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Buy-to-let mortgage for landlords: how they work in 2026
March 4, 2026
Financing a rental property is different from buying a home to live in, and getting the mortgage right is one of the most consequential decisions you will make as a landlord. The product type, deposit size, lender criteria, and timing of your remortgage all affect how much you earn from your investment over its lifetime. This article explains how buy-to-let mortgages work, what lenders actually look at when they assess your application, and how to navigate the key decisions, from your first purchase through to remortgaging a growing property portfolio.
Before you run the numbers, use the August buy-to-let mortgage calculator to work out your monthly costs and how much you might be able to borrow based on expected rental income.
What makes a buy-to-let mortgage different
A buy-to-let (BTL) mortgage is specifically designed for properties you intend to rent out rather than live in yourself. You cannot use a standard residential mortgage for a rental property. Using one would breach your mortgage terms and could result in the lender demanding immediate repayment.
Lenders treat buy-to-let lending as a form of business borrowing rather than consumer credit, which has a number of practical implications. Most BTL mortgages are not regulated by the Financial Conduct Authority (FCA), which means you have fewer automatic consumer protections than with a residential mortgage. There are exceptions, if you rent to a close family member, for example, FCA regulation typically applies, but for standard buy-to-let to unrelated tenants, lenders operate under their own criteria rather than a prescribed regulatory framework.
The other major practical difference is how affordability is assessed. For a residential mortgage, your personal income is the primary measure. For a buy-to-let mortgage, the rental income the property is expected to generate takes centre stage, though lenders often also require evidence of personal income above a minimum threshold (usually £25,000 per year).
Deposits are also larger. While residential mortgages can be arranged with as little as a 5% deposit, buy-to-let lenders typically require a minimum of 25% of the property value. That higher deposit reduces the lender's risk and usually gives you access to better interest rates, but it also means a significant amount of capital tied up before you receive a single pound of rent.
Interest-only vs repayment: understanding the choice
Most buy-to-let landlords choose an interest-only mortgage, and for good reason. Understanding why requires looking at how the two types work in practice.
With an interest-only mortgage, you pay only the interest charged on the loan each month. The original amount you borrowed — the capital — stays the same throughout the mortgage term and must be repaid in full at the end, whether through selling the property, using savings, or remortgaging. If you borrow £200,000 on a 25-year interest-only term at 5%, your monthly payment is £833. At the end of 25 years, you still owe £200,000.
With a repayment mortgage, you pay both interest and a portion of the capital each month, so the loan balance reduces over time. By the end of the term, you own the property outright and owe nothing. On the same £200,000 at 5%, your monthly repayment would be around £1,170. Higher monthly outgoings, but a clean exit at the end.
The case for interest-only in a buy-to-let context is largely about cash flow. Lower monthly payments mean a higher chance that rental income comfortably covers the mortgage, which improves your rental yield and reduces your personal exposure in void periods. Landlords who take a long-term investment view typically expect to sell the property at a profit when the term ends, using the proceeds to repay the capital and pocket the growth.
The risk is clear, however. If property values fall, you could sell for less than you owe. If your planned exit does not materialise, you face a large lump sum at term end with no obvious source. Lenders now require borrowers to demonstrate a credible repayment strategy — sale of the property, a pension, savings, or other investments — rather than simply deferring the question indefinitely.
Repayment mortgages suit landlords who want to build equity progressively, perhaps because the property is intended as a long-term asset to pass on or a retirement income source. Monthly costs are higher, which squeezes cash flow and may reduce your ability to acquire additional properties, but there is no capital exposure at term end.
A middle path exists too. Some lenders offer part-and-part mortgages, where you repay a portion of the capital each month while keeping payments lower than a full repayment arrangement. It is a less common product but worth exploring if you want to reduce end-of-term exposure without committing to full repayment costs.
How lenders calculate what you can borrow
The central calculation in buy-to-let lending is the interest coverage ratio (ICR). This measures whether your expected rental income is sufficient to cover the mortgage interest, with a margin for costs and risk.
The ICR is calculated at a stressed rate — not the actual rate on your mortgage product — to ensure you could still afford payments if interest rates rise. Lenders typically apply a stress rate of between 5.5% and 8%, depending on the lender and product type, even if your actual mortgage rate is considerably lower. This explains why a property that appears to generate excellent returns on a simple yield calculation may still fail a lender's affordability test.
The minimum ICR most lenders require is 125% for basic rate taxpayers and borrowers using a limited company structure, meaning the rent must cover at least 125% of the stressed monthly interest. For higher rate taxpayers borrowing personally, most lenders require 145%, reflecting the fact that mortgage interest relief is restricted under Section 24 rules and their net income from the property is lower. The effect is that landlords paying the 40% or 45% tax rate face a higher bar to borrowing than those in the basic rate band.
