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Mortgage Stress Test

A lender's calculation checking that a property's rental income will still cover mortgage payments if interest rates rise, typically assessed at 5.5% or higher.

A mortgage stress test is the assessment a BTL lender performs to ensure the property being financed can still service the debt if interest rates rise above their current level.

The stress test rate varies by lender but is typically either 5.5% or the actual product rate plus 2%, whichever is higher. The rental income must cover the monthly interest payment at this stressed rate by the required ICR margin (125% or 145% depending on the borrower's tax position).

The purpose is twofold: to protect the lender from loans that will fail if rates rise, and to protect the borrower from taking on debt they cannot service in adverse conditions.

In practice, the stress test has become a significant constraint on BTL lending in lower-yield areas. With 5-year fixed rates around 5% and stress tests at 5.5-6.5%, properties in southern England with gross yields of 4-5% often cannot achieve 75% LTV because the ICR test fails. Investors either need to put in a larger deposit or choose higher-yielding markets.

Lenders periodically adjust their stress test rates in response to base rate changes and market conditions.

Worked example
A property renting for £700/month. Proposed mortgage at 75% LTV on £120,000. Lender stress rate: 5.5%. Monthly interest at stress rate: £550. ICR = 700/550 = 127%. This passes the 125% threshold for basic rate taxpayers. For a higher-rate taxpayer requiring 145%: 700/550 = 127%. This fails. The investor must reduce the mortgage to approximately £102,000 (65% deposit equivalent) to pass: monthly interest at 5.5% = £467. ICR = 700/467 = 150%. Now passes.
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Referenced in
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