A mortgage quote helps explain why four central banks can move differently and why their decisions are only part of the story

By Dr Laurin Lilly-Laona Friedrich

The Bank of England leaves its rate unchanged. A household opening a mortgage renewal quote may still find that its budget is about to change.

On 17 September, the Bank held Bank Rate at 3.75%, by six votes to three. Yet quoted two-year fixed mortgage rates were already around 0.95 percentage points above their level before the Middle East conflict. That describes the price of a new deal; each borrower’s experience depends on the deal they are leaving and when it ends.

The following day, the Bank of Japan voted seven to two to raise its short-term policy rate from around 1% to around 1.25%, effective 24 September. It nevertheless judged that financial conditions would remain accommodative.

An unchanged rate alongside tighter borrowing conditions. A higher rate alongside continuing support. Both make sense once we follow the announcement into the economy it is meant to influence.

What is a rate change trying to change?

For the household looking at its renewal quote, the immediate question is how much money will remain after the mortgage payment. That ordinary calculation is part of why central banks use interest rates in the first place.

Changing the cost of short-term money influences borrowing, saving and spending. Higher rates generally make new borrowing less attractive and saving more rewarding. As loans reprice, some borrowers have less to spend elsewhere. Firms may postpone investments that no longer earn enough to justify their financing costs. Together, these adjustments can moderate demand and ease inflation pressure; lower rates can support activity when demand is weak. The effects arrive unevenly and with a delay.

But an interest rate cannot reopen a shipping route or produce more fuel. An energy shock makes life more expensive while also squeezing the money available for other purchases. The policy question becomes how much inflation will persist and how much additional restraint the economy can bear.

The ECB’s 10 September increase, which took its deposit rate to 2.50%, reflected concern that energy-related inflation pressure would endure. Its inflation projections for 2027 and 2028 had risen. On 16 September, the Federal Reserve raised its target range to 3.75–4.00% against a different backdrop: elevated inflation alongside resilient spending and robust investment. Each increase was a quarter of a percentage point. The conditions it was intended to influence were different.

Japan makes that distinction particularly clear. The BoJ saw underlying inflation approaching 2%, with firms increasingly passing wage costs into prices. For Japan, the question was whether wage growth and price-setting would sustain inflation around 2%. For the ECB and Fed, inflation was already above the level they wanted to restore. Even after its rise, the BoJ considered real interest rates low. These reflect the cost of money after allowing for expected inflation: the nominal rate alone does not tell us how much restraint policy exerts.

How much has changed before the announcement?

That leaves an important question for the committee deciding whether to act: how much adjustment is already under way?

A fixed mortgage quote reflects more than today’s central-bank rate. The expected path of future policy affects longer-term market rates and lenders’ funding costs. Pricing also includes compensation for risk. Borrowing can therefore become more expensive before a committee votes to raise its rate—and a higher market rate need not be a pure forecast of what that committee will do.

The UK provides a live example. Market repricing had been under way since the conflict began. Most members of its Monetary Policy Committee judged the existing restraint broadly sufficient, alongside soft labour conditions and limited evidence of energy costs feeding into wages and wider pricing. Those favouring an increase were less reassured about inflation risks. Some also warned that risk premia could reverse unpredictably. The dispute concerned both the durability of existing restraint and the pressure still to come.

Anticipation has practical consequences whether or not the anticipated decision arrives. A company may have deferred an investment; a buyer may have reduced a housing budget. A subsequent hold does not automatically undo either choice.

Following those choices brings us to a question at the heart of LUNÆOS: how do people make sense of changed conditions, and what does that understanding lead them to do? The mortgage quote gives us somewhere concrete to begin.

What does the same quote mean to different people?

Expectations enter this story twice. They help shape the price a lender offers. They also provide a comparison against which the borrower judges it.

First, however, there is a budget. Someone who cannot meet the new payment faces a material constraint, whatever they expected. Someone whose fixed deal continues for another year may have time to prepare. The date at which a changed rate reaches a household matters as much as the date on the announcement.

Now imagine two households with similar finances, both able to afford the same new quote. One had expected a cheaper mortgage; the other had prepared for a much worse renewal. The quote can disappoint the first and relieve the second, although it asks the same amount of money from each. Does that difference affect their willingness to commit to a purchase both can still afford?

Kahneman and Tversky’s work on reference-dependent choices offers a way to investigate this: people can evaluate outcomes as gains or losses relative to a reference point, including an expectation. It makes that comparison worth examining. It does not establish which household will spend more, or whether a difference would reflect that reference point rather than a different forecast of future costs.

Will the planned purchase survive? Will they draw on savings, reduce spending immediately or retain a larger buffer because they expect further pressure? Beliefs about the duration of the squeeze matter here, too. The new payment changes what is affordable; the household must still decide what to protect, postpone or give up.

What should we do with that understanding?

Those decisions become someone else’s trading conditions. A business considering a price increase needs to know how much room its customers have to absorb it. A firm expecting demand to recover after a policy hold may be disappointed. Even if new mortgage quotes stop rising, customers leaving older, cheaper deals can still face higher payments.

For a leader assessing an investment or sales plan, this suggests a specific challenge to the assumptions: when will changed financing costs reach the borrowers whose decisions the plan depends on? A forecast that translates a policy announcement straight into stronger demand leaves out the contracts, renewal dates and spending choices through which that effect would have to occur.

It also helps to ask what customers had already counted on, and how secure they now feel about spending. Their answers help us understand the choices still ahead. Their actual purchases, alongside firms’ investment and pricing decisions, will contribute to the evidence central banks assess over the months that follow.

When the next headline says “hold” or “hike”, follow it to an actual decision: whose costs are changing, when must they respond, and what can they still choose?

Decisions and information as of 18 September 2026. The household comparisons are illustrative.