How buy to let mortgages work in the UK

Buy to let mortgages differ from residential mortgages in three fundamental ways - how affordability is assessed, how the interest rate is calculated, and the tax treatment of the mortgage cost. Understanding these differences is essential before choosing a lender and product.

Rental income stress testing

Most buy to let mortgage lenders require the monthly rental income to cover the mortgage payment by 125% to 145% at a stressed interest rate (typically 5% to 5.5% regardless of the actual product rate). This stress test is designed to ensure the property remains financeable if interest rates rise. Higher rate taxpayers are typically subject to a higher stress test than basic rate taxpayers. Understanding which stress test each lender applies is essential for maximizing the loan amount available.

Bank of England held base rate at 4.25% in June 2026 - waiting for inflation to cool.

73% of UK SMEs expect to grow in the next 12 months - confidence remains strong.

Personal name versus limited company BTL

Following the phasing out of mortgage interest tax relief for individual landlords, many investors now purchase buy to let properties through limited companies or SPVs. The tax treatment of mortgage interest as a business expense within a company significantly improves net returns for higher and additional rate taxpayers. Most specialist BTL lenders now offer limited company products, though rates are typically slightly higher than personal name equivalents.

Portfolio landlord rules (PRA)

Since 2017, landlords with 4 or more mortgaged properties are classified as portfolio landlords under PRA underwriting rules. Portfolio landlords must provide details of their entire portfolio when applying for any new or remortgage, and lenders must assess the whole portfolio rather than the individual property. This makes portfolio landlord applications more complex and requires a specialist broker to identify the right lender. Money Pilot compares specialist portfolio finance and buy to let mortgages at zero broker fees.

Buy to let mortgages - four scenarios where a specialist broker makes the difference

These four common landlord situations illustrate why specialist broker access to the full BTL lender market delivers significantly better outcomes than approaching a single lender directly.

Fee-free comparison vs specialist structuring - why choose?

The BTL market splits into fee-free generalists comparing mainstream rates and specialist brokers handling limited company, HMO and portfolio complexity - usually for a fee. Money Pilot is built to be both at once: whole-of-market comparison, specialist structuring, zero broker fees.

Personal name or limited company - the decision, not the criteria

The criteria are on this page; the decision is maths. Personal ownership: simpler, slightly cheaper rates, but mortgage interest relief is restricted to a 20% credit - expensive for higher-rate taxpayers. Limited company: full interest deduction against corporation tax and the friendlier stress test, but marginally higher rates, accountancy costs, and dividend tax when profits come out.

The break-even in practice: higher-rate taxpayers building a portfolio almost always model better in a company; basic-rate taxpayers holding one or two properties often model better personally. The honest answer needs your numbers - we run both routes side by side, with your accountant where you have one, before any application is made. Structure first, rate second: the structure decision is worth more than any 0.1% of rate.

Go deeper

Start with our guides to the buy to let stress test UK, limited company buy to let UK and portfolio landlord rules UK.