Buy-to-let mortgage guide 2026

A buy-to-let mortgage is a loan secured against a property that the borrower intends to let rather than live in. Because the income used to service the loan is rental income (rather than personal employment income), lenders assess buy-to-let applications using a different methodology from residential mortgages.

The primary test is the rental income stress test — the lender calculates whether the property's expected monthly rental income is sufficient to cover the mortgage payment, with a safety margin, at a stressed interest rate. The borrower's personal income is relevant as a background eligibility criterion (many lenders require a minimum income of £25,000) but is not the primary affordability metric.

Buy-to-let mortgages are not regulated by the Financial Conduct Authority in the same way as residential mortgages, with one exception: consumer buy-to-let, which applies where the landlord is letting to a close family member. This distinction affects the conduct requirements on lenders and brokers but does not materially change the product options available to most landlords.

The rental stress test is the most important calculation in a buy-to-let mortgage application. It determines whether the lender believes the property generates sufficient rental income to service the loan — and therefore how much they will lend.

The standard calculation is:

In practice: if monthly rent is £1,500, the lender uses a 5.5% stress rate and requires 125% rental coverage (ICR), the maximum interest payment they will allow is £1,500 ÷ 1.25 = £1,200/month. At 5.5% annual interest, a £1,200 monthly interest payment corresponds to a loan of approximately £261,000.

Interest coverage ratio (ICR)

The ICR is the ratio of rental income to interest payment that the lender requires. Most lenders set this at 125% for basic-rate taxpayers and 145% for higher-rate taxpayers — the higher requirement reflects the greater tax burden on landlords in higher tax brackets. Limited company borrowers are often assessed at 125% regardless of the director's personal tax position, because the company itself is the borrower.

Stress rate

The stress rate is the interest rate applied to the ICR calculation — it is typically higher than the actual mortgage rate to ensure the property remains viable if rates rise. Most lenders use either a fixed stress rate (commonly 5–5.5%) or the pay rate plus a buffer (e.g. pay rate + 2%). In a higher-rate environment, stress testing has become more restrictive: lenders at 5.5% stress are testing at a rate close to the actual market rate, which reduces maximum loan sizes compared to a low-rate environment.

Buy-to-let mortgages typically require a minimum 25% deposit (75% LTV). Some lenders will accept 20% (80% LTV) but the product range at that level is limited and rates are higher. The maximum LTV available in the buy-to-let market is typically 80%, compared to 95% for residential.

A larger deposit — 35% or more — materially improves the rates and lenders available, and is worth targeting if investment returns allow. For portfolio landlords with multiple properties, lenders assess overall LTV across the portfolio as well as on each individual property.

The deposit must typically come from the borrower's own resources — lenders are generally unwilling to accept gifted deposits for buy-to-let purposes. Deposits funded through equity release from another property, or a personal loan, are also restricted by most lenders (the latter is prohibited entirely — a personal loan cannot legally be used as a deposit for a buy-to-let purchase).

One of the most consequential decisions a buy-to-let investor makes is whether to hold property in their personal name or through a limited company (typically a Special Purpose Vehicle, or SPV). The right answer depends on your personal tax position, existing portfolio, long-term plans and the lender products available to you — there is no universal answer.

Personal name

Mortgage products are more widely available in personal names. Rates are sometimes lower. But rental profit is taxed at your marginal income tax rate (20%, 40% or 45%), and since 2020, Section 24 means mortgage interest relief is restricted to basic-rate tax relief only — a significant change for higher-rate taxpayers.

Limited company (SPV)

Rental profit within a limited company is subject to corporation tax (currently 25% for profits above £250,000, with marginal relief between £50,000 and £250,000 — and 19% for small profits under £50,000). Mortgage interest is fully deductible as a business expense, which removes the Section 24 restriction. For higher-rate taxpayers retaining profit within the company rather than extracting it, the tax comparison can be significantly in favour of the limited company structure.

