A buyer earning £55,000 with a reasonable deposit asks two mortgage lenders how much they might lend. One calculation produces roughly the amount needed for the property. The other comes back £40,000 short. Same income, same deposit, same debts, same property — but a materially different answer.
Nothing about this necessarily means one lender has made a mistake. It is simply how mortgage lending works, and it catches out borrowers who assume, reasonably enough, that “the bank” applies more or less the same maths as every other bank.
It doesn’t. Mortgage lending operates within a shared regulatory framework, but that framework does not prescribe one national affordability calculator. Above the minimum requirements, lenders retain considerable freedom over what they are prepared to lend, which income they recognise, which risks they will accept and even which properties they are prepared to take as security.
The detailed FCA affordability rules discussed below principally concern regulated residential mortgages. Most conventional buy-to-let mortgages do not sit within the same FCA regulatory framework, while consumer buy-to-let has a separate regime. For landlords and investors, the precise rules are therefore different — although the broader point that lenders apply their own affordability, risk and property criteria still holds. FCA — Products and services we do and don’t regulate
That distinction matters because a mortgage decision is not one test. It is several overlapping decisions — about affordability, credit risk, the lender’s own appetite and the property itself — and different lenders can reach different conclusions at almost every stage.
The regulatory floor: what every lender must do
The Financial Conduct Authority’s mortgage rules require lenders to make a proper assessment of whether a borrower can afford the mortgage, rather than relying simply on the applicant’s view that the monthly payment looks manageable. Income must be evidenced appropriately, committed expenditure has to be taken into account and the lender must consider the borrower’s ability to meet the payments.
For mortgages caught by the FCA’s interest-rate stress rule, MCOB 11.6.18R also requires the lender to consider likely interest rates over at least the first five years. Mortgages fixed for five years or longer are generally outside that particular requirement. Where the rule does apply, even if market expectations suggest rates will fall or rise by less than one percentage point, the lender must assume a minimum rise of one percentage point. What the FCA does not impose is a single common stress rate that every lender must use. FCA — Interest rate stress test rule
That distinction has become increasingly important. The FCA has explicitly reminded lenders that they already have flexibility within the existing rule and, after reviewing it, concluded that no further policy change to the interest-rate stress test itself was currently required.
There is another regulatory constraint operating at market level: high loan-to-income lending. Historically, larger lenders were generally restricted so that no more than 15% of their new residential mortgages could be at an income multiple above 4.5. That framework is now in transition.
Following a Financial Policy Committee recommendation in 2025, the direction of policy has shifted towards keeping high-LTI lending consistent with roughly 15% of new mortgage lending across the market as a whole, while allowing individual lenders more freedom over how much high-LTI business they write. Since July 2025, firms within scope have been able to opt into a PRA modification that removes their individual 15% flow limit, subject to additional risk-management and reporting requirements. The current modification runs until 31 December 2026, or until the underlying rule is changed earlier. Bank of England — Housing LTI flow-limit modification
That is not an obscure regulatory distinction. It means two lenders can legitimately have very different appetites for lending at higher income multiples. One may actively use the additional capacity because it wants more first-time-buyer or professional business; another may remain well below the limit because its own risk appetite, funding model or target market points elsewhere.
By September 2026, high-LTI mortgages accounted for 14.1% of lending in the latest quarter, with the four-quarter average at 12.0%. Among first-time buyers, the latest quarterly share had reached 18.1%. The market is therefore using considerably more of the permitted high-LTI capacity than it was previously. Bank of England — Financial Policy Committee Record, September 2026
Put together, this is the regulatory floor and market-wide safety framework. It requires responsible affordability assessment and limits excessive high-income-multiple lending in aggregate. It deliberately does not require every lender to reach the same answer on the same borrower.
The lender-specific ceiling: where the real variation lives
Above that regulatory floor, each lender builds its own lending policy around its cost of funding, risk appetite, target customers, product strategy and view of different types of income and security. This is where much of the variation borrowers actually experience appears.
