Economy · Explainer
How a central bank actually sets the interest rate
A policy rate is not imposed on lenders. It is engineered through the market for reserves, and it transmits unevenly.
The short answer
- Policy rates work by setting the return on central bank reserves.
- Transmission to households and firms runs through bank funding and expectations.
- The lag between a decision and its effect is measured in quarters, not weeks.
A central bank does not instruct commercial banks what to charge. It sets the terms on which banks can hold reserves with it and borrow from it, and those terms anchor the shortest, safest rate in the system. Every other rate is priced relative to that anchor plus a margin for term, credit and liquidity.
The floor system
Where reserves are plentiful, the rate paid on them sets a floor: no bank lends to another below the risk-free return it can earn by doing nothing. A standing lending facility sets a ceiling. The policy rate lives between them, and open market operations keep it there.
Transmission is the hard part
- Bank funding costs move, then loan and deposit pricing follows — at different speeds.
- Asset prices reprice immediately, changing wealth and collateral values.
- Exchange rates adjust, feeding into import prices.
- Expectations of future policy shape long rates more than today's decision does.
Lags and the credibility problem
Because the effects arrive with long and variable lags, policy has to be set against a forecast. That forces central banks into a communication problem: they must sound certain enough to anchor expectations while being honest that the forecast will be wrong in detail.
Sources
- How monetary policy works — Federal Reserve
- Monetary policy instruments — European Central Bank
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