How does mortgage affordability stress testing work?

Full answer

Mortgage affordability stress testing is a regulatory safeguard designed to prevent borrowers taking on mortgages they could only afford at today's low rates, protecting against payment shock if rates rise during the mortgage term. **Why stress testing exists** Following the 2008 financial crisis, regulators introduced mortgage affordability rules specifically requiring lenders to check that borrowers could withstand a REASONABLE INTEREST RATE RISE, not just afford the mortgage at the specific rate being offered today -- this was designed to prevent a repeat of borrowers being approved for mortgages that were only affordable at historically low rates, then facing serious payment difficulty if rates increased. **How the stress test traditionally worked** The traditional approach required lenders to assess affordability at a rate approximately 1 percentage point above the lender's own reversion rate (the standard variable rate a mortgage would revert to after an initial fixed or discounted period ends) -- so if a lender's SVR was, say, 7%, they would need to check the borrower could afford repayments at around 8%, even if the actual mortgage being offered had a much lower initial fixed rate. **Recent changes giving lenders more flexibility** Regulatory guidance has evolved to give lenders somewhat more flexibility in exactly how they calibrate their stress testing, provided they can still demonstrate a robust approach to protecting borrowers against a plausible future rate rise -- this has allowed some lenders to apply a less mechanical, more risk-based approach to the specific stress rate used, though the underlying principle of testing affordability against a higher hypothetical rate than the actual product rate generally remains. **Why this reduces how much some borrowers can obtain** Because the stress test uses a higher hypothetical rate than the actual mortgage rate, it can significantly reduce the maximum loan amount a lender is willing to offer compared with a simple affordability check based purely on the actual, lower rate being applied for -- a borrower who could comfortably afford repayments at today's actual mortgage rate might still be offered a lower loan amount than expected, because the lender must also confirm they could cope if rates rose to the stressed level. **Fixed-rate mortgages and stress testing** For longer-term fixed-rate mortgages (particularly those fixed for 5 years or more), some lenders apply a less severe stress test (or, in some cases, simply stress test against the actual fixed rate itself rather than a significantly higher hypothetical rate), on the basis that the borrower is protected from short-term rate rises for the whole fixed period -- this can mean choosing a longer fixed-rate deal sometimes allows a borrower to access a larger mortgage than an equivalent shorter fixed or variable rate deal would permit, purely because of how the stress test is applied. **Worked example** A borrower applies for a mortgage with a 2-year fixed rate of 4.5%, but the lender's standard variable rate that the mortgage would revert to afterwards is 7.5%. Under a traditional stress test approach, the lender would check the borrower's affordability at around 8.5% (roughly 1 percentage point above the 7.5% reversion rate), even though they are actually only committing to pay 4.5% for the first 2 years -- if the borrower's income and expenditure would make an 8.5% rate genuinely unaffordable, the lender may offer a smaller loan amount than the borrower expected, based purely on their current, comfortable ability to afford the actual 4.5% rate. **Practical tip** When mortgage shopping, ask different lenders how they specifically apply affordability stress testing (since approaches can genuinely differ following recent regulatory flexibility), and consider that a longer fixed-rate deal might, in some cases, allow access to a larger mortgage than a shorter fixed or variable rate product, purely due to differences in how the stress test is calculated.

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