What is Debt-to-Income (DTI) ratio?
Debt-to-Income ratio expresses your total monthly debt repayments as a percentage of your net (take-home) monthly income. It's one of the clearest, most widely referenced metrics UK lenders use to judge affordability — a straightforward way to assess how much of your income is already committed before any new borrowing is even considered.
The formula behind this calculator
This calculator adds together your rent or mortgage payment, loan repayments, credit card minimum payments and any other regular credit commitments, then expresses that total as a percentage of your net monthly income — exactly mirroring the core calculation lenders perform as part of a fuller affordability assessment.
Why lenders rely on DTI so heavily
DTI gives lenders a quick, standardised way to gauge how much financial "room" you realistically have for a new commitment, independent of the absolute size of your income. Someone earning a high salary but with very high existing debt repayments may have less genuine capacity for new borrowing than someone earning less with minimal existing commitments — DTI captures this relative picture in a single, comparable number.
How to interpret your DTI result
| DTI range | General interpretation |
|---|---|
| Below 20% | Generally viewed favourably — meaningful capacity for new borrowing |
| 20% – 36% | Manageable — comfortable for many mainstream lenders |
| 36% – 43% | Getting stretched — some lenders may reduce the amount offered |
| Above 43% | High — likely to significantly restrict borrowing options |
These bands are general guidance, not a universal rule — actual lending thresholds vary significantly by lender, loan type and individual circumstances, and some specialist lenders serve borrowers with higher DTI ratios than mainstream criteria would typically accept.
DTI for mortgages vs DTI for personal loans
While the underlying DTI concept applies across both mortgage and personal loan lending, mortgage affordability assessments are typically considerably more detailed — incorporating the formal stress test explained in our mortgage affordability guide, alongside bank statement analysis and dependant adjustments that go well beyond a simple DTI calculation. Personal loan and credit card affordability checks tend to reference DTI-style calculations somewhat more directly, though still alongside other factors like credit history.
Practical steps to improve your DTI before applying
- Pay down high-interest debt first — clearing a credit card or short-term loan directly reduces your monthly debt figure and therefore your DTI
- Avoid taking on new credit commitments shortly before a major application, even seemingly small ones
- Consider whether increasing net income is realistic — a pay rise, side income, or claiming an entitled benefit or tax relief can improve the ratio from the income side rather than only the debt side
- Time larger applications carefully — if you know a debt (such as a car finance agreement or short-term loan) is due to be cleared soon, it may be worth waiting until afterward if timing allows, since your DTI will naturally improve
You may also find our guide on How UK Lenders Calculate Affordability and DTI useful.
The bottom line
Your Debt-to-Income ratio is one of the most direct, lender-relevant metrics you can check yourself before applying for a mortgage or loan. Use this calculator to see roughly where you stand, and treat a high result not as a dead end but as a clear, actionable signal of where to focus — usually paying down existing debt — before your next application.