How mortgage rates distort affordability metrics

When the Bank of England base rate sat at 0.1% in late 2021, a couple earning £60,000 combined could borrow roughly £270,000 on a typical mortgage.

By autumn 2023, with rates above 5%, that same couple's borrowing capacity had dropped to around £225,000—a £45,000 reduction despite identical incomes.

Yet most affordability indices continued reporting house prices as "8.5 times earnings" without acknowledging that the cost of servicing that debt had nearly doubled.

This disconnect reveals a fundamental flaw in how we measure housing affordability in the UK.

Traditional metrics compare house prices to incomes, but they ignore the elephant in the room: mortgage rates determine what buyers actually pay each month, and monthly payments are what matter when you're deciding whether to stretch for that three-bed semi in Reading or settle for a two-bed flat.

Why the price-to-earnings ratio misleads

The Office for National Statistics publishes quarterly affordability ratios showing median house prices divided by median earnings.

In Q2 2024, the England-wide ratio stood at 8.8—meaning the typical home costs 8.8 times the typical annual salary.

Commentators cite this figure to argue housing has never been less affordable.

But this metric treats a £300,000 house the same way regardless of whether you're borrowing at 2% or 6%.

In reality, the monthly cost difference is enormous.

A £270,000 mortgage (90% LTV on a £300,000 property) at 2% over 25 years costs roughly £1,145 per month.

The same mortgage at 6% costs £1,740—an extra £595 monthly, or £7,140 annually.

For a household earning £60,000 gross (roughly £3,800 monthly after tax and National Insurance), that £595 difference represents 15.7% of take-home pay.

It's the difference between comfortably affording the mortgage and struggling to cover council tax, energy bills, and food.

How lenders actually assess affordability

Mortgage lenders don't care about price-to-earnings ratios.

They care about debt-to-income ratios and whether you can service the monthly payments under stress conditions.

Since the Mortgage Market Review in 2014, lenders must verify you can afford repayments even if rates rise by 3 percentage points above the initial rate.

This stress testing means that when mortgage rates climb, lenders reduce the amount they'll offer—even if your income hasn't changed.

The calculation works roughly like this:

Notice that even though the November 2024 scenario offers a lower rate than October 2023, the monthly payment on the larger loan amount is only slightly lower.

This illustrates why falling rates don't immediately restore affordability—lenders remain cautious, and the stress test still bites.

The hidden impact on first-time buyers

First-time buyers feel this distortion most acutely because they typically borrow at higher loan-to-value ratios.

Someone with a 10% deposit faces significantly higher rates than a buyer with 25% equity.

In November 2024, the difference between a 90% LTV and 75% LTV mortgage rate averaged around 0.6 percentage points—seemingly modest, but meaningful over 25 years.

Consider a first-time buyer purchasing a £250,000 property in Birmingham with a £25,000 deposit (10% LTV).

At a 90% LTV rate of 5.2%, their monthly payment is approximately £1,315.

If they could somehow scrape together a £62,500 deposit (25% LTV) and access a 4.6% rate, the payment drops to £1,040—a £275 monthly saving, or £3,300 annually.

This creates a vicious cycle.

Higher rates mean buyers need larger deposits to access better rates, but saving for larger deposits takes longer—during which time house prices may rise further, and the buyer continues paying rent that could otherwise go toward a mortgage.

Regional variations compound the problem

Affordability metrics that focus solely on price-to-earnings ratios miss how regional income variations interact with mortgage rates.

In London, where median earnings are higher but house prices are astronomical, a rate increase affects absolute borrowing capacity more dramatically than in the North East.

A London household earning £80,000 might have borrowed £360,000 at 2.5% in 2021.

At 5.5% in 2023, their borrowing capacity dropped to roughly £300,000—a £60,000 reduction.

Meanwhile, a Newcastle household earning £45,000 saw their capacity fall from £202,500 to £168,750—a £33,750 reduction.

Both households lost purchasing power, but the London buyer lost nearly twice as much in absolute terms.