There is a notable exception when it comes to five-year fixed rate products. The PRA permits lenders to apply their stress test at the actual mortgage rate (rather than a higher stressed rate) when the fix period is five years or longer. This makes five-year fixes significantly more affordable from an ICR perspective and is one reason they are by far the most common choice in the market.
Where rental income alone does not meet the ICR requirement, some lenders allow what is known as top-slicing. This means they take personal income into account to bridge the shortfall, accepting that a landlord's earnings outside the property can cover any gap between stressed interest and rental income. Top-slicing is typically reserved for higher-income borrowers and is not universally available.
Understanding loan-to-value and its impact on rates
Loan-to-value (LTV) — the proportion of the property value you are borrowing — has a direct effect on the interest rate you will pay. The more equity you have, the lower the risk to the lender and the cheaper the rate.
The sweet spot for most buy-to-let landlords is 75% LTV (a 25% deposit), which gives access to the widest range of products and the most competitive rates. Moving to 80% LTV is possible with some lenders but typically attracts meaningfully higher rates and stricter criteria. Products above 80% LTV are rare in the buy-to-let market.
For landlords with existing properties, remortgaging or purchasing can sometimes be structured to take advantage of equity built up through capital growth or repayments, pushing down the effective LTV and unlocking better terms. This is one practical reason why understanding your portfolio's overall loan-to-value position matters as much as the position on any individual property.
Portfolio landlord rules: what changes at four properties
If you hold four or more mortgaged buy-to-let properties, you are classified as a portfolio landlord under rules introduced by the Prudential Regulation Authority (PRA) in 2017. This classification triggers additional underwriting requirements that apply across your whole portfolio, not just the property you are trying to mortgage.
Lenders who accept portfolio landlords — and not all do — will typically require a full portfolio schedule detailing every property you own, its current value, the outstanding mortgage, the monthly rent, and the loan-to-value position. They will then stress-test the portfolio as a whole, applying their ICR requirements across all your properties simultaneously. If a weaker property in your portfolio does not pass the stressed ICR test, it can block your ability to borrow on an otherwise strong new acquisition.
This creates a practical challenge: your worst-performing property can prevent you from growing your portfolio, even if every new purchase would stand on its own merits. Addressing this usually means either selling the underperforming asset, remortgaging it to reduce the monthly interest, or increasing its rent to improve coverage before applying for new borrowing.
Some lenders also request a business plan explaining your investment strategy, and most require at least two years of experience as a landlord before they will lend to portfolio borrowers. Specialist lenders such as Paragon and Landbay have built their businesses around portfolio landlord lending; mainstream high-street lenders tend to be more conservative or have exited this segment altogether.
The HMO market adds another layer of complexity. Houses in Multiple Occupation require specific mortgage products with their own underwriting criteria, often including higher minimum deposits and additional scrutiny of licensing compliance.
Fixed, variable, and tracker rates
Buy-to-let mortgages come in the same product types as residential mortgages. The key options are fixed rates, tracker rates, and standard variable rates (SVR).
A fixed rate locks your interest rate for a set period — typically two or five years — giving certainty over monthly costs during the fixed term. At the end of the fixed period, you move to the lender's SVR (which is invariably higher) unless you remortgage. Five-year fixes dominate the market partly because of the stress-testing advantage described above.
A tracker mortgage follows the Bank of England base rate with a set margin added on top. Trackers move up and down with the base rate, which means lower payments when rates fall but higher payments when they rise. They suit landlords who believe rates will fall and who want to benefit from that movement without penalty charges for early exit.
The SVR is the default rate you pay when a fixed or tracker deal expires. It is almost always higher than the market rate for new products and offers no rate certainty. Very few landlords deliberately choose the SVR; it is usually a position you land in when a deal expires without an active remortgage in place.
Most experienced landlords set a reminder to begin the remortgage process three to six months before their current deal expires, giving enough time to compare the market, submit an application, and complete before they slide onto the SVR.
How to remortgage a buy-to-let property
Remortgaging a buy-to-let property is the process of switching your mortgage to a new deal at the end of a fixed or tracker period, either with your existing lender (a product transfer) or with a different lender. It is one of the most important financial decisions you make as a landlord, and one that many landlords handle reactively rather than proactively.
The starting point is knowing your current mortgage end date and your current LTV. If property values in your area have risen since you bought, your LTV may be lower than when you first borrowed, which could qualify you for a cheaper rate tier. If you have been on a repayment mortgage or have made overpayments, the effect is the same.
When comparing remortgage options, look beyond the headline rate. Arrangement fees, valuation costs, legal fees, and early repayment charges all affect the true cost of switching. A mortgage with a higher rate but no arrangement fee can work out cheaper over the fixed term than one with a low rate and a £2,000 fee, particularly on smaller loan sizes.