Income and employment. A straightforward permanent salary is usually the least contentious part of an affordability assessment. Once income becomes less predictable, lender policies can diverge quickly. Bonus, commission and overtime may be averaged, discounted or accepted differently depending on the lender and the applicant’s history. Self-employed profit, company-director income, contract work and multiple sources of earnings can also be treated in materially different ways.
That means two lenders can look at the same total annual earnings and start their affordability calculations from different assessable-income figures before either has considered anything else.
Committed expenditure and dependants. Existing borrowing matters too, but lenders do not necessarily model it identically. Car finance, loans, credit cards, student-loan deductions, childcare and other committed expenditure all reduce the amount available to service a mortgage. One lender may also take a different view from another where a credit commitment is shortly due to end, or use different assumptions about the living costs associated with children and other dependants.
The result is that two households with identical gross incomes can have very different borrowing capacities — but also that two lenders can produce different answers for the same household.
Credit history is not one universal score. Borrowers are often understandably focused on the consumer credit score they see from a credit-reference agency. But there is no single UK mortgage score that every lender consults and either accepts or rejects.
Lenders can use information from credit-reference agencies alongside the mortgage application, information they already hold about an existing customer and their own internal scoring and lending policy. A strong consumer-facing credit score is useful evidence of a healthy credit history, but it is not a pass mark that obliges every mortgage lender to approve the application. Experian — Credit scores and mortgages
That helps explain why a historic missed payment, default or other adverse event can produce very different outcomes. One lender may have a hard policy restriction; another may accept the event once it is old enough or small enough; a specialist lender may deliberately operate in that part of the market and price the additional risk accordingly.
Age and mortgage term. Maximum lending age, acceptable retirement income and the treatment of a mortgage that runs beyond expected retirement can differ between lenders. A longer term can make the monthly payment more affordable and increase the amount available to borrow, but the applicant still has to meet that lender’s criteria for income later in the term.
This is one reason an older borrower can receive substantially different maximum loan amounts even where the lenders are looking at the same present-day salary.
Loan-to-value and lender appetite. Deposit size affects risk, but the relationship is not simply “bigger deposit equals automatic acceptance”. Lenders decide how much business they want at different loan-to-value bands, just as they decide how much higher-LTI lending they want. Pricing, funding conditions and portfolio strategy can change those appetites over time.
A lender trying to expand in a particular segment may therefore be materially more competitive for one type of borrower than another institution whose balance sheet is already heavily exposed to that part of the market.
The property is a separate lending decision. This is one of the easiest parts of mortgage underwriting to overlook. Passing the affordability assessment does not necessarily mean the lender will accept the home being purchased as adequate security for the loan.
Flats above commercial premises, some ex-local-authority properties, unusual construction methods, short leases and other properties outside a lender’s preferred security criteria can be acceptable to one lender and unacceptable to another. The exact issue and policy vary, but the principle is important: a borrower can be mortgageable while a particular property is not mortgageable to that particular lender.
That distinction matters to sellers, estate agents and investors as much as to the person applying for the loan. It also explains why an Agreement in Principle, Decision in Principle or Mortgage in Principle should not be mistaken for final approval of a purchase. It gives an indication of how much a lender might be willing to lend based on the information considered at that stage; it is not a guarantee of the final mortgage offer. The lender can still reduce the loan or refuse to proceed after the full application and valuation if the property does not meet its requirements. MoneyHelper — The mortgage application process
For an estate agent assessing competing buyers, that is an important distinction. An agreement in principle says something useful about the buyer’s likely borrowing capacity, but it does not prove that the lender will finance the particular flat or house the buyer eventually chooses.
Automated decisioning versus manual underwriting
Many mortgage decisions are heavily automated. Applicant information is run through affordability, credit and policy rules, allowing straightforward cases to move quickly and cases outside the lender’s parameters to be declined or referred for further assessment.
A referral to manual underwriting changes the way the evidence can be considered, but it does not make the lender’s rules disappear.
A human underwriter may be able to assess context that an automated process cannot handle neatly: irregular income supported by a clear history, an explainable credit event, additional evidence of affordability or a property requiring closer consideration. But the underwriter still operates within the lender’s policy. If that policy says a particular construction type, credit event or income source is unacceptable, manual review is not a general power to ignore the restriction because the rest of the application looks sensible.
