Understanding ICR: How Lenders Calculate Buy-to-Let Mortgage Affordability

Every buy-to-let mortgage application comes down to one question: does the rent cover the debt? The number lenders use to answer that question is the Interest Cover Ratio. Get your head around it and you will know exactly what any lender will think of a deal before you apply.

What ICR Actually Means

ICR stands for Interest Cover Ratio. It measures how many times over the rental income covers the mortgage interest.

The formula is:

ICR = (Annual rental income ÷ Annual mortgage interest) × 100

An ICR of 100% means the rent exactly covers the interest. An ICR of 125% means the rent is 25% above the interest. Lenders set minimum thresholds that a property must clear before they will approve the mortgage. Fall short and the application fails, even if you can comfortably afford the payments from your other income.

This is a rental property test, not a personal affordability test. A landlord earning £100,000 a year from their day job will still be declined if the property itself does not generate sufficient rental income relative to the mortgage.

Why Lenders Use a Stress Rate, Not the Actual Rate

Here is where most landlords are caught out. Lenders do not calculate ICR using the actual mortgage rate you will be charged. They use a higher hypothetical rate called the stress rate.

The stress rate builds in a buffer. Lenders are testing whether the property could still service its debt if rates rise significantly. In 2026, most UK lenders apply a stress rate of 5.5%, regardless of whether the actual product rate is lower.

That means if you are fixing at 4.2%, the ICR calculation runs at 5.5% regardless. The gap between what you will actually pay and what the lender tests you at can make a real difference to whether a deal works.

Some lenders use a lower stress rate. Products fixed for five years or more may attract 5.0% or even the pay rate in certain cases. Criteria vary by lender and product type, which is why the same property can pass with one lender and fail with another.

The Three ICR Thresholds

ICR requirements differ depending on your tax status, because tax directly affects how much of the rental income you will actually keep after HMRC takes its share.

Borrower type	Standard ICR requirement
Basic-rate taxpayer (personal name)	125%
Higher-rate taxpayer (personal name)	145%
Additional-rate taxpayer (personal name)	~167%
Limited company (SPV)	125%

The difference reflects Section 24 of the Finance (No. 2) Act 2015. Personal-name landlords can no longer deduct mortgage interest as a property expense. Instead, they receive a 20% basic-rate tax credit on that interest. For basic-rate taxpayers the net effect is roughly equivalent to the old system. For higher and additional-rate taxpayers, who pay 40% or 45% on rental income but only receive a 20% credit, the tax drag is significant.

Lenders know this. A higher-rate taxpayer has less cash left after tax from the same rental income, so lenders require a bigger rental cushion before they will lend.

Limited company borrowers are treated the same as basic-rate taxpayers at 125%, because corporation tax is flat at 25% and mortgage interest remains fully deductible for companies. The lending maths is more predictable.

The 167% threshold for additional-rate taxpayers is the theoretical maximum. In practice, many lenders cap their ICR assessment at 145% for all personal-name borrowers, regardless of tax band. Check with a broker for each lender's specific position.

A Worked Example: £200,000 Loan

Take a property with a £200,000 interest-only mortgage. The lender offers a rate of 4.3%, but stress tests at 5.5%.

Annual interest at the stress rate: £200,000 × 5.5% = £11,000 per year

Minimum rent required by taxpayer status:

Taxpayer status	ICR	Annual rent needed	Monthly rent needed
Basic rate / Ltd Co (125%)	1.25 × £11,000	£13,750	£1,146
Higher rate (145%)	1.45 × £11,000	£15,950	£1,329
Additional rate (167%)	1.67 × £11,000	£18,370	£1,531

On the same loan, at the same rate, a higher-rate taxpayer needs £183 per month more in rent than a basic-rate taxpayer or a limited company. That is not a marginal difference. In many UK markets it can be the gap between a viable investment and one that cannot be funded.

For a limited company borrower, the lower ICR threshold means access to a meaningfully wider range of properties at the same loan size.

What Gross Yield Do You Actually Need?

If you want to know whether a property is likely to pass ICR before you get into the detail, gross yield gives you a quick steer.

At 75% LTV with a 5.5% stress rate:

ICR requirement	Minimum gross yield at 75% LTV
125% (basic rate / Ltd Co)	~5.2%
145% (higher rate)	~6.0%
167% (additional rate)	~6.9%

Move to 70% LTV and the numbers become more forgiving:

ICR requirement	Minimum gross yield at 70% LTV
125%	~4.8%
145%	~5.6%
167%	~6.4%

These are approximations, and lenders will use the actual rent rather than a yield calculation, but they are useful for a quick sense-check when assessing a deal. A higher-rate taxpayer looking at properties yielding 5.5% at 75% LTV will face a difficult time with most standard lenders.

What Moves Your ICR

Understanding the variables helps you structure deals that work.

Loan amount. A smaller loan means less stressed interest to cover. Moving from 75% to 70% LTV on a £200,000 property reduces the loan by £10,000. At 5.5%, that saves £550 in annual interest, which can tip a borderline case into a pass.

Stress rate. Not all lenders use 5.5%. A specialist lender using 5.0%, or a product qualifying for pay-rate assessment, can change the ICR calculation significantly. A broker who knows the market is useful here.

Tax status. If you are a higher-rate taxpayer in personal name, borrowing through a limited company reduces the required ICR from 145% to 125%. On a £200,000 loan, that is £183 per month less rent required.

Rental income. Higher rent is the most direct improvement. If the property is let below market rate, adjusting it before applying helps. A valuer's rental assessment based on comparable local evidence can also support the application if the property is void.

Portfolio Landlords: ICR Expands Across the Whole Portfolio

Cross four mortgaged properties and the ICR calculation changes in a significant way. The Prudential Regulation Authority's Supervisory Statement SS13/16, updated in January 2026, sets out what lenders must do when dealing with portfolio landlords.

At four or more mortgaged buy-to-let properties, most lenders assess ICR at portfolio level. Every property you hold is included, not just the one you are applying to finance. One underperforming property in the background can affect your ability to secure a mortgage on an otherwise strong new acquisition.

This does not make growth impossible. It does mean you need to track your portfolio ICR proactively and approach lenders that specialise in portfolio applications. The documentation requirements also increase: a portfolio schedule, rental income evidence across all properties, and sometimes a brief business plan.

The January 2026 SS13/16 update reaffirmed the core standards, with full implementation effective from January 2027. Most specialist lenders are already applying the updated criteria.

If a Deal Fails ICR

There are practical routes if a property falls short:

• Reduce the loan. A smaller mortgage directly reduces the interest to cover. Even a modest deposit increase can tip the balance.
• Try a specialist lender. Stress rates and ICR thresholds vary. What fails with a high-street lender may pass with a specialist.
• Borrow through a limited company. The 125% threshold and often more favourable stress rate treatment can unlock deals that do not work in a personal name.
• Improve the rent. Get a current market rent assessment from a local agent if the property is below comparable rents.
• Use a specialist broker. They know which lenders suit which deal types, and can save unnecessary credit file searches.

ICR is not the whole mortgage picture. Lenders also check personal income, credit history, and property condition. But it is the central affordability calculation for every buy-to-let application. Know your number before you apply.

This article is for informational purposes only and does not constitute financial or investment advice. Tax rules and legislation change frequently. Always verify current rates with HMRC or GOV.UK and seek independent professional advice before making investment decisions.