How much mortgage can you afford? Debt-to-income explained
Before a bank approves your mortgage, it runs one critical calculation: your debt-to-income ratio (DTI). That single number sets how much you can borrow, and it usually weighs more than your credit score or your savings. Working it out before you apply tells you which asking prices are realistic.
- DTI = monthly debt payments / monthly income (gross in most countries, net in Spain); most European banks cap it at 35–40%
- All debts count, not just the mortgage: car loans, credit cards and personal loans
- Joint applications combine both incomes and both debts
- Paying down other debts before applying can significantly increase your maximum mortgage
- The bank's maximum is not what you should borrow: 28–30% leaves a comfortable margin
- Banks stress test at 2–3 points above the current rate, so a variable mortgage has to hold up if rates rise
What is the debt-to-income ratio?
DTI = (Total Monthly Debt Payments / Gross Monthly Income) × 100. If your gross monthly income is €4,000 and your total monthly debts (existing loans + proposed mortgage payment) are €1,200, your DTI = 30%. Most European banks use a 35–40% DTI limit as the maximum they'll approve, though 30% or below is considered healthy.
Front-end vs. back-end DTI
Front-end DTI counts only housing costs (mortgage principal + interest + property tax + insurance) as a percentage of income. Back-end DTI includes every debt: housing plus car loans, student loans and credit cards. Most banks focus on back-end DTI for mortgage qualification. In Spain, the Bank of Spain recommends that total mortgage debt not exceed 30–35% of net income.
How to increase your borrowing capacity
Four levers. Increase income: lenders work from gross pay, so a raise or documented side income counts. Pay down existing debt: every car payment or card balance you clear improves the ratio straight away. Put down a larger deposit: borrowing less means a smaller monthly payment. Stretch the term: going from 20 to 30 years lowers the payment, but you pay more interest overall.
Applying jointly: how two incomes change the calculation
When two people apply together, the bank adds both net incomes. With two salaries of €2,000 each (€4,000 combined), the 35% debt ceiling becomes €1,400/month across all debts. It is one of the most effective ways to raise borrowing capacity, but both applicants' debts are added up too. If one partner has a car loan or student debt, that reduces the shared ceiling just as much as the income raises it.
What banks don't tell you: approval maximum ≠ what you should borrow
Just because a bank approves you for €350,000 doesn't mean you should borrow €350,000. Bank limits are maximums, not recommendations. A DTI of 38% leaves little margin for emergencies, job loss, or rate rises on a variable mortgage. Financial advisers typically recommend keeping the mortgage payment at 28–30% of net income, leaving the remaining headroom to the 35% cap for other debts. The gap between what the bank permits and what is prudent can mean years of unnecessary financial pressure.
Frequently asked questions
What is the debt-to-income ratio?
The share of your gross (or net, in some countries) monthly income that goes to debt payments, including the new mortgage.
What DTI do lenders accept?
Many lenders prefer total debt payments below 35–43% of income. In Spain, banks usually cap the mortgage payment at around 30–35% of net income.
How can I increase my borrowing capacity?
Pay off consumer debt, increase your down payment, extend the term or apply jointly with a second income.
Should I borrow the maximum approved?
Not necessarily. Leave room for savings, rate rises and unexpected expenses.