When people ask me how much they can borrow, they usually expect the answer to be about their salary. Income matters, of course, but one of the first things a lender actually looks at is how much of that income is already spoken for. That is your debt to income ratio, and in my experience it is the reason a lot of mortgage applications come back lower than people hoped.
This guide explains what debt to income ratio mortgage lenders in the UK look for, how to work out your own, what counts and what does not, and what you can do to improve it before you apply. I have kept it to how things actually work here, because a lot of what you read online is written for the American market and does not apply to a UK mortgage.
Your debt to income (DTI) ratio is the share of your gross monthly income that goes on monthly debt payments. Gross income means your income before tax and National Insurance.
It gives a lender a quick picture of your financial health and how stretched you are. Two people on the same salary can look very different on paper. One has no car finance and clears their credit card every month. The other has a car on finance, a personal loan and a couple of credit cards at their limit. The first has far more room for a mortgage, even though they earn exactly the same.
You can calculate your DTI ratio in a few minutes with your bank statements in front of you.
So the formula is: DTI = (total monthly debt payments ÷ gross monthly income) × 100.
Say you earn £42,000 a year. That is £3,500 a month before tax. Each month you pay:
That is £445 a month, so your DTI ratio is £445 ÷ £3,500 × 100, which comes to about 13%. That would look healthy to most lenders.
Now add the mortgage you want. If the new mortgage payment would be £1,100 a month, your total monthly debts become £1,545, and your DTI ratio with the mortgage is about 44%. Your housing costs are usually the biggest single part of the total. Lenders look at both numbers: what you owe now, and what things look like once the mortgage is in place.
Lenders will see most of your credit commitments on your credit report, and the rest on your bank statements. These are the ones that usually count:
A loan with only a few months left can sometimes be ignored, but that is down to the individual lender, so it is worth asking before you assume.
Your DTI ratio only looks at debt payments. These costs are not part of the ratio:
That does not mean lenders ignore them. They come into the wider mortgage affordability check, which looks at your monthly bills, childcare and household costs as well as your debts. Your DTI ratio is one part of that picture rather than the whole of it.
Lenders start with your basic salary, but most will look at more than that, depending on their criteria:
How much of this a lender will use varies a lot, which is one of the main reasons the same person can be offered very different amounts by different lenders.
There is no single number that every UK lender works to. Each one has its own lending criteria, and your DTI ratio sits alongside your credit history, deposit and the affordability calculation. As a rough guide from the cases I see:
These are the figures before the new mortgage is added. Once the mortgage payment is included, most lenders expect the total to be higher, and that is normal.
This is where UK lending differs from what you might read elsewhere. Most UK lenders set a cap based on income multiples, typically up to 4.5 times your income, with some going to 5 or 5.5 times, and a few up to 6 times for certain professions or higher earners.
Your debts then pull that figure down. On £42,000, a 4.5 times multiple would suggest £189,000. But the lender's affordability model takes your monthly debt payments into account, so the £445 a month in the example above could reduce the maximum loan by tens of thousands of pounds. That is why clearing a car finance agreement or a credit card can make a bigger difference to your borrowing than a pay rise. Our mortgage borrowing calculator will give you a starting figure.
Since 2014, each lender could only write 15% of its new residential mortgages at 4.5 times income or more. From 28 October 2026, the Bank of England and the FCA have replaced that with a single 15% limit across the whole market, so individual lenders can go above it as long as the total across all lenders stays within the limit.
In practice, this should mean more lenders willing to offer higher income multiples, which helps first time buyers in particular. It does not change the affordability checks, though. Your DTI ratio will matter just as much, because lenders still have to be confident you can afford the payments.
No. Credit files in the UK do not record your income, so your DTI ratio is not part of your credit score. Lenders work it out themselves from your application, payslips and bank statements.
Often, yes, but you will have fewer lenders to choose from and you may not be able to borrow as much. A bigger deposit, a strong credit history and the right lender can all make up for a high DTI ratio and a larger total debt.
When you are buying a home, your rent usually stops once you move in, so lenders do not normally count it. It is different if you are keeping a rented property on, or if you pay rent somewhere else.
Yes. Lenders add up both incomes and both sets of debts, so one person's car finance or credit card payments affect the joint DTI ratio.
If you would like me or one of the team to look at your numbers before you apply, book a free call. Most of the time we can tell you which lenders will be most comfortable with your debts, and whether clearing one of them first would make a real difference to what you can borrow.
Your home may be repossessed if you do not keep up repayments on your mortgage.
