What Landlords Need to Know About Buy-To-Let Affordability Tests in 2025

Buy-to-let landlords are facing a very different mortgage market in 2025 compared to even a few years ago. While demand for rental property remains strong, lenders have become far more cautious about how they assess whether your rental income can support the mortgage payments. Even seasoned portfolio landlords are finding that affordability tests can block refinancing or restrict how much they can borrow.

Understanding how these tests work, and what you can do to improve your chances of passing them, has never been more important.

What is a Buy-To-Let Affordability Test?

When you apply for a buy-to-let mortgage, the lender wants to be certain that the rent will cover the interest payments on the loan, with a buffer on top. This is known as the interest coverage ratio (ICR).

Typically, lenders require rental income to cover between 125% and 145% of the mortgage interest costs, depending on whether the property is owned personally or through a limited company.

Example:

• Mortgage interest = £800 per month.
• At 145% coverage, the lender needs rent of at least £1,160 per month.
• If your rent is lower than this, you may fail the affordability test, even if the property comfortably covers its costs in practice.

Why Do Lenders Stress Test Buy-To-Let Mortgages?

The stricter approach comes from Prudential Regulation Authority (PRA) rules introduced in 2017. These were designed to protect both lenders and borrowers in an environment of rising interest rates.

Lenders now run affordability calculations not at the rate you are actually applying for, but at a stress rate, often 2–3% higher. This means you could be applying for a deal at 5%, but the lender tests affordability as though the interest rate were 7%.

The intention is to ensure you can still service the mortgage if rates increase. While this makes sense from a regulatory perspective, it has created real challenges for landlords in today’s market.

How Different Lenders Apply the Rules

Not all lenders are equal in how they interpret the affordability rules. Key differences include:

• Limited company borrowing – many lenders apply a lower coverage ratio (125%) compared with personal applications (145%), which can make limited company borrowing more attractive.
• Stress rate applied – some lenders test at 5.5%, others at 7%, and a handful will even test at the actual product rate if you take a five-year fix.
• Rental calculation basis – a few lenders will accept projected rents (if supported by a letting agent letter), while most rely on the lower of actual or surveyor valuation.

Because of this variation, two landlords with identical circumstances could be approved by one lender and declined by another.

Worked Example: Passing or Failing the Test

Scenario: You are refinancing a property worth £200,000 with a £150,000 loan request.

• Rent: £950 per month
• Loan: £150,000
• Product rate: 5%
• Interest = £625 per month

Lender A (145% at 7%)
£150,000 × 7% = £10,500 annual interest (£875 monthly).
145% coverage = £1,268 required rent.
At £950, you fail the test.

Lender B (125% at product rate 5%)
£150,000 × 5% = £7,500 annual interest (£625 monthly).
125% coverage = £781 required rent.
At £950, you pass easily.

The difference is purely down to lender policy.

Common Pitfalls Landlords Face

• Low-yielding properties – flats in prime city centres often have lower yields but high capital growth. These can struggle under stress testing.
• Existing debt across a portfolio – lenders often review your whole portfolio, not just the property being refinanced. Weak spots can drag everything down.
• Unrealistic rental expectations – surveyors may value the rental income below what you are actually achieving, particularly if they use comparable evidence rather than your current tenancy agreement.
• High gearing – borrowing at 75% LTV or above puts more pressure on affordability compared with more conservatively geared properties.

How to Improve Your Chances of Passing

• Increase rents where tenancy agreements allow, raising towards market levels to strengthen your affordability case.
• Target lenders with lower stress rates; some specialist lenders assess five-year fixes at the pay rate rather than elevated stress rates.
• Restructure your borrowing by prioritising refinances on higher-yield properties first, or by using a limited company where appropriate.
• Clear personal debt to improve your overall financial profile.
• Seek specialist advice; brokers who focus on landlord finance know which lenders are pragmatic in specific scenarios.

Why 2025 Could Be a Turning Point

With inflation easing and base-rate expectations starting to shift, lenders may become more competitive in the months ahead. Already, some are softening stress test assumptions, particularly on longer fixes.

For landlords, the challenge is to balance today’s affordability hurdles with tomorrow’s opportunities. Those who can restructure intelligently now may be well placed to expand as the market stabilises.

Final Thoughts

Affordability tests are here to stay. They are not designed to frustrate landlords but to ensure long-term sustainability in the buy-to-let sector. By understanding how they work and positioning your portfolio accordingly, you can still access competitive finance in 2025.

Speak to Our Sponsor

Every landlord’s circumstances are different. Some lenders will test your application harshly, others more pragmatically. Our sponsor works daily with landlords to run affordability calculations, match them with suitable lenders, and identify opportunities to save money or release equity.

Publication date: Monday, 1 September 2025