Buy-to-Let Mortgage Affordability Calculator: Rent Cover, LTV & Verdict
Check whether a specific price is affordable: the maximum loan by rent cover, the maximum by 75% loan-to-value, which one binds, the deposit you'd need and the verdict.
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A buy-to-let lender does not ask what you earn -- it asks what the rent covers. That single difference from a residential mortgage is why a landlord on a modest salary can be offered a larger buy-to-let loan than their income alone would ever support on a repayment mortgage, and why a well-paid professional with a low-rent property can be turned down. This calculator runs the two tests a real application faces -- rent cover at a stressed rate, and a loan-to-value ceiling against the price -- on your own numbers, names whichever one limits the loan, and says whether the price is affordable.
Why the test is rent-based, not income-based
The lender's core question is an interest cover ratio (ICR): does the rent cover the mortgage interest, calculated at a higher stressed rate rather than the real pay rate, by a set margin? The Bank of England's own account of the market puts the common minimum at 125% ICR for a basic-rate taxpayer or a limited company, tested at a stress rate of at least the higher of 5.5% or the pay rate plus 2 percentage points. A higher-rate or additional-rate individual keeps less of each pound of rent after tax once Section 24 restricts interest relief to a 20% credit rather than a full deduction, so lenders commonly test them to a tougher 145% ICR in practice (the Bank puts the theoretical break-even nearer 167%, but 145% is what lenders use). None of this looks at your salary directly, beyond a minimum income some lenders require just to approve any application -- typically around £25,000.
The second test: loan-to-value
Rent cover sets a ceiling on the loan; loan-to-value (LTV) sets a separate one. MoneyHelper, the government-backed money-guidance service, puts the common requirement at an LTV of at least 75% -- meaning at least a 25% deposit -- with 80-85% LTV deals existing but hard to secure without an established portfolio. Whichever cap gives the smaller loan is the one that binds: a small deposit against a rent that easily clears the ICR test means the LTV cap limits you; a large deposit against a thin rent means the rent-cover cap does instead. The calculator works out both and names which one is limiting you.
Worked example
£1,200 monthly rent, a £240,000 price, a basic-rate individual buyer, a 5.5% stress rate and 125% cover: the rent alone would support roughly £209,000 of borrowing. But 75% of £240,000 is only £180,000 -- the LTV cap binds first, so the maximum loan is £180,000 and the deposit needed is £60,000. If that is exactly the deposit available, the price is affordable, with rent to spare above the minimum cover required.
Limited company vs individual, and the interest-only default
A limited-company purchase is usually tested at the lower 125% ICR regardless of what an individual owner's tax band would be, because a company deducts mortgage interest in full against Corporation Tax rather than facing Section 24 -- which is why the borrower-type toggle above overrides the tax-status choice. The monthly payment figure defaults to interest-only, the standard structure for a buy-to-let purchase, because the loan itself is still due in full at the end of the term regardless of what the ICR test assumes; switch to capital repayment to see the higher monthly cost over a 25-year term on the same loan instead.
Top-slicing: when your own income can help
If the rent alone falls short of the ICR requirement, some lenders will still lend by using surplus personal income to cover the gap -- a practice called top-slicing. Accord Mortgages, part of Yorkshire Building Society, describes using "surplus personal income (top slicing) to cover a rental shortfall" on its own criteria pages, subject to minimum personal income thresholds (its own figures: £40,000 for an existing landlord, £75,000 for a first-time landlord) and a floor of at least 100% ICR on the rent alone before any top-slicing is added on top. It is not universal across the market and every lender sets its own thresholds, so treat it as a route to ask a broker about rather than a number this calculator assumes.
Before you commit
Once the numbers here look workable, check the full cost of getting to completion on the buy-to-let purchase cost calculator, run a specific loan offer through the pass/fail mortgage stress test, compare the maximum loan against a fuller yield picture on the rental yield calculator, or start from the rent alone with the buy-to-let mortgage calculator.
Interest cover ratio and stress-rate figures: Bank of England Quarterly Bulletin 2023 Q4, "The buy-to-let sector and financial stability", published 15 December 2023, read 13 September 2026 -- describing market practice, not a rate fixed by the regulator. Underwriting-expectation basis: Bank of England / PRA Supervisory Statement 13/16, read live 13 September 2026 (no numeric ICR, stress-rate or LTV figure appears on the statement itself). Loan-to- value figure: MoneyHelper, "Buy-to-let mortgages explained", read 13 September 2026. Top-slicing: Accord Mortgages (Yorkshire Building Society), "Income and top slicing Buy To Let criteria", read 13 September 2026 -- one lender's own published criteria, not a market-wide rule. This is a screening tool built on published conventions, not a mortgage offer, a decision in principle or financial advice -- a broker or lender's own underwriting can differ from every figure here.
Asked constantly
Mainly on the rent, not your salary. The lender tests whether the rent covers the mortgage interest, at a stressed rate rather than the real pay rate, by a set margin -- commonly 125% for a basic-rate individual or a limited company, up to 145% for a higher-rate individual. A separate loan-to-value cap, commonly 75%, applies on top, and whichever produces the smaller loan is the one that actually limits you.
The rent-cover figure is the biggest loan this rent supports at the chosen stress rate and cover ratio. The loan-to-value figure is simply the price multiplied by the lender's maximum LTV (commonly 75%), regardless of the rent. Lenders apply both and use whichever gives the smaller loan -- this calculator shows both and names the one that binds.
Using surplus personal income, on top of the rent, to help clear the rent-cover test when the rent alone falls a little short. Not every lender offers it, and the ones that do set their own minimum personal-income thresholds and usually still require the rent alone to clear a lower floor (Accord Mortgages, for example, requires at least 100% ICR from rent before adding personal income on top) -- ask a broker whether a specific lender's top-slicing criteria would help your case.
Because a company deducts mortgage interest in full against Corporation Tax and is usually tested at the lower 125% cover ratio, while a higher-rate individual can be tested at up to 145% since Section 24 leaves them less of the rent after tax. The extra borrowing comes with company running costs and a different tax position -- see the site's limited company vs personal comparison for that trade-off.
5.5% and pay-rate-plus-2 are both commonly published minimums -- lenders use whichever of the two is higher for a standard variable-rate product, and some price 5-year fixed deals closer to the pay rate itself because the rate is locked for longer. Once a broker or lender has quoted you an actual stress rate for a specific product, enter it under 'Custom / broker-quoted' instead of guessing.
It's the commonly quoted minimum requirement, not a hard ceiling everywhere -- MoneyHelper notes that 80-85% LTV deals exist but are harder to secure unless you already hold an established portfolio. This calculator uses 75% as the standard assumption; treat a higher-LTV offer as the exception rather than something to plan around from the outset.
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Sources
The primary documents this page is built from. Links checked 5 September 2026.
- The buy-to-let sector and financial stability — Bank of England
- SS13/16 Underwriting standards for buy-to-let mortgage contracts — Bank of England / PRA