How buy-to-let lenders assess affordability
Buy-to-let lending is assessed on the property's rent, not your salary. That is why a well-paid borrower can be refused on a property that looks affordable.
Buy-to-let lending works differently from residential lending. The lender is primarily interested in whether the property will cover its own mortgage, and the assessment is built on the rent rather than on the borrower's income. This is why a high earner can be refused a buy-to-let loan that looks modest relative to their salary.
The test is a stress test: the rent must cover the mortgage payment at a rate higher than the one being offered, by a margin. The margin and the stressed rate vary by lender, by product and by the borrower's tax position.
The rental cover test
The standard measure is interest coverage ratio — the rent divided by the mortgage interest — and lenders typically require 125% to 145% at a stressed rate. A higher-rate taxpayer is often required to meet 145%, because the tax treatment of mortgage interest means less of the rent is available to pay it.
- Rent divided by interest at the stressed rate must exceed the required ratio
- Commonly 125% for a basic-rate taxpayer, 145% for a higher-rate taxpayer
- The stressed rate is typically 5.5% or the product rate plus a margin, whichever is higher
- Some lenders also apply a minimum rental figure, particularly on smaller loans
- Fees and any retained element of the rent may be excluded from the calculation
What this means in practice
The cover test caps the loan, and therefore caps the price you can pay for a given rent. If a property lets for £1,000 a month and the lender requires 145% cover at 5.5%, the maximum monthly interest is about £690, which at 5.5% implies a loan of roughly £150,000.
That is the number that decides the deal. If the asking price requires a larger loan than the cover test supports, the deal does not work at that price regardless of how attractive the yield looks on a spreadsheet. Either the price comes down or the deposit goes up.
The other criteria
Beyond the cover test, lenders apply minimum income requirements — commonly £25,000 for a single borrower — and restrict lending on certain property types. New builds, high-rise flats, properties above commercial premises and non-standard construction all attract tighter criteria or refusal.
Portfolio size matters too. A borrower with several properties may be assessed on the whole portfolio's position rather than on the single property, and lenders often cap the number of properties they will lend on. If you are building a portfolio, establish these limits before you commit to a purchase rather than at the application stage.
Common questions
- How much rent do I need to cover a buy-to-let mortgage?
- Lenders typically require the rent to be 125% to 145% of the mortgage interest, calculated at a stressed rate of around 5.5% rather than the rate you are actually paying. A higher-rate taxpayer is usually required to meet the higher figure because of the way mortgage interest is taxed for individuals.
- Do I need a minimum income for a buy-to-let mortgage?
- Usually yes. Most lenders require a minimum income, commonly £25,000, even though the loan is assessed on the property's rent. Some lenders have higher thresholds for portfolio landlords or for particular products. Check the criteria before you make an offer, because failing it at the application stage is expensive.