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If you’re investing in property and considering a buy-to-let mortgage, one of the most important things to understand is how lenders assess affordability — and it’s very different from a standard residential mortgage.
The key term you’ll come across is the Interest Coverage Ratio (ICR), often tested through what’s known as the Interest Coverage Ratio Test (ICRT). These calculations determine how much you can borrow based on the expected rental income from your investment property.
Let’s break it down.
🔢 What is Interest Coverage Ratio (ICR)?
ICR is a calculation used by lenders to make sure the rental income from your property is enough to cover the mortgage payments, with a cushion.
Most lenders want to see the rent cover the mortgage interest by 125% to 145%, depending on your tax status and the type of borrower you are.
📊 What is the ICR Test (ICRT)?
The ICRT (Interest Coverage Ratio Test) is the formal name for the stress test lenders apply to your projected rental income. It involves three key elements:
- Stress Rate: A notional interest rate (often higher than your actual rate) used to stress-test affordability. This is typically 5.5%, though it can vary.
- ICR Band: This is usually 125% for limited companies, or 145% for higher-rate taxpayers personally.
- Loan Interest Only: The test is calculated on an interest-only basis, even if you plan to repay capital.
🧮 How is It Calculated?
Here’s the formula most lenders use:
Max Loan = (Monthly Rent x 12) / (Stress Rate x ICR)
📌 Example:
- Monthly Rent: £1,200
- ICR: 145% (1.45)
- Stress Rate: 5.5%
Max Loan = (£1,200 x 12) / (5.5% x 1.45)
= £14,400 / 0.07975
= £180,451
In this case, the maximum loan available would be around £180,000.
🏢 Limited Company vs Personal BTL
- Limited Company BTL: Usually tested at 125% ICR, which means you can often borrow more.
- Personal BTL (basic-rate taxpayer): Often 125% ICR.
- Personal BTL (higher-rate taxpayer): Typically 145% ICR or higher.
This is one reason why many investors now use limited companies to grow their portfolios.
📈 Do Fixed Rates Change the Calculation?
Yes — some lenders apply a lower stress rate if you choose a 5-year fixed rate, which can significantly increase your borrowing potential. For example:
- Stress rate may drop to 4.5% or even 4.0%
- Some lenders may also apply top slicing (using surplus income) for further flexibility
🧾 Other Factors Lenders Consider
While ICRT is the foundation, lenders also look at:
- Property type (e.g. flats, HMOs, new builds)
- Portfolio size and experience
- Credit history
- Loan-to-Value (LTV)
- Your personal or company tax position
💬 Final Thoughts
Understanding ICRT is essential for anyone entering or expanding in the buy-to-let market. It’s not just about finding a property and securing a rate — it’s about making sure the rental income stacks up under lender scrutiny.
Whether you’re a first-time landlord or expanding a portfolio, speaking to a broker who understands the nuances of buy-to-let lending and ICR rules is key.
📞 Need help navigating the numbers?
We work with specialist lenders and understand how to structure cases — even with complex tax positions, portfolios, or adverse credit.
Let’s chat – your next investment could be closer than you think.