However: limited company buy-to-let mortgages typically carry higher rates than personal-name equivalents, and there are fewer lenders operating in this space. Transferring personally-held property into a company triggers a stamp duty charge and potentially capital gains tax — making it expensive to switch later. If you are starting fresh with a new portfolio, the decision is more straightforward than if you have existing properties.

This is an area where tax advice from an accountant and mortgage advice from a specialist work together — the optimal structure depends on facts specific to your situation.

Section 24 of the Finance (No.2) Act 2015 phased out the ability for individual landlords to deduct mortgage interest from rental income before calculating their tax liability. It was fully implemented from the 2020/21 tax year. The impact was significant for higher-rate taxpayers.

Under the old rules, if a landlord earned £20,000 rental income and paid £15,000 mortgage interest, they paid income tax on £5,000. Under Section 24, they pay income tax on £20,000 (the full rental income) and receive only a basic-rate (20%) tax credit on the £15,000 interest — a tax credit of £3,000. For a higher-rate taxpayer, this is a significantly worse outcome: they owe 40% of £20,000 = £8,000, minus the £3,000 credit = £5,000 tax payable, compared to £5,000 × 40% = £2,000 under the old rules.

The practical response for many higher-rate landlords has been to restructure portfolios into limited company SPVs — where mortgage interest remains fully deductible. The decision to restructure needs to account for the stamp duty and CGT costs of transfer, which can be substantial for established portfolios.

Since September 2017, the Prudential Regulation Authority (PRA) requires lenders to apply enhanced underwriting to applications from portfolio landlords — those with four or more mortgaged buy-to-let properties. This changed how many lenders assess buy-to-let applications from experienced landlords.

Portfolio landlords must provide a full business plan covering the entire portfolio — not just the property being financed. This includes evidence of rental income, outstanding mortgage balances, void assumptions and management costs across every property. The lender assesses overall portfolio viability, not just the single application.

In practice, this made applying directly to mainstream lenders more cumbersome for portfolio landlords. Specialist buy-to-let lenders built processes specifically for portfolio applications and are often more efficient at handling the volume of documentation involved. An adviser experienced in portfolio lending makes a material difference at this stage.

The majority of buy-to-let mortgages are taken on an interest-only basis. The monthly payment covers only the interest on the loan — the capital balance does not reduce. At the end of the mortgage term, the full loan amount remains outstanding and must be repaid, typically through a property sale or refinance.

For investment purposes, interest-only has clear advantages: monthly payments are lower, maximising rental yield and the capital appreciation of the property (if any) is captured in full on sale. It also keeps the mortgage payment closer to the rental income on an interest-basis — the stress test calculates the loan size against interest payments, not repayment payments.

Repayment buy-to-let mortgages exist and may suit landlords who prefer to build equity progressively or who are closer to retirement and want the mortgage fully cleared. Monthly payments are higher, and the rental stress test may result in a lower maximum loan because repayment payments are higher than interest-only payments for the same loan size.

Not all properties are accepted by all lenders for buy-to-let purposes. Understanding the restrictions before you purchase avoids problems when applying for finance.

• HMOs (houses in multiple occupation). Properties let to three or more unrelated tenants sharing facilities require HMO buy-to-let products, which are distinct from standard BTL. Most mainstream lenders do not offer HMO mortgages — specialist lenders do.
• Student lets. Many lenders exclude properties let primarily to students. Specialist student accommodation lenders exist.
• Short-term holiday lets. Airbnb-style lets are not permitted on standard BTL mortgages. Holiday let mortgages have different underwriting based on projected occupancy.
• New build flats. Some lenders apply maximum LTV restrictions on new build flats (often capped at 75% even where 80% is the standard maximum) due to concerns about short-term value volatility.
• Properties above commercial premises. Flats above restaurants, takeaways or other commercial premises are often declined by mainstream lenders due to fire risk and valuation concerns.