Buy-to-Let Mortgages in 2026: Stress Tests, Rates and the Stamp Duty Surcharge

The short answer

A buy-to-let mortgage funds a property you intend to rent out, not live in, and lenders treat that difference seriously. Expect to find a bigger deposit, a different affordability test built around the rent rather than your salary, and — in most cases — a higher interest rate than you'd get on a residential deal. Then, separately from the mortgage itself, the purchase also costs more in stamp duty: buy-to-let counts as an additional property, so the 5% second-home surcharge applies on top of standard rates, even if it's your very first rental purchase. None of this makes buy-to-let mortgages unusual or risky to arrange — it just means the numbers you'd use for a residential purchase don't transfer across.

Residential vs buy-to-let mortgages: what actually differs

The two aren't different versions of the same product — the whole basis of the lending decision changes:

The deposit: why buy-to-let asks for more upfront

Most buy-to-let lenders set a minimum deposit of 25% of the purchase price, capping the loan at 75% loan-to-value (LTV). A small number of lenders will go up to 80% LTV, but those deals typically come with a noticeably higher rate and larger arrangement fee, so the saving from a smaller deposit is partly clawed back through the cost of the loan itself. Lenders ask for more equity here because a rental property's income depends on a tenant actually being in place — void periods, maintenance costs and the ability to sell quickly if needed all make the loan inherently riskier than one secured against a home you live in and are personally committed to keeping up repayments on.

The rental income stress test, explained

Rather than assessing you mainly on personal income the way a residential lender would, buy-to-let lenders focus on whether the rent itself covers the mortgage, with a safety margin built in. This is measured as an interest coverage ratio (ICR) — gross annual rent divided by the annual interest cost at a stressed rate, expressed as a percentage.

• 125% ICR is the usual minimum for basic-rate taxpayers and for properties bought through a limited company.
• 145% ICR typically applies if any applicant is a higher- or additional-rate taxpayer, since Section 24 of the tax rules stops individuals deducting mortgage interest from rental profits before tax, leaving less income after tax to cover the loan.
• Houses in multiple occupation (HMOs) and larger multi-unit blocks often face stricter thresholds again, sometimes 165% or more, reflecting the extra management and voids risk.

The "stressed rate" itself is the other half of the test, and it's deliberately conservative: lenders generally use either a fixed notional floor — commonly somewhere around 5.5% to 6.5% — or your actual product rate plus a margin of roughly 2 percentage points, whichever produces the higher figure. That's regardless of how low your real pay rate is, because the test exists to check the mortgage would still be affordable if rates rose, not to reflect what you'll actually pay this year.

As a rough illustration: a £150,000 interest-only loan stressed at 5.5% produces about £8,250 a year in notional interest. At 125% ICR you'd need roughly £859 a month in rent to pass; at 145% ICR, a higher-rate taxpayer would need closer to £996 a month for the same loan. The gap between those two figures is entirely down to tax position, not anything about the property itself.

What buy-to-let mortgages actually cost

Buy-to-let rates sit above equivalent residential deals, and the gap can be substantial. Based on rates published in early October 2026, two-year fixed buy-to-let deals ranged from around 3.6% at lower LTVs up to the mid-4% range at 80% LTV, while five-year fixes ran from roughly 4.5% up to around 5.3% depending on LTV and lender — with the overall average fixed buy-to-let rate sitting close to 5.8%. Arrangement fees are also structured differently: rather than the flat few-hundred-pound fee common on residential deals, buy-to-let products frequently charge a percentage of the loan, often 3–5%, which adds a meaningful amount on a larger mortgage even before the interest is considered. These figures move with the wider mortgage market, so always check current rates with a broker or comparison site rather than relying on figures from an older article — including this one, over time.

The stamp duty surcharge stacks on top

Separately from the mortgage, the purchase itself attracts more stamp duty. Buy-to-let isn't a distinct stamp duty category — it's simply treated as an additional property, so in England and Northern Ireland you pay standard Stamp Duty Land Tax rates plus a flat 5 percentage point surcharge on the full purchase price, applied even to your first rental property if you already own your own home. On a £180,000 buy-to-let flat, for example, that's roughly £2,600 in standard SDLT plus a further £9,000 in surcharge — around £11,600 in total, due in cash at completion, on top of your deposit and any renovation budget. This cost isn't usually factored into the lender's affordability check, so it's worth budgeting for separately rather than discovering it late in the process. See our full second home and buy-to-let stamp duty guide for the complete bands across England, Scotland and Wales.

Buying as an individual or through a limited company

Many landlords, particularly those with more than one property, buy through a limited company rather than personally — mainly for tax reasons rather than mortgage ones, though it affects the mortgage too.

There's no single right answer — it depends on your tax band, how many properties you hold or plan to hold, and whether you need to draw the rental income out personally or can leave it to grow inside the company. This is genuinely worth a conversation with an accountant before you commit to either route, since reversing the decision later (moving a property into or out of a company) can itself trigger stamp duty and capital gains tax.

Getting approved: what actually helps

• A bigger deposit. Moving from 75% to 65% LTV typically unlocks noticeably better rates, on top of the lower borrowing itself helping you clear the stress test more easily.
• A realistic rental figure. Lenders will usually ask for independent evidence of achievable rent, often from a letting agent or surveyor, rather than just taking your own estimate.
• Clean existing credit. The same credit checks that apply to any mortgage apply here, and existing mortgage arrears make buy-to-let approval considerably harder.
• Manageable overall borrowing. If you already hold other buy-to-let mortgages, lenders will look at your whole portfolio's debt and rental cover, not just the new loan in isolation.
• A specialist broker. Buy-to-let criteria vary more between lenders than residential criteria do, so a broker who knows which lenders suit your specific situation — first-time landlord, portfolio landlord, limited company — can make a real difference to what's actually available to you.

Frequently asked questions

This guide is for general information and doesn't constitute financial advice. Buy-to-let deposit requirements, stress-test thresholds and mortgage rates vary by lender and change over time — always get a personalised illustration from a mortgage broker or lender, and confirm current stamp duty rates on GOV.UK, before deciding.