Answers · UK 2025/26

How does a buy-to-let mortgage differ from a residential mortgage?

Buy-to-let mortgages are assessed primarily on the property's expected rental income (typically needing to cover 125-145% of the mortgage payment) rather than your personal salary, usually require a larger deposit (often 20-25% minimum), and are more commonly interest-only. Interest rates and arrangement fees also tend to be higher than equivalent residential mortgages.

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Buy-to-let mortgages are a distinct product category from residential mortgages, reflecting the different risk profile and purpose of a property bought to let out rather than to live in. **Affordability based on rental income, not just salary** While residential mortgages are assessed primarily against your personal income and outgoings, buy-to-let lenders focus mainly on the property's expected rental income, requiring it to cover a set percentage (commonly 125% to 145%, sometimes higher for higher-rate taxpayers) of the mortgage payment, calculated using a stress-tested notional interest rate rather than the actual pay rate -- this is designed to ensure the rental income provides a comfortable buffer even if interest rates rise or there are void periods. **Larger deposit requirements** Buy-to-let mortgages typically require a minimum deposit of 20-25% (75-80% maximum loan-to-value), noticeably higher than the 5-10% minimum sometimes available on residential mortgages, reflecting the higher risk lenders associate with rental properties. **Interest-only is common** Many buy-to-let mortgages are taken on an interest-only basis (paying only the interest each month, with the capital repaid at the end of the term, typically from selling the property or refinancing), unlike residential mortgages where full repayment mortgages are the norm -- this reduces monthly costs for the landlord but requires a clear repayment strategy for the capital. **Higher rates and fees** Buy-to-let mortgage interest rates and arrangement fees are typically somewhat higher than equivalent residential products, reflecting the additional risk lenders take on with rental properties, particularly around tenant-related income uncertainty. **You usually need to already own a home** Many buy-to-let lenders require you to already be a homeowner (either mortgaged or outright) before approving a buy-to-let mortgage, since this is treated as evidence of financial stability and experience -- though "consumer buy-to-let" or first-time landlord products do exist for those without this history, often with additional conditions. **Using a buy-to-let mortgage as your own home is not allowed** It is a breach of mortgage terms (and potentially mortgage fraud) to live in a property financed with a buy-to-let mortgage yourself -- lenders require the property to be genuinely let to tenants, and using it as your own residence without switching to an appropriate residential mortgage can have serious consequences. **Worked example** A lender requires rental income to cover 145% of the mortgage payment at a stressed rate of 6.5%. On a £180,000 interest-only buy-to-let mortgage, the stressed monthly interest is £975; the required minimum rental income is £975 × 1.45 = £1,413.75 a month, regardless of what the landlord's actual pay rate or personal income might otherwise support. **Practical tip** Get a realistic rental valuation from a local letting agent before applying for a buy-to-let mortgage, since the rental income (not your personal salary) is usually the primary factor determining how much you can borrow -- an overly optimistic rental estimate can lead to a declined application or a lower maximum loan than expected.