designed to operate under positive interest rates, and might experience significant disruptions if rates became negative. To avoid such disruptions, policymakers tend to keep short-term interest rates above zero even when trying to loosen monetary policy in other dimensions. These policy choices are the source of the zero lower bound.

    The standard description of the zero lower bound begins with the observation that the nominal interest rate offered by currency is always zero: If I hold on to a dollar bill, I’ll still have one dollar tomorrow, next week, or next year. If I invest money at an interest rate of -2 percent, in contrast, one dollar of saving today would become only ninety-eight cents a year from now. Because everyone has the option to hold currency, the argument goes, no one would be willing to hold some other asset or investment that offers a negative interest rate.

    This argument is only part of the story, however. Safeguarding and transacting with large quantities of currency is costly. One only needs to imagine the risk and hassle of making all transactions in cash—paying the rent or mortgage, utility bills, etc.—to appreciate the safety and convenience of a checking account. Many individuals would likely be willing to keep funds in deposit accounts even if these accounts pay a negative interest rate or charge maintenance fees that make their effective interest rate negative.

    Large institutional investors are in a similar situation. They use a variety of short-term investments, such as lending funds in the “repo” (repurchase agreement) market and holding short-term Treasury bills, in much the same way individuals use checking accounts. These investments will remain attractive to large investors even at negative interest rates because of the security and convenience they offer relative to dealing in currency. Some repo rates did in fact become negative in 2003 (see this New York Fed study) and again more recently (see Bloomberg). Interest rates in the secondary market for Treasury bills have also been slightly negative recently (see Businessweek).

    In other words, market interest rates can move somewhat below zero without triggering a massive switch into currency. Nevertheless, central banks typically maintain positive short-term interest rates even while using less conventional tools (such as large-scale asset purchases) to provide additional monetary stimulus.

    The Federal Reserve, for example, currently pays an interest rate of 0.25 percent on the reserve balances that banks hold on deposit at the Fed. The ability to earn this interest gives banks an incentive to borrow funds in a range of markets (including the interbank market and the repo market) and thus has the effect of keeping market interest rates positive most of the time. The Federal Open Market Committee (FOMC) discussed the idea of reducing the interest on reserves (IOR) rate at its September meeting, but no action was taken. Reducing this rate would tend to lower short-term market interest rates and might push some rates below zero. The minutes from the meeting report that “many participants voiced concerns that reducing the IOR rate risked costly disruptions to money markets and to the intermediation of credit, and that the magnitude of such effects would be difficult to predict.”

    Similarly, the Monetary Policy Committee (MPC) of the Bank of England discussed the possibility of lowering the official Bank Rate below 0.5 percent at its September meeting, but decided against doing so. The MPC had previously expressed concern that “a sustained period of very low interest rates would impair the functioning of money markets.”

    Some examples of areas where disruptions could potentially arise in U.S. financial markets are:

• Money market mutual funds: Money market funds operate under rules that make it difficult for them to pay negative interest rates to their investors, either directly or by assessing fees. Many of these funds would likely close down if the interest rates they earn on their assets were to fall to zero or below, possibly disrupting the flow of credit to some borrowers.
• Treasury auctions: The auction process for new U.S. Treasury securities does not currently permit participants to submit bids associated with negative interest rates. If market interest rates become negative, new Treasury securities would be issued with a zero interest rate—effectively a below-market price—and bids would be rationed if demand exceeds supply. Such rationing, which has occurred in recent auctions, would generate an incentive for auction participants to bid for more than their true demand, leading to even more rationing. This situation could generate market volatility, as unexpected changes in the amount of rationing in each auction could leave some investors holding either many more or many fewer securities than they desire.
• Federal funds: A decrease in the IOR rate would also likely affect the federal funds market, where banks and certain other institutions lend funds to each other overnight. A lower IOR rate would give banks less incentive to borrow in this market, which would likely decrease the amount of activity. When less activity takes place, the market interest rate will be influenced more by idiosyncratic factors, making it a less reliable indicator of current conditions. This decoupling of the federal funds rate from financial conditions could complicate communications for the FOMC, which operates monetary policy in part by setting a target for this rate.

    These examples demonstrate that many current institutional arrangements were not designed with near-zero or negative interest rates in mind. In principle, these arrangements—such as the rules governing mutual funds and Treasury auctions—could be changed. The implementation of a “fails charge” in 2009 for the settlement of Treasury securities (see this New York Fed study) is one example of an institutional adaptation that allows markets to function better at very low interest rates. (A similar charge is scheduled to take effect in some mortgage-related markets in February 2012.) In practice, however, such changes may take significant time to implement and could simply move disruptions to other markets.

    Given the markets’ limited experience with very low interest rates, it is difficult to predict with any degree of certainty how they will react to them. If the types of disruptions described above turn out to be significant, taking steps to lower short-term interest rates could actually make financial conditions tighter rather than looser and thus hinder the economic recovery. To avoid this outcome, policymakers tend to choose policies that keep market interest rates positive. In other words, the potential for negative interest rates to disrupt financial markets limits the extent to which policymakers can stimulate economic activity by lowering interest rates. This limit is known as the zero lower bound.

Disclaimer
The views expressed in this blog are those of the author and do not necessarily reflect the position of the Federal Reserve Bank of New York, or the Federal Reserve System. Any errors or omissions are the responsibility of the author.