Last reviewed: June 2026
TL;DR- Existing debts (credit cards, personal loans, car finance, student loans) are treated as committed expenditure in mortgage affordability assessments, reducing the maximum loan.
- UK lenders do not use a formal debt-to-income ratio metric as US lenders do, but the same concept applies through the affordability expenditure assessment.
- Paying off unsecured debt before applying for a mortgage is one of the most effective ways to increase the maximum mortgage available.
- Even a zero-balance credit card counts as a potential commitment - some lenders count a percentage of the credit limit as potential expenditure.
How UK Lenders Treat Existing Debt
UK mortgage lenders assess existing debt through the FCA-required affordability assessment. All regular debt repayments - personal loan payments, car finance payments, minimum credit card payments, student loan repayments and any other credit commitments - are deducted from disposable income as committed expenditure before assessing how much of the remaining income can service a new mortgage.
This is functionally equivalent to a debt-to-income (DTI) ratio assessment, though UK lenders do not typically present it in those terms. The effect is clear: the more existing debt commitments a borrower has, the less income is available to service a mortgage, and the lower the maximum mortgage the lender will offer.
Credit Card Treatment
Credit cards present a specific nuance in affordability assessments. Even where the balance is zero, lenders may treat a percentage of the available credit limit as a potential monthly commitment. The rationale is that the borrower could use the available credit at any time, creating a future commitment. Lenders typically count 2-5% of the credit limit per month as a notional commitment when there is no current balance. A borrower with £20,000 of unused credit card limits could have £400-£1,000 per month added to their assessed commitments, reducing the maximum mortgage significantly.
Closing unused credit cards before a mortgage application removes this notional commitment from the assessment and can meaningfully improve the maximum loan available.
Student Loan Repayments
Student loan repayments are deducted from assessable income in mortgage affordability assessments. The monthly repayment is calculated on the student's plan type and income level. For a graduate on Plan 2 earning £40,000, the monthly student loan repayment is approximately £65 per month. While this is not large, it contributes to the committed expenditure total. Student loan repayments cannot be waived or deferred for mortgage purposes - they are treated as a fixed commitment by lenders.
Reducing Debt to Improve Affordability
Paying off or reducing existing debts before a mortgage application is one of the most effective strategies for improving affordability. Priorities should be: clear outstanding personal loans (removing the monthly payment entirely); close unused credit cards (removing the notional commitment); reduce credit card balances where they carry a minimum payment; and consider whether overpaying car finance is possible. Each reduction in committed expenditure increases the disposable income available for mortgage servicing and can materially increase the maximum loan.
Frequently Asked Questions
Should I pay off debt or save a larger deposit before applying for a mortgage?
This depends on the relative impact on the maximum loan. Paying off a personal loan removes the monthly payment from committed expenditure, which may increase the maximum mortgage by a multiple of the loan balance. Saving a larger deposit reduces the LTV but increases the maximum loan only by the additional deposit amount. In general, paying off high-interest unsecured debt is beneficial both for the affordability assessment and for personal finances - but a broker or financial adviser can model the specific impact for a given debt and deposit situation.
Does my partner's debt affect a joint mortgage application?
Yes. In a joint mortgage application, both borrowers' debts are assessed as committed expenditure against the combined income. A partner with significant personal loan or credit card debt reduces the maximum joint mortgage even if the other partner has no debts. This is a common consideration when deciding whether to apply jointly or for one partner to apply alone.
How does car finance affect mortgage affordability?
Car finance (PCP, HP or personal loan for a vehicle) is treated as a committed monthly outgoing in the same way as any other debt. The monthly payment is deducted from assessable income. A £300 per month car finance payment reduces the income available for the mortgage stress test by £300 per month. Finishing car finance before a mortgage application or choosing a shorter car finance term that ends before the expected mortgage application date can improve affordability.
If I consolidate my debts into the mortgage, does that improve affordability on the new mortgage?
Debt consolidation into a mortgage reduces the monthly committed expenditure from the existing debts but increases the mortgage balance. The net effect on the new lender's affordability assessment depends on how the lender treats the new higher mortgage balance. The existing debts must be repaid at completion, so the consolidated debts do not appear as separate commitments on the new affordability assessment. However, borrowers should carefully consider the long-term cost of converting short-term unsecured debt into a long-term secured mortgage - the interest saved in the short term may be outweighed by interest paid over a longer mortgage term.
