What your result means
A residential second home mortgage is assessed largely like a normal residential mortgage: the lender applies an income multiple, commonly 4 to 4.5 times your income, after taking into account any existing mortgage commitments, and runs a full affordability check behind that headline number. That is why this calculator shows a range rather than a single figure. A buy-to-let works differently. Since the mortgage is meant to be serviced by the property's own rent rather than your salary, the lender instead asks whether the rent covers a stressed interest cost by a set margin, the interest coverage ratio (ICR), using a notional stress rate rather than your actual pay rate.
For buy-to-let, the maximum loan the rent supports is compared against the maximum loan your deposit allows at a typical 75% loan-to-value ceiling, and the smaller of the two is your limit. Once you have a price range, our running cost calculator and stamp duty calculator can help you check the full picture, and our guide to buying a second home covers the wider process.
Worked example
A basic-rate taxpayer buying a second home near Bath as a residential purchase earns £70,000 a year and pays £1,200 a month on their existing mortgage. Deducting £14,400 a year of mortgage payments leaves £55,600 of income for the multiple test; at 4x to 4.5x, that supports a loan of roughly £222,400 to £250,200. Added to a £60,000 deposit, the indicative price range is about £282,400 to £310,200. The same buyer considering a buy-to-let flat in Bristol instead, expecting £1,400 a month in rent, is assessed quite differently: at a 125% ICR and a 5.5% stress rate, the rent supports a maximum loan of about £244,000, but a £75,000 deposit at the typical 75% maximum loan-to-value caps the purchase nearer £300,000, so the deposit, not the rent, is the binding limit in this case.
How this is calculated
| Buy-to-let taxpayer band | ICR required |
|---|---|
| Basic rate, or limited company | 125% |
| Higher or additional rate | 145% |
The ICR and stress-testing requirement comes from the Prudential Regulation Authority's Supervisory Statement SS13/16, which sets underwriting expectations for buy-to-let lenders. The exact stress rate is lender-set, not a single number fixed by the regulator; 5.5%, or the pay rate plus 2 percentage points if higher, is common market practice. A 5-year or longer fixed-rate product is often stress-tested less harshly. The 4x to 4.5x residential income multiple and the 75% buy-to-let loan-to-value ceiling are typical current lender practice, not statutory limits, and vary between lenders and by borrower profile. Sources: Bank of England PRA SS13/16, FCA Handbook MCOB 11.9.
What this calculator does not cover
It does not run a full residential affordability stress test, which also looks at your outgoings, dependants and future rate rises, not just an income multiple. It does not calculate stamp duty on the additional-property surcharge (see our stamp duty calculator), arrangement fees, or the impact of Section 24 mortgage interest restriction on a buy-to-let's actual after-tax return. It assumes one existing mortgage; it does not model a portfolio landlord's aggregated exposure across several properties, which many lenders assess with tighter rules.
Questions
Why does buy-to-let borrowing not use my salary?
A buy-to-let mortgage is expected to be paid from the property's own rental income, so lenders size it around whether the rent covers a stressed interest cost, not around your personal income multiple, though most lenders still require a minimum personal income to qualify at all.
Why is the interest coverage ratio higher for higher-rate taxpayers?
Since mortgage interest relief for individual landlords is now given as a basic-rate tax credit rather than a full deduction, a higher-rate taxpayer keeps less of their rental income after tax, so lenders require more rental cover to compensate.
Is 4.5x the most I can borrow for a residential second home?
No single multiple applies everywhere. 4 to 4.5x is typical, but some lenders offer higher multiples to higher earners or professionals, and all lenders also run a fuller affordability check behind the headline multiple.
What loan-to-value can I get on a buy-to-let?
75% is a common market ceiling, though some lenders go to 80% at a rate or fee premium. This calculator uses 75% as the default assumption.
Does this calculator include stamp duty?
No. Use the separate stamp duty calculator to estimate the additional-property surcharge on top of the purchase price shown here.
Last reviewed 15 September 2026 against Bank of England PRA and FCA published rules. Next review April 2027.
This calculator gives a general estimate from the figures you enter. It is not financial, tax, legal or mortgage advice. Rules change and personal circumstances matter, so confirm with a qualified professional before you act. See the full disclaimer.