Mortgages
Enquire Now
Mortgages
Enquire Now
  • Buy-to-Let Mortgages

Buy-to-Let Mortgage Guide.

Rental yields, stress tests, tax, and licensing — everything a landlord needs to know.

Buy-to-let investment can generate both rental income and long-term capital appreciation, but lenders, regulators, and HMRC all treat it differently from residential ownership. This guide covers how buy-to-let mortgages work, how lenders assess affordability, the tax landscape post-2017 reforms, and what experienced landlords consider before adding to a portfolio.

Guide

1

How buy-to-let mortgages differ

Buy-to-let (BTL) mortgages are assessed primarily on the rental income the property is expected to generate, not your personal income. Lenders apply a rental coverage ratio — typically 125–145% of the monthly mortgage interest payment at a stressed rate — to ensure the rent covers costs with a safety margin.

Most BTL mortgages are interest-only, meaning monthly payments cover only the interest and the capital balance remains constant. This keeps monthly outgoings low and maximises cash flow, but the full loan must be repaid at the end of the term — usually through a sale or remortgage.
Deposits for BTL properties are typically a minimum of 25%, though some lenders accept 20%. Lower deposits carry higher rates and stricter rental coverage requirements. Portfolio landlords (those owning four or more mortgaged properties) face additional underwriting criteria including a full portfolio review.

2

Rental coverage and stress testing

Lenders do not simply check that the rent covers the current mortgage payment. They stress test at a notional rate — often 5.5–6% regardless of the actual rate — to ensure the property remains viable if rates rise. This is the rental stress test, and it often catches landlords who assume any positive monthly cash flow is sufficient.

For higher or additional rate taxpayers, most lenders apply a 145% coverage ratio at the stressed rate. For basic rate taxpayers, this may reduce to 125%. The practical implication is that higher earners often need a larger deposit or lower loan to achieve the same borrowing.

3

Tax: Section 24 and its implications

The Section 24 mortgage interest relief restriction, fully phased in since 2020, means individual landlords can no longer deduct mortgage interest as a business expense. Instead, you receive a basic rate (20%) tax credit on the lower of your finance costs, rental profits, or total income. For higher and additional rate taxpayers, this significantly increases the effective tax rate on rental income.

Holding BTL property within a limited company preserves full mortgage interest deductibility against rental profits, and corporation tax rates (currently 25% for profits above £250,000) are typically lower than higher-rate income tax. However, extracting profits from a company via salary or dividends creates additional tax complexity. Professional tax advice is essential before choosing a structure.

4

Stamp Duty surcharge and other costs

Purchases of additional residential properties attract a 3% SDLT surcharge on top of standard rates. On a £300,000 property, this adds £9,000 in stamp duty compared to a residential purchase. The surcharge applies to any purchase where the buyer owns another residential property at completion — not just to declared investment purchases.

Other costs to factor into your yield calculation include: letting agent fees (typically 8–15% of rent), maintenance and repairs, buildings insurance, void periods, ground rent and service charges on leasehold properties, and accountancy fees if using a company structure.

5

Licensing and regulation

Houses in Multiple Occupation (HMOs) — where three or more unrelated tenants share facilities — require a mandatory HMO licence from the local authority if the property has five or more occupants. Many councils have also introduced selective or additional licensing schemes covering all private rented properties in defined areas, regardless of size.

Failure to license an HMO can result in an unlimited fine and a Rent Repayment Order requiring you to repay up to 12 months’ rent. Prospective landlords should always check licensing requirements with the relevant local authority before completing a purchase.

6

Assessing rental yield

Gross rental yield is calculated as annual rent divided by property value, expressed as a percentage. A gross yield of 5–7% is broadly considered viable in most UK markets, though you must account for the costs above to arrive at net yield. In London and the South East, yields are often lower (3–4%) but historically stronger capital growth has compensated.

Net yield, after costs, is the figure that truly determines cash flow viability. Model it conservatively — assume 10% void allowance, maintenance at 1% of property value annually, and management fees — before committing to a purchase.
  • Key Takeaways

What to remember from this guide.

  • BTL mortgages are assessed on rental income, not personal earnings — rental coverage ratios apply
  • Section 24 has fundamentally changed the tax position for higher-rate individual landlords
  • A limited company structure preserves interest deductibility but adds complexity — take tax advice
  • The 3% SDLT surcharge applies to all additional residential property purchases
  • Always check local HMO and selective licensing requirements before exchanging contracts