Yet the price-to-earnings ratio in both regions might show similar "affordability" levels, masking the reality that higher earners in expensive regions face steeper cliffs when rates rise.

"Affordability isn't just about whether you can theoretically borrow enough to buy a house.

It's about whether you can comfortably service that debt while maintaining a reasonable standard of living, covering unexpected repairs, and saving for the future.

Mortgage rates determine all of that far more than the sticker price."

Why rental yields don't tell the full story either

Property investors face a parallel distortion.

Gross rental yields—annual rent divided by property price—are often cited as a measure of investment viability.

A property generating £12,000 annual rent with a £200,000 purchase price shows a 6% gross yield, which sounds attractive.

But if you're financing that purchase with a buy-to-let mortgage at 5.5%, your annual interest cost on a £150,000 loan (75% LTV) is £8,250.

Subtract that from the £12,000 rent, and you're left with £3,750 before accounting for maintenance, letting agent fees (typically 10-12% of rent), insurance, safety certificates, and void periods.

When buy-to-let rates sat below 3%, a 6% gross yield translated to healthy cash flow.

At 5.5%, that same yield barely covers costs.

Yet the gross yield figure remains unchanged, creating an illusion of consistent returns when the reality has shifted dramatically.

Practical framework: calculating true affordability

Rather than relying on price-to-earnings ratios, buyers and investors should calculate affordability based on actual monthly costs.

Here's a practical checklist for assessing whether a property is genuinely affordable:

• Calculate your monthly mortgage payment at the current rate, not the stress test rate
• Add £150-200 monthly for buildings insurance and life insurance
• Include council tax for the specific property (check the local authority website)
• Factor in £100-150 monthly for maintenance and repairs (more for older properties)
• If leasehold, add the monthly service charge and ground rent
• Ensure total housing costs don't exceed 35% of your net monthly income
• Verify you can still save at least £200-300 monthly for emergencies
• Check whether you'd cope if rates rose by 1-2 percentage points at remortgage time

This approach gives you a realistic picture of whether you can afford the property, not just whether a lender will approve the mortgage.

It's particularly important for buyers stretching to their maximum borrowing capacity, where even a modest rate increase at remortgage time could cause serious financial stress.

The stamp duty complication

Stamp duty adds another layer of distortion to affordability calculations.

Because it's a one-off cost paid upfront, it doesn't feature in monthly affordability metrics, yet it directly affects how much deposit you need and whether you can afford to move.

In England, a first-time buyer purchasing a £300,000 property pays no stamp duty on the first £300,000 (as of November 2024, though this threshold is scheduled to drop to £250,000 in April 2025).

A second-stepper buying the same property pays £2,500.

An investor purchasing it as a buy-to-let pays £11,500 (including the 3% surcharge).

These differences mean that affordability varies dramatically depending on your buyer status, even if your income and the property price are identical.

An investor needs an extra £9,000 upfront compared to a first-time buyer—money that could otherwise go toward a larger deposit, reducing the mortgage rate and monthly payments.

When rates are low, stamp duty is an annoyance.

When rates are high, it becomes a significant barrier because buyers are already stretching to meet deposit requirements and higher monthly payments.

The combination can price out buyers who would have been comfortably affordable in a lower-rate environment.

How to compare properties across rate environments

If you're trying to understand whether housing is more or less affordable than it was five years ago, forget price-to-earnings ratios.

Instead, compare the monthly cost of servicing a mortgage as a percentage of median income.

In 2019, the median UK house price was approximately £230,000, and the average mortgage rate was around 2.8%.

A buyer with a 10% deposit borrowing £207,000 would pay roughly £950 per month.

With median household income around £29,600 (£1,900 monthly after tax), that mortgage consumed 50% of take-home pay—high, but manageable for many.

By late 2023, the median house price had risen to £290,000, and rates had climbed to 5.5%.

A buyer with a 10% deposit borrowing £261,000 would pay approximately £1,615 per month.

With median household income at £32,300 (£2,050 monthly after tax), that mortgage consumed 79% of take-home pay—clearly unaffordable for most.

