When a central bank changes its policy rate, the announcement is immediate and the effect on households is anything but. The transmission takes months, arrives unevenly, and is substantially weaker in some economies than others for reasons that come down to the structure of the mortgage market rather than to monetary policy itself.
The rate that is actually set
A central bank does not set mortgage rates, savings rates, or business lending rates. It sets a very short-term rate — typically the rate paid on commercial bank reserves held at the central bank, or the rate at which it lends to banks overnight. Everything else is a market response to that anchor.
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The mechanism works because that overnight rate defines the opportunity cost of every other use of a bank’s money. If a bank can earn a guaranteed return by leaving funds at the central bank, it will not lend at less than that plus compensation for risk and term.
From overnight to the yield curve
The first link is the money market, where the policy change passes almost immediately into overnight and short-term interbank rates. The second and more interesting link is the yield curve — the structure of interest rates across different maturities.
Longer-term rates reflect expectations of where short rates will be over the life of the instrument, plus a term premium compensating for uncertainty. This is why a rate rise that markets fully anticipated can leave long-term rates unchanged or even lower them: the expectation was already priced in, and if the accompanying communication suggests fewer future rises than expected, longer rates fall.
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The practical consequence is that what a central bank says about the future path frequently matters more for mortgage costs than what it does today. Fixed-rate mortgages are priced off swap rates and government bond yields at matching maturities, not off the overnight rate.
Why market structure determines everything
The transmission to households depends overwhelmingly on what kind of mortgages a country’s borrowers hold.
Where variable-rate mortgages dominate, transmission is fast and powerful. A policy change reaches monthly payments within one or two billing cycles, and household cash flow responds almost immediately. Monetary policy in such economies is a blunt and effective instrument.
Where long-term fixed rates dominate, transmission is slow and partial. Existing borrowers are insulated entirely until their deal expires. The policy change affects only new borrowers and those refinancing, which in any given year is a modest fraction of the stock. The full effect can take five years or more to work through, and a large share of it never arrives at all if rates move back before deals mature.
Many economies sit between these poles with short-term fixes of two to five years, producing a rolling reset in which a predictable slice of borrowers moves onto new rates each quarter. This creates the phenomenon sometimes called the mortgage cliff — a concentrated wave of payment increases arriving well after the policy decisions that caused them.
The bank margin
Banks do not pass changes through mechanically. Between the policy rate and the mortgage rate sits a margin covering funding costs, expected credit losses, capital requirements and profit. That margin widens and narrows with competitive conditions and with perceived risk.
A well-documented asymmetry exists here: increases in policy rates tend to reach borrowers faster than they reach savers, and decreases reach borrowers more slowly than they reach savers. The effect is modest but persistent, and it is one reason bank net interest margins typically improve in a rising rate environment.
The other channels
Mortgages are the most visible channel but not the only one. Asset prices respond, since higher discount rates lower the present value of future cash flows, which affects equity and property valuations and through them household wealth and spending. Exchange rates respond, since higher relative returns attract capital, and a stronger currency lowers import prices — a channel that works considerably faster than the credit channel.
Business investment responds too, though evidence suggests corporate capital spending is less sensitive to the cost of borrowing than to expected demand, which is why rate cuts alone often disappoint as a stimulus.
The lag, and why it matters
Conventional estimates put the peak effect of a rate change on inflation somewhere between twelve and twenty-four months out. That lag is the central difficulty of monetary policy: decisions must be made on forecasts, and by the time the effect is visible the appropriate setting may have changed.
It also explains a pattern that regularly frustrates observers — a central bank continuing to hold rates high while inflation is visibly falling. The committee is not responding to today’s data but to where it expects inflation to be when today’s decision actually bites.
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Sources and further reading
- Bank of England — Bank Rate — what the rate is and how it is set
- Financial Conduct Authority — the rules lenders must follow on affordability and disclosure
