How much you can borrow on a buy-to-let is driven mainly by the rent the property can achieve, not your salary, which surprises many first-time landlords. This guide explains how much you can borrow on a buy-to-let: the rental cover calculation, the loan-to-value cap, and the factors that can increase or limit your borrowing.
Driven by rental income
The amount you can borrow on a buy-to-let is determined largely by the rental income the property is expected to produce, which must cover the mortgage interest by a set margin. This is quite different from a residential mortgage based on your earnings. So the first question is not how much you earn, but how much rent the property can achieve, as our guide to buy-to-let rental cover explains.
The rental cover calculation
Lenders work out your maximum loan by requiring the rent to meet an interest cover ratio, typically 125% to 145% of the mortgage interest, calculated at a stressed rate. In effect, they take the expected rent, divide it by the required ratio, and use the stressed rate to find the loan the rent can support. The higher the rent and the lower the required ratio, the more you can borrow.
A worked example
Suppose a property is expected to rent for £1,500 a month. At a 125% interest cover ratio and a 5.5% stressed rate, this rent could support a loan of roughly £260,000. At a 145% ratio, the same rent supports less, around £225,000. This shows how the rent, the ratio and the stressed rate combine to set your maximum loan, and why higher-rate taxpayers, on a 145% ratio, can usually borrow less.
The loan-to-value cap
Even if the rent supports a large loan, your borrowing is also capped by the maximum loan-to-value, usually around 75%, meaning you need at least a 25% deposit, as our guide to the buy-to-let deposit explains. So your maximum loan is the lower of what the rent supports and what the loan-to-value allows. Both the rent and your deposit therefore shape how much you can borrow.
How a five-year fix can help
Choosing a five-year fixed deal can sometimes let you borrow more, because lenders often apply a lower stressed rate or easier test, given the rate is locked in. For the same rent, this can support a larger loan than a two-year deal. So if you want to maximise borrowing, a longer fix can help, though it ties you in for longer, which is a trade-off to weigh.
Top-slicing and personal income
Some lenders allow top-slicing, using your surplus personal income to support borrowing where the rent alone falls slightly short of the interest cover ratio. This can increase your maximum loan if you have spare income. Not all lenders offer it, and criteria vary, so it is worth asking about, as our guide to buy-to-let mortgages notes. A broker can help find lenders offering top-slicing.
Why your salary matters less
Unlike a residential mortgage, where your salary largely sets how much you can borrow, a buy-to-let depends mainly on the rent. Your income still matters for eligibility and some lenders' criteria, but it is the property's rental potential that usually drives the maximum loan. This is why two people with very different salaries might be able to borrow similar amounts on the same rental property, based on its rent.
Minimum income requirements
While the loan size is driven by rent, many buy-to-let lenders still set a minimum personal income, often a modest threshold, to ensure you can support the property through voids or costs. Some lenders have no minimum income but other criteria. So although your salary does not set the loan amount, it can affect which lenders will consider you, which a broker can help navigate.
Your existing properties
If you already own rental properties, lenders, especially for portfolio landlords, may assess your wider portfolio's finances when deciding how much you can borrow on a new one, as our guide to portfolio landlord mortgages explains. A stretched portfolio can limit further borrowing, while a healthy one can support it. So your existing holdings can influence new buy-to-let borrowing beyond the single property's rent.
Getting the rent assessed
The expected rent used in the calculation is usually confirmed by the lender's valuer, who assesses what the property should achieve, rather than simply your estimate. If the valuer's figure is lower than you hoped, your borrowing could be less than expected. Researching realistic local rents before you buy, and not over-optimistically estimating, helps ensure the rental cover supports the loan you are counting on.
Do not borrow to the maximum
Just because the rent supports a certain loan does not mean you should borrow it all. A smaller loan relative to the rent gives more cash flow buffer for voids, costs and rate rises, making your investment more resilient. Borrowing close to the maximum the rent allows can leave little room if anything goes wrong. Building in headroom, rather than maximising borrowing, is often the wiser approach for landlords.
Bringing the factors together
In practice, your maximum buy-to-let loan is shaped by several factors together: the expected rent, the interest cover ratio for your tax position, the stressed rate, the maximum loan-to-value, any minimum income, your existing portfolio, and whether you choose a longer fix or top-slicing. The lowest of these constraints usually sets your limit. Seeing how they interact helps you understand why your borrowing might be more or less than you first expected.
Get a broker's view
Because lenders' rental cover rules, stress rates and criteria vary so much, a buy-to-let broker can quickly show how much different lenders would lend you on a given property and rent, and identify those most likely to support your purchase, as our guide to how buy-to-let mortgages work notes. This saves time and helps you target realistic properties, rather than discovering late that the borrowing does not reach.
Above all, remember that the rent does the heavy lifting in buy-to-let borrowing, so choosing a property with a strong, realistic rent relative to its price is the single most important step in being able to borrow what you need.
Knowing roughly how much you can borrow before you view properties keeps your search realistic and your offers credible, so it is well worth getting an early indication, from a broker or a buy-to-let calculator, based on sensible rent figures for the area you are targeting.
With realistic rent figures and an early indication of your borrowing, you can house-hunt with confidence and make offers you know the finance will support.
In short
How much you can borrow on a buy-to-let is driven mainly by the expected rent, which must cover the mortgage interest by a ratio of 125% to 145% at a stressed rate, rather than by your salary. Your borrowing is also capped by the maximum loan-to-value of around 75%. A five-year fix can sometimes allow more borrowing, and top-slicing may use personal income to cover a shortfall.
Where to get help and next steps
Read our guides to rental cover and the stress test, the buy-to-let deposit, and buy-to-let mortgages. This is general information, not mortgage, tax or financial advice.