For portfolio landlords, a remortgage triggers the full portfolio stress test described above. This can catch landlords off guard, particularly those who have never had to present a full portfolio schedule to a lender before. Preparing this documentation in advance, knowing your total portfolio LTV, rent roll, and monthly interest across every property, puts you in a much stronger position when lenders ask.
The remortgage market for buy-to-let has been active in recent years. A large number of five-year fixed deals taken out during the low-rate period of 2019 to 2021 have been maturing, pushing many landlords into a higher-rate environment than they experienced during their initial fixed term. Average two-year buy-to-let fixed rates in late 2025 were around 4.9%, and five-year fixes around 5.2%, compared with sub-2% deals that were common in 2020. For landlords remortgaging off those historic deals, understanding whether the revised costs still stack up against rental income is essential before committing to a new product.
The impact of higher rates on rental yield is one reason good record-keeping matters so much. Understanding your actual net rental yield, not just the gross rent, requires clean data on all your costs, including the mortgage. August's rent tracking and expense management tools are designed to give you exactly that picture, property by property.
Section 24 and what it means for your mortgage choice
No guide to buy-to-let mortgages in 2025 would be complete without addressing mortgage interest relief and Section 24. Since April 2020, individual landlords who hold property in their own name can no longer deduct mortgage interest from rental income before calculating their tax bill. Instead, they receive a basic rate (20%) tax credit on their finance costs.
The effect for higher rate taxpayers is significant. A landlord paying 40% income tax who has substantial mortgage interest costs pays tax on their gross rental income, then receives only a 20% credit. The result is a higher effective tax rate on profits than the headline income tax rate suggests. For some highly leveraged landlords, Section 24 has turned paper profits into real losses.
This is a key reason why limited company buy-to-let has grown substantially. Companies are not subject to Section 24 and can still deduct mortgage interest as a business expense before calculating corporation tax. The trade-off involves higher mortgage rates on company products, Stamp Duty Land Tax on incorporation of an existing portfolio, and the cost of extracting profits from the company as dividends. Whether incorporation makes sense depends heavily on individual circumstances, portfolio size, and tax position, and requires detailed professional advice.
It is also directly relevant to mortgage affordability. The lender's ICR requirement of 145% for higher rate taxpayers reflects this tax reality and the lower net income it produces. Understanding how Section 24 affects your tax position is therefore not a separate exercise from understanding your mortgage, they are closely connected.
Consent to let: a note for accidental landlords
Some landlords do not set out to build a portfolio. They need to move for work, cannot sell in a sluggish market, or inherit a property they want to let out temporarily. If you are in this situation and the property already has a residential mortgage, you will need consent to let from your lender before you can legally rent it out. Letting without consent can breach your mortgage terms and potentially trigger demands for immediate repayment.
Consent to let is a temporary permission, typically granted for one to two years with conditions attached. Most lenders charge a higher interest rate, add an administration fee, and require that you hold appropriate landlord insurance. It is not a long-term solution. If you intend to let the property for more than a year or two, switching to a proper buy-to-let mortgage is usually the more appropriate step.
Practical checklist before applying
Running through these considerations before you approach a lender will put you in a significantly stronger position:
Know your expected rental income - speak to local letting agents to get a realistic current market figure, not an optimistic estimate.
Check whether it passes the ICR test - use the August buy-to-let mortgage calculator to model the numbers under typical stress test conditions.
Understand your tax position - if you pay income tax at the higher rate, a 145% ICR applies and your borrowing capacity is lower than a basic rate taxpayer's.
Have your documents ready - lenders will want three months of bank statements, proof of income, and for portfolio landlords, a full schedule of your existing properties.
Factor in all costs - arrangement fees, valuation, legal costs, and buildings insurance all affect the true return from the investment.
Build in a buffer - void periods are a reality of letting property. A mortgage that only works when the property is fully occupied is a mortgage that will create stress when it inevitably is not.
Whether you are financing your first buy-to-let or remortgaging a portfolio that has been in place for years, understanding how lenders think is the foundation of good planning. The August buy-to-let mortgage calculator gives you a working starting point; a qualified mortgage broker who specialises in buy-to-let will take you the rest of the way.
Disclaimer: This article is a guide and not intended to be relied upon as legal, financial or professional advice, or as a substitute for it. August does not accept any liability for any errors, omissions or misstatements contained in this article. Every effort was made to be accurate at the time of writing. Always speak to a suitably qualified professional, including a regulated mortgage adviser, before making borrowing decisions.
Author
August Team
The August editorial team lives and breathes rental property. They work closely with a panel of experienced landlords and industry partners across the UK, turning real-world portfolio and tenancy experience into clear, practical guidance for small landlords.
