Rates move in quarter points, and nobody can picture a quarter point. Here is the same movement in the currency a buyer understands: floor area.
What matters is not the rate but what it lets you borrow
Work forwards from the payment, never backwards from the price. What a household can commit to every month is fixed, and a lender will stress-test it against a higher rate than the one on the offer. Hold the payment still and the rate decides the rest.
At the same monthly payment, a higher rate means a bigger share of it is interest, so there is less capital underneath. That is the whole mechanism, and why a quarter point that looks trivial on a rate sheet removes a real slice of what you can buy.
Two caveats before the maths is used. It holds one rate for the whole term, an assumption rather than a description of the British market, where a two or five year fix reverts to a variable rate. And it is capital only: no product fees, no deposit, no stamp duty, no survey.
One point, priced in pounds
Take a household paying £1,200 a month over 25 years, and change nothing but the rate.
A full point between 4% and 5% takes £22,071 off what the bank will advance for exactly the same money every month, which at £3,000 per square metre is 7.4 m². The house got no more expensive; the buyer got smaller. Quarter by quarter it is roughly £5,500 and just under two square metres a time, a box room, or the difference between a galley kitchen and one you can eat in.
Turning pounds into square metres, honestly
The £3,000 in the table is a round illustration, not a national statistic. The headline series published here, the UK House Price Index, is an average price per property, not a price per square metre, and dividing it by an assumed house size produces a number that looks official and is not.
So do it on the street you are buying in. Take three asking prices for the property you want, look up each address on the free energy performance certificate register, which gives the total floor area in square metres, divide, and take the middle one. That price per square metre applies to your search rather than to the country.
It is the third input, alongside the payment you can sustain and the term a lender will grant. Take all three from your own situation and the answer stops being an illustration. How much you can borrow is the same arithmetic run from the other end.
The levers you can pull, when the rate is not one
Fixed rates here follow swap rates, which move with what the market expects Bank Rate to do rather than with what it does today. No buyer influences that. Four other things are within reach.
- Cross a loan-to-value band with a bigger deposit: lenders price in steps at 90%, 85%, 80% and 75%, and one band down can beat waiting a quarter for the market to soften.
- Stretch the term: 30 years instead of 25, at 4% and the same £1,200 a month, adds about £24,000 of borrowing, and five more years of interest. It buys capacity, not value.
- Read the fee, not just the rate: a headline rate with a four-figure product fee behind it is often beaten by a slightly higher rate with none, especially on a smaller loan.
- Put the same case to several lenders, through a broker or directly: the spread between best and worst answer on one file regularly exceeds the half point everyone is worrying about.
One lever exists only if you already own something: carrying your current deal to the next property instead of surrendering it. That has its own traps, covered in porting a mortgage to a new house.
Wait for a better rate, or buy now
Half a point on the rate costs about 5% of your borrowing power; a 1% fall in prices gives you back 1%. It takes a serious correction in the street you are watching to beat a rate move of that size.
The other half of the trade-off has a clock on it. A mortgage offer holds for months, not indefinitely, and an agreement in principle expires sooner still, so a buyer who freezes often redoes the whole exercise at the newer, worse rate.
- Do not compare two offers on the monthly payment alone: the same payment can advance tens of thousands more or less, and the term is usually the reason.
- Do not price your search off a national average, because the figure that decides your floor area comes from the postcode you are bidding in.
- Do not sit on an agreement in principle: it lapses, and the file is re-underwritten at whatever is on the shelf that week.
Shopping the same case around, and pushing the deposit over the next band, beats trying to time a market nobody in it can predict. Both are available this week.