What Is a Buy-to-Let Mortgage?
A buy-to-let (BTL) mortgage is designed for people purchasing a property to rent out rather than live in. These mortgages differ from standard residential mortgages in several important ways, including higher deposit requirements, different affordability assessments, and typically higher interest rates.
The UK buy-to-let market remains a popular investment route, but recent regulatory and tax changes mean it is essential to understand the full financial picture before committing. Our calculator helps you estimate your monthly payments and potential rental yield.
How Buy-to-Let Mortgages Differ from Residential Mortgages
| Feature | Residential Mortgage | Buy-to-Let Mortgage |
|---|---|---|
| Minimum deposit | 5–10% | 25% (typically) |
| Affordability test | Based on income | Based on rental income (ICR) |
| Interest rates | Lower | Higher (typically 0.5–1% more) |
| Mortgage type | Repayment or interest-only | Often interest-only |
| Regulation | FCA regulated | Mostly unregulated (unless consumer BTL) |
| Stamp duty | Standard rates | 3% surcharge on additional properties |
Most BTL mortgages are taken on an interest-only basis, meaning your monthly payments only cover the interest. This keeps costs down and maximises rental cash flow, but you must repay the full capital at the end of the term — usually by selling the property.
Deposit Requirements and LTV
The standard minimum deposit for a buy-to-let mortgage is 25%, giving a 75% LTV. However, your options improve as your deposit increases:
- 75% LTV (25% deposit) — Minimum for most lenders; decent rate selection.
- 65% LTV (35% deposit) — Better rates available from a wider range of lenders.
- 60% LTV (40% deposit) — Access to the most competitive BTL rates.
Use our loan-to-value calculator to determine your LTV and see how it affects available rates.
Interest Coverage Ratio (ICR)
Lenders use the interest coverage ratio to ensure your rental income comfortably covers the mortgage payments. The typical requirement is:
- Rental income must be 125–145% of the monthly mortgage payment.
- This is assessed at a stressed interest rate (commonly 5.5%), not the actual rate you pay.
- For higher-rate taxpayers, some lenders require an ICR of 145% rather than 125%.
Example
If your monthly mortgage payment at the stressed rate is £800, the lender would expect monthly rent of at least £1,000 (at 125% ICR) or £1,160 (at 145% ICR).
Calculating Rental Yield
Rental yield is a key metric for property investors. There are two types:
Gross rental yield:
$$\text{Gross Yield} = \frac{\text{Annual Rent}}{\text{Property Value}} \times 100$$
Net rental yield accounts for costs such as management fees, maintenance, insurance, and void periods. A gross yield of 5–8% is generally considered good in the UK, though this varies significantly by region.
Tax Implications: Section 24 and Beyond
Since April 2020, Section 24 of the Finance Act has fundamentally changed how mortgage interest is treated for buy-to-let landlords:
- You cannot deduct mortgage interest from rental income before calculating tax.
- Instead, you receive a 20% tax credit on your mortgage interest payments.
- This particularly affects higher-rate (40%) and additional-rate (45%) taxpayers, who may now pay significantly more tax on rental income.
Many landlords have responded by purchasing properties through a limited company structure, where mortgage interest remains a fully deductible business expense. Seek professional tax advice before deciding which structure suits you.
Additionally, remember the 3% stamp duty surcharge on purchasing additional properties, and capital gains tax when you eventually sell an investment property.