That distinction also explains the more useful role of a mortgage broker in a complex case. The value is not simply finding an underwriter who is “more flexible”. It is understanding before an application is made which lender’s criteria are more likely to fit the applicant’s income, credit history, required borrowing and property — and which lenders are unlikely to fit regardless of how persuasively the case is presented.
That can matter where the differences between lenders are substantial. An unnecessary application to a lender whose policy could never accommodate the case costs time and may complicate an already time-sensitive purchase.
The regulatory direction is likely to make some of these differences more, rather than less, visible. The FCA’s wider Mortgage Rule Review is considering targeted changes for borrowers with variable income, past credit difficulties and other circumstances that can sit awkwardly with conventional underwriting. Its 2026 responsible-lending consultation closed in July and, as at October 2026, the proposed changes should still be treated as proposals rather than settled rules. FCA — Mortgage Rule Review: responsible lending consultation
The same applies to rental-payment history. The FCA has considered whether an established record of paying rent can play a larger role in mortgage decisions, but it has not replaced affordability assessment with a simple “if you can pay the rent, you can afford the mortgage” rule. The regulator identified limitations in rent alone — including changes in interest rates, homeownership costs and the fact that rent may itself have been met using credit — and is instead supporting further industry use and development of rental-payment data within wider affordability assessment. FCA — Mortgage Rule Review feedback and roadmap
A simplified illustration
Consider a hypothetical borrower earning a £40,000 basic salary plus an annual bonus that has averaged £15,000 during the past three years but has moved noticeably from year to year.
Lender A might decide that the uncertain nature of the bonus means it will use only half of the three-year average for its affordability assessment, giving the borrower £47,500 of assessable income before the rest of the calculation is applied.
Lender B might use a different policy — perhaps placing more weight on the most recent bonus once the applicant has demonstrated the track record that lender requires. If the borrower’s bonus is increasing, that could make Lender B considerably more generous. If the latest bonus has fallen sharply, the opposite could be true.
The example is deliberately simplified and does not represent the policy of any named lender. Actual criteria are considerably more detailed and can change. The point is that both lenders can look at exactly the same evidence, apply legitimate but different policies to uncertain income and reach different maximum loan figures without either having calculated affordability “wrong”.
And income may not be the reason for the difference at all. If one lender is comfortable with the required income multiple and the other is restricting high-LTI lending, or one accepts the property while the other does not, the divergence may arise elsewhere in the decision.
What this means in practice
A decline from one lender is information about that lender’s criteria applied to that case at that time. It is not automatically a verdict that no mortgage is available.
But the opposite conclusion is equally important: the existence of lender variation is not a reason simply to keep making applications until somebody says yes.
The useful question is why the first answer was no — or why the maximum loan was lower than expected.
If the problem is how bonus or self-employed income has been assessed, another lender’s income policy may produce a different result. If it is a hard credit rule, the options will depend on the event and the lenders prepared to accept it. If the problem is the requested income multiple, another lender may have more appetite for higher-LTI business. If the difficulty is the property itself, changing lender may help only if the next lender is genuinely comfortable with that security.
And if the underlying issue is that the mortgage simply does not look affordable even after reasonable lender variation is considered, shopping around does not make that affordability problem disappear.
That is why headline borrowing multiples and online affordability calculators can only go so far. Property Front Page examines the wider affordability question in How Much Mortgage Can You Really Afford?. The more useful starting point here is to identify which part of the lending decision is actually constraining the case.
Mortgage lenders operate under common rules, but they are not interchangeable versions of the same institution. They compete for different customers, price different risks, recognise income differently, set different portfolio limits and take different views of property security.
The surprise is therefore not that two lenders sometimes produce different answers. Given how many separate judgements sit behind a mortgage decision, it would be more surprising if they always produced the same one.
This article provides general information about regulated UK residential mortgage lending and is not mortgage or financial advice. Lending criteria and affordability assessments vary between lenders and can change over time. Most conventional buy-to-let mortgages operate under a different regulatory framework. Anyone considering a mortgage should base decisions on their own circumstances and, where appropriate, seek regulated mortgage advice.
