Buy-to-Let Mortgages: What Is a Buy-to-Let Mortgage?
Starting With the Basics
If you have ever thought about buying a property to rent out, you will have come across the term "buy-to-let mortgage". It sounds technical, but the idea behind it is simple: it is a loan for a property you plan to rent to someone else rather than live in yourself.
This guide walks through what these mortgages are, how lenders decide what you can borrow, and what to weigh up before you commit. No jargon, no pressure - just clear information so you can decide whether it fits your plans.
Who This Guide Is Written For
This is for anyone in the UK considering becoming a landlord for the first time, existing landlords thinking about refinancing, and anyone who has inherited or is thinking of keeping a second property and renting it out. It is also useful if you simply want to understand how landlord borrowing differs from a normal home loan.
What a Buy-to-Let Mortgage Actually Is
A buy-to-let mortgage is a loan secured against a property you intend to rent out rather than occupy. MoneyHelper describes it as the mortgage you use when buying an investment property to let to tenants, and Barclays explains that these products are designed specifically for properties intended to be rented to others, with expected rental income usually helping to determine how much you can borrow.
That last point is the key difference. A residential mortgage is broadly assessed on your personal income and outgoings. A buy-to-let mortgage is assessed largely on whether the property's rent can comfortably cover the mortgage interest, with your own circumstances acting as a supporting check rather than the main test.
The defining feature is intended use, not ownership. Owning a second home does not automatically make it a buy-to-let. Renting it out to tenants does.
The property has to work financially on its own terms, not just on yours.
How Lenders Decide What You Can Borrow
Most lenders start with the rent. They apply a stress test to check that projected rental income exceeds the mortgage interest by a healthy margin, often expressed as an interest cover ratio. UK Finance reported an average buy-to-let interest cover ratio of 218% in Q4 2025, up from 201% a year earlier, meaning rental income was more than twice the interest cost on average. Lower rates and firmer rents have both helped that figure improve.
Deposits are larger than most people expect. MoneySuperMarket puts typical buy-to-let deposits at 25% to 40% of the property value, so loan-to-value ratios are lower than on many residential deals.
Many buy-to-let mortgages are interest-only, which keeps monthly payments lower but leaves the capital outstanding at the end of the term. Fixed rates dominate: UK Finance counted 1.46 million outstanding fixed-rate buy-to-let mortgages in Q4 2025, around 2% more than a year earlier, while variable-rate loans fell 9.8% to 466,000. That is why remortgage timing matters so much to landlords.
Why Landlords Still Use Them in a Higher-Rate Market
The short answer is the gap between rental yields and borrowing costs. Finder reported an average UK buy-to-let rental yield of 7.15% in Q3 2025, and UK Finance put it at 7.18% in Q4 2025, up from 6.99% a year earlier. Average interest rates on new buy-to-let loans were 4.77% in Q4 2025 - down 8 basis points on the quarter and 32 basis points on the year - falling again to 4.71% in Q1 2026 according to Mortgage Soup.
That spread between income and interest is a large part of the investment case, and it explains why rental income rather than house price growth alone tends to drive landlord decisions.
Activity has held up too. UK Finance recorded 59,489 new buy-to-let loans worth £11.2 billion in Q4 2025, up 18.2% by number and 21.3% by value year on year, followed by 58,272 loans worth £10.8 billion in Q1 2026. Much of that growth came from remortgaging rather than new purchases, which tells you a lot about how the market is behaving.
Weighing the Upsides Against the Trade-Offs
| Potential advantages | Potential drawbacks |
|---|---|
| Rental income can exceed mortgage interest, with average yields around 7.15%-7.18% in late 2025 | Deposits of 25%-40% tie up significant upfront capital |
| Interest-only options keep monthly outgoings lower | The capital balance still needs repaying at the end of the term |
| Fixed rates reduce short-term payment volatility | Rate risk returns at every remortgage point |
| Lending is assessed mainly on rental income, not just salary | Rental stress tests can limit how much you borrow |
| A live, competitive market with active lender choice | Void periods, arrears and repairs can interrupt income |
| Possible capital growth over the long term | Possessions rose 10% year on year to 770 in Q4 2025 |
Points Worth Checking Before You Apply
Eligibility rules are not uniform, and this catches people out. Nationwide, for example, requires applicants to be 21 or over, to have at least three years of UK address history, to already own a property in the UK or apply with someone who does, and to be buying in England, Wales or mainland Scotland, with minimum borrowing of £25,001. Barclays takes a different view on some of those points, including allowing applicants who do not already own a residential property. Comparing lender-specific criteria is essential rather than optional.
Risk deserves a realistic look too. UK Finance recorded 9,520 buy-to-let mortgages in arrears of more than 2.5% of the balance at the end of Q4 2025, down 910 on the quarter - an improving picture. Yet possessions rose to 770, up 10% year on year. Arrears pressure eased overall, but some landlords still hit serious repayment stress.
Build in a buffer for void periods, maintenance and a higher rate at your next remortgage.
Other Routes to Consider
- Consent to let - If you already have a residential mortgage and want to rent your home out temporarily, your existing lender may grant permission instead of requiring a new product.
- Let-to-buy - Refinancing your current home onto a buy-to-let basis while buying a new home to live in.
- Holiday let mortgages - Designed for short-term lettings, assessed on seasonal income patterns rather than a standard monthly rent.
- Limited company buy-to-let - Borrowing through a company structure, which some landlords use for tax and portfolio reasons. Independent tax advice is important here.
- Property funds or REITs - Indirect exposure to property returns without owning, managing or borrowing against bricks and mortar.
- Cash purchase or lower gearing - Buying with a larger deposit or no mortgage at all reduces interest cost and rate risk, though it ties up more capital.
Common Questions Answered
Can I live in a property I bought with a buy-to-let mortgage? No. These products are intended for properties let to tenants. Living there would usually breach your mortgage terms, so speak to your lender if your plans change.
How big a deposit will I need? Typically 25% to 40% of the property value, according to MoneySuperMarket, though the exact figure depends on the lender and the deal.
Do I need to be a homeowner already? Some lenders require it. Nationwide asks that you already own a UK property or apply with someone who does, while Barclays can consider applicants who do not. It varies by lender.
Are buy-to-let rates higher than residential rates? Generally yes, though they have eased. Average new buy-to-let rates were 4.77% in Q4 2025 and 4.71% in Q1 2026.
What is an interest cover ratio? It measures how far rental income exceeds mortgage interest. The average was 218% in Q4 2025, meaning rent was more than double the interest cost.
Is buy-to-let regulated by the FCA? Most buy-to-let lending is unregulated, although "consumer buy-to-let" cases can be regulated. Always check the status of any product you are offered.
Where Kandoo Fits In
Kandoo is a UK finance broker, and our role is to help you understand your options clearly before you commit to anything. We can talk you through how lenders assess rental income, what deposit levels are realistic, and where eligibility criteria differ between providers, so you can compare like with like. There is no pressure and no assumptions - just straightforward guidance to help you decide whether buy-to-let genuinely suits your circumstances.
Important Information
This article is general information, not personal financial, tax or legal advice. Buy-to-let lending is often unregulated, criteria and rates vary by lender, and market data referenced here reflects specific periods and may since have changed. Your property may be repossessed if you do not keep up repayments. Please seek independent advice tailored to your own situation before making any decision.
Buy now, pay monthly
Buy now, pay monthly