How Much Can I Borrow? What the Lender Is Actually Calculating
Everyone asks the question as though there is one answer. There is not, because lenders apply three separate tests and the binding one changes from applicant to applicant.
Two people with identical salaries routinely get offers thousands apart, and the reason is almost never the salary. It is a car loan, a stress test, or the way the income is evidenced.
The three tests#
A lender applies all of these and offers the lowest result. Knowing which one is binding for you tells you what would actually change the answer.
- Income multiple. A cap on the loan as a multiple of gross annual income — commonly around four to four and a half times, with limited scope above.
- Debt-to-income. Total monthly debt payments as a share of gross monthly income, capped by regulation in several markets.
- Affordability assessment. A full budget: income minus committed spending, essential costs and dependants, tested against the payment.
- Loan to value. A separate cap based on the property, not on you — it limits the loan regardless of income.
If the multiple binds, you need more income. If DTI binds, clearing a loan helps enormously. If affordability binds, reducing regular outgoings helps. They are not interchangeable.
The stress test#
The payment that matters is not the one at the offered rate. Regulators in most markets require lenders to check that the borrower could still pay at a materially higher rate — commonly two to three percentage points above, or above a reversion rate. That is why a payment you can plainly afford can still be refused.
| Loan | Payment at 4.5% | Payment at 7.5% (stressed) | Difference |
|---|---|---|---|
| 150,000 | 834 | 1,109 | +33% |
| 250,000 | 1,389 | 1,848 | +33% |
| 350,000 | 1,945 | 2,587 | +33% |
| 500,000 | 2,779 | 3,696 | +33% |
Illustrative, 25-year term. The stress uplift is roughly a third at these levels, and it is applied to the payment you must be shown to afford — not the one you will pay.
What counts as income, and what does not#
| Income type | Typically counted | Notes |
|---|---|---|
| Basic salary | In full | The straightforward case |
| Regular overtime | Partly, often 50% | Needs a history |
| Bonus | Partly, averaged | Two to three years of evidence usually required |
| Self-employed profit | Yes | Two to three years of accounts; averaged, or the lower year |
| Rental income | Partly | Often discounted for voids and costs |
| Benefits and allowances | Varies widely | Highly lender-specific |
| Second job | Often, with history | Needs to look durable |
This is where two identical salaries diverge. A salary of the same size delivered as basic pay and as basic-plus-bonus produces materially different offers.
What reduces the figure#
- Existing debt payments — a car loan is the classic case, and clearing one can add many times its balance to the borrowing figure.
- Credit card limits, which some lenders count as potential debt even at a zero balance.
- Dependants, which increase the assumed essential spending.
- Committed regular spending visible on statements — subscriptions, childcare, maintenance payments.
- A short remaining working life, where the term would run past retirement age.
- Irregular income, which is discounted before it is counted.
The car loan point is worth restating because it is so consistently underestimated: a monthly payment of a couple of hundred can reduce borrowing capacity by tens of thousands.
How to improve the answer#
- Clear or reduce short-term debt several months before applying, not the week before.
- Reduce credit card limits you do not use.
- Keep three to six months of clean statements: this period is what an underwriter reads.
- Increase the deposit if you can, which lowers the LTV band as well as the loan.
- Avoid changing job in the run-up, or apply after passing probation.
- Have the evidence assembled — payslips, accounts, tax computations — before applying, not after being asked.
None of this changes what you can genuinely afford. It changes whether the lender can see it, which is a different problem with a shorter timeline.
Frequently asked questions
How much can I borrow for a mortgage?
Lenders apply several tests and offer the lowest result: an income multiple, usually around four to four and a half times gross annual income; a debt-to-income cap, which is set by regulation in several markets; a full affordability assessment of your actual income minus committed spending; and a loan-to-value cap based on the property. Which one binds varies by applicant, and knowing which one it is tells you what would actually change the number.
Why is my mortgage offer lower than the online calculator said?
Usually one of three things. Existing debt — a car loan or a credit card limit — has reduced the affordability figure, often by much more than people expect. Part of your income has been discounted: bonus, overtime, self-employed profit and rental income are all counted partially or averaged. Or the stress test has bitten, because the lender must check that you could pay at a rate two or three points above the one offered, not at the one offered.
Does paying off a car loan increase how much I can borrow?
Often dramatically. Affordability is calculated from income minus committed payments, so removing a monthly obligation frees that amount for mortgage payments — and because the mortgage payment is capitalised over twenty-five or thirty years, a payment of a couple of hundred a month can be worth tens of thousands of borrowing capacity. Clear it several months before applying so the statements the underwriter reads are already clean.
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