This comparison reveals the true affordability crisis: not that houses cost more relative to incomes (though they do), but that the monthly cost of servicing the debt required to buy them has risen far faster than incomes.

What this means for property investors

Buy-to-let investors must recalibrate their expectations in a higher-rate environment.

Properties that generated positive cash flow at 3% mortgage rates may now run at a loss at 5.5%, even if rents have increased.

The key metric for investors isn't gross yield but net yield after financing costs.

Calculate this by subtracting annual mortgage interest from annual rent, then dividing by the total property value.

A property worth £200,000 generating £12,000 annual rent with £8,250 in annual interest costs has a net yield of 1.875%—barely better than a savings account, and that's before maintenance, voids, and letting fees.

Many investors who purchased in the low-rate era are now trapped.

They can't sell without crystallising a loss (because property values have stagnated or fallen in many areas), but they can't refinance without accepting significantly higher rates that eliminate their cash flow.

This creates a hidden cohort of "zombie landlords" who are technically solvent but generating minimal or negative returns.

Looking ahead: what happens when rates fall

If and when mortgage rates decline—whether through Bank of England base rate cuts or increased competition among lenders—affordability will improve, but not symmetrically.

Borrowing capacity will increase, but so will buyer demand, potentially pushing prices higher and offsetting some of the benefit.

The buyers who benefit most from falling rates are those with existing mortgages coming off fixed terms.

Someone who fixed at 5.5% in 2023 and remortgages at 4% in 2025 will see their monthly payment drop by roughly £200 on a £250,000 mortgage—a meaningful saving that frees up cash for other expenses or overpayments.

First-time buyers will see some improvement in borrowing capacity, but they'll also face renewed competition from investors and second-steppers who were priced out during the high-rate period.

The net effect on house prices is difficult to predict, but history suggests that falling rates tend to support prices rather than reduce them.

Practical steps for buyers in a distorted market

Given these distortions, buyers need to focus on what they can control: their monthly budget, their deposit size, and their choice of property.

Here are concrete steps to improve your position:

First, maximise your deposit.

Every additional £5,000 you save not only reduces your mortgage but may unlock a better rate tier.

The jump from 90% LTV to 85% LTV typically saves 0.3-0.4 percentage points, which translates to roughly £50-70 monthly on a £200,000 mortgage.

Second, consider properties that need cosmetic work.

A house requiring new carpets and a fresh coat of paint will sell for less than a pristine equivalent, but the mortgage rate is the same.

If you can add £10,000 of value through DIY improvements, you've effectively bought at a discount—and you'll benefit from that equity when you remortgage or sell.

Third, look at areas with strong rental demand if you might need to let the property in future.

A house that's easy to rent provides flexibility if your circumstances change—you can move for work without being forced to sell in an unfavourable market.

Fourth, model your finances at higher rates.

If you're fixing for two years, assume you'll remortgage at 1-2 percentage points above the current rate.

If that scenario is unaffordable, you're borrowing too much.

Why this matters for policy and reporting

The persistence of price-to-earnings ratios in affordability discussions isn't just an academic problem—it shapes policy decisions and public understanding.

When politicians and journalists cite these ratios to argue that housing is "X times less affordable than in 1990," they're comparing apples to oranges.

In 1990, mortgage rates averaged 13-15%.

A house costing 3.5 times earnings required monthly payments that consumed a far larger share of income than a house costing 8 times earnings at 2% rates.

The price-to-earnings ratio was lower, but affordability—measured by monthly cost—was arguably worse.

Better metrics would focus on the monthly cost of servicing a mortgage as a percentage of median income, adjusted for typical deposit sizes and mortgage terms.

This would give a clearer picture of whether housing is becoming more or less accessible over time, and it would help buyers make more informed decisions about what they can genuinely afford.

Until we shift the conversation away from price multiples and toward payment affordability, we'll continue to misdiagnose the problem and propose solutions that don't address the real barriers facing buyers and investors in the UK property market.