Buy-to-Let Mortgages Explained: 2026 Guide

If you've only ever had a residential mortgage, a buy-to-let (BTL) mortgage can feel like a different world. The way lenders assess you, the deposit they expect, the rates on offer and the questions they ask are all built around a different idea: that the property itself, through its rental income, is what's really being lent against. This guide walks through how BTL mortgages actually work, what lenders look for, and what to budget for, so you can approach the process with realistic expectations.

How a BTL mortgage differs from a residential one

With a residential mortgage, a lender looks mainly at your personal income, outgoings and credit history to decide how much you can borrow and afford to repay. A buy-to-let mortgage flips that emphasis. Lenders are primarily interested in whether the property's expected rental income will comfortably cover the mortgage interest, with your personal income and circumstances treated as a secondary factor (and, for some lenders, barely considered at all once a minimum income threshold is met).

That different emphasis shows up in three practical ways almost every new landlord notices: deposits are usually higher, typically 25% of the property's value or more, rather than the 5% to 10% sometimes possible on residential deals; interest rates and arrangement fees tend to run a little higher than equivalent residential products, reflecting the lender's view that BTL lending carries more risk; and the whole application leans heavily on the rental figures, often requiring a letting agent's assessment of achievable rent before a lender will even produce a mortgage offer.

Interest-only vs repayment

Most BTL mortgages can be arranged on either an interest-only or a capital repayment basis, and the choice has a big effect on monthly cashflow.

With an interest-only mortgage, your monthly payment covers only the interest charged on the loan. The capital balance never reduces on its own, and you still owe the full amount borrowed at the end of the term. Many landlords choose this route because it keeps monthly payments significantly lower, improving cashflow in the meantime, with the expectation that the capital will eventually be repaid from selling the property, refinancing, or other savings and investments built up over the years. The important thing is to go in with your eyes open: an interest-only mortgage only works well if you have a credible plan for repaying the capital when the term ends. Without one, you can find yourself facing a large lump sum you're not in a position to pay, which is a genuine risk worth planning for from day one.

A repayment (capital and interest) mortgage costs more each month because part of every payment reduces the loan balance, but it guarantees the mortgage will be cleared by the end of the term provided payments are kept up. Some landlords prefer this certainty, particularly on properties they intend to hold for the long term as part of a retirement plan, even though it does reduce monthly cashflow along the way.

How lenders assess affordability: the Interest Coverage Ratio

This is the part that catches most first-time BTL borrowers off guard. Rather than using income multiples the way residential lenders often do, BTL lenders typically apply an Interest Coverage Ratio (ICR) test, sometimes called a rental cover or stress test. In simple terms, they want to see that the rental income would comfortably exceed the mortgage interest, with some headroom built in for void periods, maintenance, letting agent fees and rate rises.

As a general guide, many lenders look for rental income to cover the mortgage interest by around 125% for basic-rate taxpayers, rising to roughly 145% for higher-rate taxpayers (who, under Section 24, get less tax relief on their mortgage interest and so need a bigger cushion). Crucially, lenders usually don't test this against the actual pay rate on the mortgage. Instead they apply a "stressed" rate, often the pay rate plus around 2 percentage points, subject to a floor commonly somewhere around 5.5%, to make sure the numbers would still work if interest rates rose. A mortgage with a low headline rate can therefore still fail the lender's test if the stressed rate pushes the required rental cover above what the property can realistically achieve.

It's worth being clear that these figures (125%/145%, the +2% stress margin and the 5.5% floor) are typical, indicative figures rather than universal rules. Every lender sets its own ICR thresholds, stress rates and floors, and they can and do change these over time depending on market conditions and their own appetite for risk. Some lenders are notably more generous than others, which is one of the main reasons the broker landscape (covered below) matters so much. To see how this plays out against your own numbers, our BTL Mortgage Affordability Calculator applies the standard ICR approach to a given rental income so you can get a feel for the kind of loan size that's likely to be supportable, and the rent you'd need for a particular loan amount.

Deposit requirements

The most common minimum deposit for a buy-to-let mortgage is around 25% of the property's value, though this varies. Some lenders will consider deposits as low as 20%, particularly for strong applicants with existing portfolios and healthy rental cover, while others require considerably more for properties they see as higher risk, such as houses in multiple occupation (HMOs), new-build flats, properties above commercial premises, or non-standard construction. If you're considering any of these property types, it pays to budget for a larger deposit and expect a smaller pool of lenders to choose from.

Fees to budget for

The interest rate is only part of the cost of a BTL mortgage. When comparing deals and working out your true cost of borrowing, it's worth setting money aside for:

• Arrangement or product fees. Often charged as a flat amount or a percentage of the loan, sometimes running into thousands of pounds on larger loans. These can usually be added to the loan or paid upfront, and it's worth comparing both ways since adding them increases the amount you pay interest on.
• Valuation fees. The lender will want the property valued to confirm it's suitable security for the loan, and to check the rental assessment is realistic.
• Legal fees. Conveyancing costs for the purchase (and the mortgage itself) apply just as they would on a residential purchase.
• Broker fees. If you use a mortgage broker (often a sensible move, see below), they may charge a fee for their service on top of any commission they receive from the lender.

Stamp duty is a separate, often substantial cost on top of all this. If you haven't already, it's worth working through our Buy-to-Let Stamp Duty Guide to understand what you'll owe before you commit to a purchase.

Fixed vs variable and tracker rates

As with residential mortgages, BTL deals typically come as either fixed rate (the rate stays the same for an agreed period, commonly two or five years, giving you certainty over your monthly payments) or variable and tracker rate (the rate moves, often in line with the Bank of England base rate plus a margin, meaning your payments can rise or fall over time). Fixed rates suit landlords who value predictable cashflow and want to plan with confidence, particularly if their rental cover is tight. Trackers and variable deals can work out cheaper when rates are falling or already low, but they carry the risk that payments rise, sometimes significantly, if rates increase. There's no universally "right" answer here: it comes down to your appetite for risk, how tight your rental cover is, and your wider financial plans.

Limited company buy-to-let mortgages

If you own, or are considering owning, property through a limited company, you'll need a mortgage product designed for that structure rather than a personal-name BTL mortgage. These exist and are well established, but the pool of lenders offering them is generally smaller than for personal-name lending, and the rates and fees can differ, sometimes being slightly higher to reflect the more specialist nature of the lending. If incorporation is something you're weighing up, it's worth factoring mortgage availability and cost into that decision alongside the tax position. Our Ltd Company vs Personal Calculator can help you compare the overall numbers.

Why a specialist BTL broker is usually worth using

The buy-to-let lending market is genuinely fragmented. ICR thresholds, stress rates, acceptable property types, treatment of portfolio landlords, attitudes to limited companies and HMOs, and pricing all vary significantly from one lender to the next, and shift over time as lenders adjust their appetite for risk. A broker who specialises in buy-to-let, rather than a generalist who occasionally arranges one, will typically know which lenders are likely to look favourably on your particular situation, which can save real time, and in many cases real money, compared with applying directly and hoping for the best. This is especially valuable if your situation is anything other than straightforward, for example if you're buying through a limited company, building a larger portfolio, or considering a non-standard property.