Why Different Lenders Offer Different Mortgage Amounts

Income multiples: the biggest variable

The income multiple is the factor a lender applies to your gross annual salary to calculate a starting maximum mortgage amount. Across UK lenders, this multiple ranges from around 4x to 5.5x, and occasionally higher for specific professions or circumstances.

To see what this means in practice, consider a borrower earning £50,000 per year:

• At 4x income: maximum mortgage of £200,000
• At 4.5x income: maximum mortgage of £225,000
• At 5x income: maximum mortgage of £250,000
• At 5.5x income: maximum mortgage of £275,000

That is a £75,000 range from the same salary, before any other factors are considered. For a joint application on £80,000 combined income, the range would be £320,000 to £440,000.

Some lenders also adjust their income multiple based on other factors. For example, NatWest uses a tiered system where borrowers with larger deposits or higher incomes may qualify for a 5.5x multiple, while others receive 4.49x. Several lenders offer enhanced multiples to professionals such as doctors, accountants, and solicitors, reflecting lower perceived risk.

The FPC's loan-to-income (LTI) flow limit restricts lenders from issuing more than 15% of their new mortgage lending at 4.5x income or above. This means lenders that offer high multiples cannot do so for every borrower, and they tend to reserve higher multiples for applicants who meet specific criteria.

Stress test rates and why they matter

While income multiples provide the initial estimate, the stress test is where affordability calculations really diverge between lenders. Every UK lender applies a stressed interest rate to check whether you could still afford your monthly payments if rates were to rise.

Stress rates across the market typically range from about 6% to 8.5%. The difference might not sound large, but the impact on your maximum borrowing is significant.

Consider a 25-year repayment mortgage of £250,000:

• At a 6% stress rate: monthly payment of approximately £1,611
• At a 7% stress rate: monthly payment of approximately £1,767
• At an 8% stress rate: monthly payment of approximately £1,929

The lender using the 8% stress rate requires you to demonstrate you can afford £318 more per month than the lender using 6%. Working backwards, this means the 6% stress rate lender may offer you substantially more than the 8% lender, even if their headline income multiples are similar.

Since the Bank of England removed the FPC affordability stress test in August 2022, lenders have had more freedom to set their own stress rates. This has increased the variation between lenders rather than reduced it.

How lenders treat bonus, overtime, and commission

If you earn a straightforward salary with no additional income, the variation between lenders is largely driven by income multiples and stress rates. But if any portion of your income comes from bonus, overtime, or commission, the differences widen considerably.

Overtime income: Some lenders accept 100% of regular overtime if you have at least 12 months of history. Others cap it at 50%, and a few will only consider overtime if it has been consistent for two full years. If you earn £5,000 per year in overtime, the lender that accepts 100% adds £5,000 to your assessable income, while the one accepting 50% adds only £2,500. At a 4.5x multiple, that is a difference of £11,250.

Bonus income: The variation here is even greater. Common approaches include taking the average of the last two years, using the lower of the last two years, averaging three years, or accepting the most recent year's figure. Some lenders cap bonus acceptance at a percentage of basic salary (for example, no more than 50% or 75% of base). A borrower with a £15,000 average bonus could see their assessable income differ by £7,500 or more between lenders.

Commission income: Lenders that cater to sales professionals tend to be significantly more generous with commission. Some accept up to 100% of a two-year average, while others treat commission the same as bonus income and apply the same restrictions.

For borrowers with significant variable income, the gap between the most and least generous lender can exceed £50,000 in maximum borrowing. This is one of the strongest arguments for checking multiple lenders rather than relying on a single calculation.

Self-employed income: the widest variation

Self-employed income is where lender differences are at their most extreme. The core question is the same -- how much of your income will the lender count? -- but the methods for answering it vary dramatically.

Sole traders: Most lenders use the average of your last two years' net profit from your SA302 tax calculations. Some use the average of three years. A few use the most recent year if it is lower (a conservative approach) or the most recent year if it is higher (a generous approach). If your profits have been growing, the difference between a lender using a two-year average and one using only the most recent year can be substantial.

Limited company directors: The traditional approach was to assess salary plus dividends. Many lenders now accept salary plus net profit (or salary plus the director's share of net profit), which is often more favourable for directors who retain profits in the company. The difference between these two methods can be tens of thousands of pounds in assessable income.

