Working out how much you can borrow is an essential first step when buying your first home in the UK. This guide shows you how to make a sensible borrowing estimate, build a monthly-payment worksheet, account for debts and buying costs, and identify when your figures need to be reviewed.
Overview
A lender’s maximum offer is not the same as a comfortable budget. Your borrowing may be influenced by household income, regular spending, existing credit commitments, deposit size, credit history, employment circumstances and the mortgage product available when you apply.
Most lenders also assess whether you could continue to pay the mortgage if circumstances became more difficult, such as a rise in the interest rate, a drop in variable income or an increase in household costs. The result is a tailored affordability assessment rather than a simple salary multiplier.
Use an online UK mortgage calculator for an initial estimate, but treat the result as a planning tool. A calculator may not include every lender’s rules, your full spending profile or the costs of buying a house. An agreement in principle can provide a more specific indication, although it is not a guarantee that a mortgage will be approved.
Before viewing properties seriously, set two figures:
- Estimated maximum borrowing: a broad indication of the loan a lender might consider.
- Comfortable borrowing: the loan you could repay while retaining an emergency fund and managing normal changes in your household budget.
These figures may be different. Your search budget should normally be based on the second one.
How to estimate your borrowing and monthly payment
Start with the property budget rather than the mortgage alone:
Available property budget = deposit + mortgage borrowing - buying costs and cash reserve.
Buying costs can include legal and conveyancing fees, searches, a survey, mortgage-related charges, removals, insurance and any applicable property tax. The exact amount depends on your circumstances, the property and the part of the UK in which you buy. Keep these costs separate from the deposit so you do not accidentally use every available pound to fund the purchase.
Next, estimate the mortgage payment. For a repayment mortgage, the payment depends on:
- the amount borrowed;
- the interest rate;
- the mortgage term; and
- the repayment type.
A longer term usually reduces the required monthly payment but can increase the total interest paid over the life of the mortgage. An interest-only mortgage has different eligibility requirements and does not reduce the capital unless a separate repayment plan is maintained.
For a useful worksheet, create three payment estimates:
- Illustrative payment: use the rate shown by your calculator or product research.
- Higher-rate payment: test what happens if the rate is higher at a future product change or remortgage.
- Reduced-income payment: review the budget assuming overtime, bonus or other variable income is not available.
Then add household costs that will continue after completion, such as council tax, energy, water, broadband, buildings or contents insurance, transport, childcare, maintenance and service charges. For a leasehold property, check the service charge and ground rent arrangements carefully rather than assuming they are negligible.
For wider context, compare your proposed mortgage with the costs of renting using Rent vs Buy in the UK. If you are ready to explore the wider process, see the step-by-step guide to buying a house in the UK.
Inputs and assumptions to collect
Use take-home income for your personal comfort check, but record gross income as well because lenders may assess income using their own policies. Include salary, regular guaranteed payments and any variable income separately. Do not assume that a lender will count bonuses, overtime, commission, self-employed profits or benefits in full.
List every regular commitment, including:
- credit-card balances and minimum payments;
- personal loans and car finance;
- student or postgraduate loan deductions;
- child maintenance or other financial commitments;
- hire purchase and subscriptions; and
- planned changes such as parental leave or a likely move.
Prepare details of your deposit, including whether it is savings, a gift, a Lifetime ISA withdrawal or another source. A larger deposit can reduce the loan-to-value ratio, but it should not leave you without money for emergencies, repairs and the purchase itself.
Your credit history also matters. Check that your credit files contain accurate personal details and account information, avoid taking unnecessary new credit while applying, and keep payments up to date. A strong credit record does not guarantee acceptance, and a limited credit history is not automatically a refusal, but errors should be corrected before an application where possible.
Finally, record assumptions beside every calculation: rate, term, repayment type, deposit, income included and monthly costs. This makes your worksheet reusable when one input changes.
Worked examples
These examples are illustrations only. They do not represent a quoted mortgage rate, a lender’s affordability limit or a prediction of future costs.
Example 1: building a purchase budget
Suppose a buyer has a deposit of £30,000 and estimates that buying costs, moving costs and a cash reserve require £8,000. If an affordability discussion suggests possible mortgage borrowing of £220,000, the working property budget would be:
£30,000 + £220,000 - £8,000 = £242,000.
The buyer should not treat £242,000 as an automatic target. They still need to test the mortgage payment alongside council tax, utilities, insurance, transport and maintenance. If that total leaves little monthly flexibility, a lower purchase price is more appropriate even if the lender’s maximum is higher.
Example 2: testing a monthly budget
Assume a repayment mortgage of £200,000 over a chosen term. The buyer records the payment produced by a mortgage calculator, then creates a second version using a higher assumed rate. They add fixed commitments and essential household costs to both versions.
If the first version leaves £700 each month after essential spending but the higher-rate version leaves only £150, the buyer should investigate whether that narrower margin is acceptable. They might increase the deposit, reduce the purchase price, consider a different term, or delay buying while building savings. The calculation does not predict what will happen; it exposes the risk of relying on a single favourable assumption.
When comparing products, look beyond the headline rate. Consider the initial period, fees, early repayment charges, portability, overpayment rules and what rate may apply afterwards. A mortgage comparison should reflect your likely plans, not just the lowest displayed payment.
When to recalculate
Affordability is not a one-off calculation. Revisit your worksheet whenever a major input changes, including:
- the interest rate or mortgage product you are considering;
- your deposit or emergency savings;
- your salary, working hours or employment status;
- your household size, childcare costs or plans for parental leave;
- your rent, debts, car costs or other regular commitments;
- the property price, service charge or estimated buying costs; or
- the end of an introductory mortgage period.
Recalculate before making an offer, again before submitting a full mortgage application and whenever the purchase takes longer than expected. If you change your deposit, borrow money, change jobs or take on new credit during the process, tell your broker or lender before relying on the previous figures.
A practical next step is to make a one-page affordability sheet with these headings: deposit, costs, reserve, proposed price, mortgage amount, rate, term, monthly payment, essential spending and higher-rate payment. Save the date and assumptions at the top. Review it monthly while searching and immediately after any change to your income or commitments.
Once the numbers are credible, you can move on to the offer and legal stages with greater confidence. Our guides on making an offer on a house and choosing a conveyancing solicitor explain what happens next.
