Debt to Income Ratio Calculator
Calculate your debt-to-income ratio to assess loan affordability.
What this calculator does
This debt-to-income calculator shows what proportion of your gross monthly income goes to housing and to total debt commitments. Enter your gross monthly income, your monthly housing cost, and all your monthly debt payments, and it returns a front-end ratio for housing alone, a back-end ratio covering everything, and the headroom you have before hitting conventional limits.
In the UK these ratios sit alongside rather than instead of the tests lenders actually apply — loan-to-income multiples and a stressed affordability assessment. What the ratios give you is a fast, honest read on how loaded your income already is, which is the same thing the lender's more elaborate model is trying to establish.
When to use it
Use it several months before a mortgage application, because the commitments it measures take time to remove. UK lenders scrutinise three to six months of bank statements, so clearing a car finance agreement or an overdraft well ahead of applying shows up in the assessment where a last-minute payment does not.
It is also the tool for testing what a new commitment costs you in borrowing power. Taking a £300 PCP on a £4,200 monthly income consumes over seven percentage points of your ratio and cuts meaningfully into what a lender will advance. And it is worth running before a remortgage, since affordability is reassessed if you are moving lender or borrowing more.
Understanding the inputs
Gross monthly income is your pay before tax and National Insurance, including regular overtime, bonus, and commission that a lender would recognise, usually averaged over two years, plus any documented rental income.
Monthly housing cost is your mortgage or rent plus ground rent and service charge if you hold a leasehold property. Total monthly debt adds that housing figure to every other commitment: credit card minimums, personal loans, car finance, overdraft servicing, buy-now-pay-later instalments, and child maintenance. Student loan repayments are usually treated as an income deduction instead — if you want to reflect that, reduce the income figure by 9 percent of earnings above your plan threshold.
How is this calculated?
DTI Ratio = (Monthly Debt Payments / Monthly Gross Income) × 100
A worked example
Take £4,200 gross monthly income — around £50,400 a year — with £1,150 of housing cost. That is a front-end ratio of 27.4 percent, comfortably placed. Add £310 of car finance, £180 in credit card minimums, and £80 on a personal loan, giving £1,720 of total commitments and a back-end ratio of 41 percent.
That is above the conventional 36 percent guideline. It also matters for the mortgage itself: at 4.5 times income, £50,400 supports around £226,800 of borrowing before affordability reductions, and £570 a month of non-housing debt will pull the lender's actual offer materially below that ceiling.
Limitations and assumptions
These ratios are a useful proxy, not the test a UK lender runs. Lenders apply a loan-to-income cap, a detailed affordability model built on income, committed expenditure, dependants, and household costs, and a stress test at a rate well above the one you are being offered. A comfortable ratio here can still fail that model.
The calculator also uses gross income, so it ignores tax, National Insurance, pension contributions, and student loan deductions, which together can take a third or more of pay before anything is spent. Treat it as a starting diagnostic, then get a decision in principle for a figure that means something.
Common Questions
- Do UK mortgage lenders use debt-to-income?
- They use it as one input, but the binding constraint is usually loan-to-income. Since 2014 the Bank of England has limited the proportion of new mortgages lenders may write above 4.5 times income, so most UK borrowers hit an LTI ceiling before a DTI one. Existing debts reduce affordability within that framework rather than replacing it.
- What is the loan-to-income cap and how does it work?
- Lenders may write only a limited share of new mortgages at more than 4.5 times a borrower's income. In practice that means a household earning £50,000 will struggle to borrow much beyond £225,000 regardless of how comfortable the monthly figure looks. Your existing debts then reduce the amount further through the affordability assessment.
- What is an affordability stress test?
- Lenders must check you could still afford the mortgage if rates rose. Historically this meant testing at the reversion rate plus three percentage points, and although the FCA relaxed the specific rule in 2022, lenders still stress-test at rates well above the deal rate. That test, not the current payment, often determines the maximum.
- Which debts count against affordability?
- Credit card and store card minimum payments, personal loans, car finance including PCP and hire purchase, overdraft usage, buy-now-pay-later balances, and any child maintenance. Student loan repayments are treated as a deduction from income by most lenders rather than as a debt, because they come out through payroll.
- How do student loan repayments affect a mortgage application?
- They reduce your net income rather than counting as a debt, so their effect is real but indirect. A Plan 2 borrower repays 9 percent of income above the threshold, which on a £45,000 salary is roughly £100 a month leaving your pay before the lender assesses affordability. The outstanding balance itself is generally disregarded.
- Does a large overdraft hurt my application?
- Yes, more than many borrowers expect. Persistent overdraft use signals that spending exceeds income, and lenders read bank statements closely in the months before completion. Clearing an overdraft and staying out of it for three to six months before applying is one of the more effective preparations you can make.
- How do I improve affordability quickly?
- Clear a debt outright rather than reducing several. Affordability counts the monthly commitment, so ending a £280 car finance agreement helps far more than paying £3,000 off a credit card while keeping the account active. Reducing unused credit card limits can also help with some lenders, who assess potential rather than actual borrowing.
- Does this ratio affect my credit score?
- No. Experian, Equifax, and TransUnion do not hold your income, so their scores cannot reflect debt-to-income. Affordability is assessed separately by the lender during underwriting using your payslips and bank statements. A strong credit file and a failed affordability assessment frequently go together.
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