How to assess your affordability when taking out a mortgage

A mortgage is usually the biggest financial commitment many people make. Even if you can borrow what a lender offers, it doesn’t always mean the repayments will comfortably fit your day-to-day life—especially if your circumstances change or interest rates move.

Assessing affordability before you apply can help you:

• focus your search on homes you can realistically afford
• avoid stretching your budget
• understand what happens if your mortgage payments rise

What affordability checks look like from a lender

When you apply for a mortgage, lenders carry out affordability assessments. While the exact approach varies, most checks broadly consider:

1) Your income and regular outgoings

Lenders typically look at your income (for example, salary and other verified earnings) alongside committed monthly spending.

Outgoings may include items such as:

• existing loan and credit commitments
• credit card minimum payments
• childcare costs
• maintenance payments
• other regular financial obligations

The aim is to understand whether you have enough surplus income after essential costs to meet mortgage repayments.

2) Your ability to cope if interest rates increase

Many mortgages are on variable, tracker, or other rate structures where repayments can change. Lenders may therefore assess affordability under a higher interest rate scenario.

This is designed to test whether you could still make payments if rates rise—rather than assuming today’s rate will stay the same.

3) Your credit report and repayment history

Lenders use your credit report to understand how you’ve managed credit in the past and whether there are any negative markers.

It’s important to note that a less-than-perfect credit profile doesn’t automatically rule you out, but it can affect how lenders view risk and what options are available.

4) Bank statement information and spending patterns

Some lenders may review bank statements to understand your day-to-day financial behaviour.

They may look for potential “red flags”, such as:

• frequent reliance on overdrafts
• regular payments to payday lenders
• patterns of gambling spending
• unusual or inconsistent income deposits

These checks are intended to provide a clearer picture of affordability beyond what’s written on an application.

Why doing your own affordability assessment matters

A lender’s affordability test is only one part of the picture. Your own assessment helps you judge whether the mortgage is sustainable for your lifestyle and priorities.

Running your own affordability check can also highlight practical questions before you commit, such as:

• How much will you have left each month after mortgage payments?
• Will you still be able to save for emergencies?
• Can you maintain other goals (retirement saving, family costs, or planned spending)?

How to assess affordability yourself: a practical approach

Step 1: Build a realistic monthly budget

Start with your current spending and separate it into:

• essential costs (housing bills, utilities, transport, groceries)
• financial commitments (existing debts, childcare)
• discretionary spending (entertainment, eating out)

Then add the mortgage payment you expect to pay, including any likely changes if your rate is not fixed for the full term.

Step 2: Calculate your “surplus” rather than just affordability

Instead of focusing only on whether you can technically make repayments, work out how much money you’d have left each month.

A useful mindset is to ask:

• What would happen if one bill increased?
• Could you still cover repayments if income reduced temporarily?
• Would you be able to keep saving?

Step 3: Consider the impact of rate changes

Even if you’re aiming for a particular deal, it’s sensible to stress-test your budget.

You can do this by estimating what your repayments might look like if interest rates rise, particularly if you’re considering a variable or tracker product.

This helps you understand whether you have a buffer—so you’re not relying on repayments staying exactly where they are today.

Step 4: Factor in the full cost of homeownership

Mortgage repayments are only part of the overall monthly cost.

When planning affordability, also consider:

• buildings insurance
• contents insurance (if applicable)
• council tax
• service charges (for flats or leasehold properties)
• maintenance and repairs

If you’re moving from renting, remember that some costs may change or increase.

Step 5: Check your credit information before you apply

Reviewing your credit file can help you spot inaccuracies or issues that may affect how lenders assess you.

If you find errors, correcting them can be beneficial before you submit an application. While credit scores aren’t the only factor lenders consider, the information in your report can influence outcomes.

Mortgage in principle: what it can and can’t do

A mortgage in principle (sometimes called an agreement in principle) can give you an early indication of how much you may be able to borrow.

It can be useful because it may help you:

• understand likely repayment levels for the borrowing range
• plan your property search with more confidence
• compare how different borrowing amounts affect affordability

However, it’s not the same as a full mortgage offer. Lenders may request further information and carry out more detailed checks before making a final decision.

Using calculators to stress-test your budget

Online mortgage calculators can help you model different scenarios, such as:

• changing the mortgage term
• adjusting the interest rate assumption
• comparing repayment amounts between options

While calculators can’t replicate every lender’s assessment, they’re a practical way to understand how sensitive your budget is to changes in repayments.

Balancing homeownership with other long-term goals

Affordability isn’t only about making payments—it’s also about having enough room for the rest of your life.

When you assess affordability, consider how the mortgage affects your ability to:

• build an emergency fund
• save for retirement
• plan for major expenses (such as education costs or home improvements)
• handle life changes without financial strain

A mortgage that fits comfortably today is generally more likely to remain manageable if your circumstances evolve.

Key takeaways

• Lenders assess affordability using income, outgoings, credit information, and sometimes bank statement patterns.
• Many assessments include a stress test for possible interest rate increases.
• Your own affordability check helps you judge sustainability for your lifestyle and priorities.
• Mortgage in principle can provide an early borrowing indication, but it isn’t a guarantee.
• Calculators can help you understand how changes in term or rate may affect repayments.

Important note

This guide is for general information only and does not constitute regulated financial advice. Your home may be repossessed if you do not keep up repayments on your mortgage or any other loans secured on it.