Contractors: Some specialist lenders assess contractors based on their day rate multiplied by a notional number of working weeks (typically 46 or 48), rather than requiring traditional accounts. This can produce significantly higher assessable income than the standard approach.

We cover this topic in much more detail in our dedicated self-employed mortgage affordability guide.

Outgoings and expenditure floors

Affordability is not just about income -- your outgoings play a significant role too, and lenders assess them differently.

Credit commitments: All lenders deduct existing credit commitments from your disposable income. However, the treatment of credit card balances varies. Some lenders use your actual monthly payment, some apply a percentage of your outstanding balance (typically 3% to 5%), and others apply a percentage of your total credit limit regardless of what you owe. A borrower with a £10,000 credit limit but zero balance might have £0, £300, or £500 deducted from their monthly disposable income depending on the lender.

Expenditure floors: Many lenders apply minimum living cost assumptions regardless of what you declare. These are based on household size and are derived from ONS data or the lender's own research. A single applicant might face a minimum living cost assumption of £600 to £900 per month, while a family of four might face £1,200 to £1,800. The exact figures vary considerably between lenders.

Student loans: Student loan repayments are calculated based on income thresholds. Plan 2 borrowers repay 9% of income above £27,295. Most lenders model this consistently, but some allow borrowers who are close to paying off their loan to have it excluded from affordability calculations.

Banks vs building societies

There is a common perception that building societies are more generous or flexible than high-street banks. Like most generalisations about mortgage lending, this is partially true but not universally so.

Building societies are mutual organisations owned by their members. They are not subject to shareholder pressure to the same degree as publicly listed banks, and some do take a more individual approach to affordability assessment. Several building societies are known for:

• Accepting a higher percentage of overtime and bonus income
• Being more accommodating with self-employed income, including accepting one year of accounts in some cases
• Offering manual underwriting for cases that do not fit standard automated criteria
• Being more flexible on property types (older properties, non-standard construction)

However, building societies are also subject to the same FCA regulatory requirements as banks. They still apply stress tests, assess affordability in detail, and are bound by responsible lending rules. Some building societies are actually more conservative than the major banks in certain areas.

The takeaway is that you should not assume any single type of lender will be best for your situation. The right lender depends on your specific income profile, deposit size, and circumstances.

Real-world examples of the difference

To illustrate how much variation exists, consider these examples based on typical lender criteria in early 2026:

Example 1: Employed with overtime. A nurse earning £35,000 basic salary plus £8,000 per year in regular overtime. A lender accepting 100% of overtime at a 4.75x multiple would offer up to £204,250 (£43,000 x 4.75). A lender accepting only 50% of overtime at a 4x multiple would offer £156,000 (£39,000 x 4). Difference: £48,250.

Example 2: Joint applicants with bonus. A couple earning £45,000 and £38,000 basic, with one receiving a £12,000 annual bonus. A generous lender using 100% of the bonus at 5x would offer £475,000. A conservative lender using 50% of the bonus at 4.25x would offer £378,250. Difference: £96,750.

Example 3: Self-employed sole trader. A plumber with net profits of £42,000 (year 1) and £55,000 (year 2). A lender using the two-year average (£48,500) at 4.5x would offer £218,250. A lender using the latest year (£55,000) at 5x would offer £275,000. Difference: £56,750.

These are not extreme or unusual scenarios. They represent the kind of variation that borrowers encounter routinely when they check more than one lender.

Why checking multiple lenders matters

Given the variation described throughout this guide, it should be clear that relying on a single affordability check -- or using a generic online calculator that applies a flat 4.5x multiple -- can give you a misleading picture of what you can actually borrow.

Checking multiple lenders is particularly important if:

• You receive bonus, overtime, or commission income that makes up a meaningful portion of your total earnings
• You are self-employed and want to find the lender that treats your accounts most favourably
• You have existing credit commitments and want to understand how different lenders treat them
• You are stretching your budget and need to know the maximum you could borrow across the market
• You are a joint applicant where one partner has variable income

Mortgage Affordability lets you check your borrowing across 60 UK lenders at once. You enter your details once, and we connect to each lender's actual affordability calculator -- not a generic estimate -- to show you the full range of what different lenders would offer.