Interest Rate Corridor

An interest rate corridor is a band established by a central bank using standing deposit and lending facilities to contain overnight market interest rates within a target range, effectively setting a floor and ceiling for short-term money market rates.

Why corridors matter for policy

The Federal Reserve and other central banks do not directly control the federal funds rate—the rate banks charge each other for overnight lending. Instead, they set a policy rate (currently called the target range, e.g., 4.50–4.75%) and use a corridor to keep market rates inside that band. The corridor works through incentives: if overnight rates are too high, banks have an incentive to deposit excess cash at the Fed’s standing facility (earning the floor rate), which pulls market rates down. If rates are too low, banks borrow at the ceiling, pushing rates up. This mechanical floor and ceiling keeps rates roughly where the Fed wants them.

The floor: overnight reverse repo and deposit rates

The lower bound of the corridor is set by the standing deposit facility rate, where banks can park cash overnight at the Fed. If the market overnight rate drops below the Fed’s deposit rate, banks simply deposit the cash with the Fed instead of lending it out, so the market rate cannot fall below that floor. In recent years, the Fed has also used the reverse repo facility (where eligible counterparties deposit Treasury securities and receive cash overnight), which serves a similar function. A bank holding excess cash overnight will not lend it out at 2% if it can earn 2.5% from the Fed’s standing deposit facility.

The ceiling: the discount window

The upper bound is the discount window rate, also called the primary credit rate. Banks facing a shortfall of reserves can borrow directly from the Fed’s discount window at this rate. If the market overnight rate climbs above the discount window rate, a bank needing overnight funding will simply borrow from the Fed rather than pay a higher market rate. The ceiling is thus a backstop: market rates cannot sustainably exceed the discount rate, because banks can always access funding at that rate.

Targeting the policy rate

Between the floor and ceiling sits the target rate (or target range). The Fed aims for the federal funds rate to trade around this midpoint. The width of the corridor—the spread between floor and ceiling—depends on the Fed’s design. Some central banks use a wider corridor (100+ basis points), while others use a tighter one. A narrower corridor requires more active Fed operations (open market operations, reserve management) to keep rates centered. A wider corridor is more passive but gives less precise control.

How the corridor stabilized during quantitative easing

During the 2008–2009 financial crisis and again in 2020, the Fed slashed the policy rate to near zero. At the same time, it flooded the banking system with reserves through quantitative easing (buying longer-term bonds). Abundant reserves can push overnight rates below the Fed’s target if not managed carefully. To keep the Fed funds rate from dropping too far, the Fed raised its standing deposit rate (now called Interest on Excess Reserves, or IOER) to anchor the floor. This prevented a collapse in overnight rates despite massive reserve injection. The corridor became especially important: with zero rates and huge reserves, the Fed’s facilities were the only tool keeping the policy rate from falling into negative territory.

Global variations: ECB and Bank of England

The European Central Bank and Bank of England use similar corridor systems. The ECB’s corridor is bounded by the marginal lending facility (ceiling) and the deposit facility rate (floor), both set 50 basis points away from the main policy rate. This symmetric corridor is tighter than the Fed’s, giving the ECB more precise control. During periods of abundant liquidity (post-quantitative easing), the floor rate becomes the binding constraint, and the market overnight rate (EONIA, now ESTER) trades around that floor.

Implications for money markets and spreads

The corridor structure affects money market behavior and spreads. When the corridor is wide, there is more “wiggle room” for rates to move, and spreads can widen. When the corridor is tight, money market spreads compress because market rates cannot deviate far from the boundaries. During liquidity crises, the corridor can fail to contain rates if banks are unwilling to lend or access facilities; this is why the Fed introduced emergency lending facilities during 2008–2009 and 2020. The corridor is a peacetime tool; wartime crises require more aggressive intervention.

Rate corridors and forward guidance

The width and position of the corridor can signal the Fed’s policy stance. A wide corridor and a low target range signal ease. A narrow corridor and high target range signal tightness. The corridor also interacts with forward guidance: if the Fed commits to keeping rates low for an extended period, it also commits to keeping the corridor’s floor low, anchoring longer-term rate expectations.