The buy-to-let stress test explained
Buy-to-let lenders size your loan from the rent, not your salary. They require the rent to cover the mortgage interest by a margin — the interest coverage ratio, usually 125% for basic-rate and 145% for higher-rate taxpayers — tested at a stressed interest rate.
What the stress test does
Rather than lending a multiple of your income, a BTL lender checks that the property’s rent comfortably covers the mortgage interest, even if rates rise. It applies an interest coverage ratio (ICR) at an assumed ‘stress’ interest rate, and the loan is capped at the level the rent can support.
The numbers
- ICR 125% — common for basic-rate taxpayers and limited companies.
- ICR 145% — common for higher-rate taxpayers.
- Stress rate — an assumed rate (often higher than the pay rate) the rent is tested against.
- Max loan = annual rent ÷ (ICR × stress rate).
Worked example
What £1,200 rent supports
ICR (higher-rate): 145%
Stress rate: 5.5%
Max loan = 14,400 ÷ (1.45 × 0.055): ≈ £180,564
At a 125% ICR the same rent supports more — roughly £209,000. The calculator below lets you test your own figures.
How to improve the outcome
- Higher rent or a lower stress rate increases the loan.
- Basic-rate / company cases (125%) borrow more than higher-rate (145%) per pound of rent.
- A larger deposit reduces the loan needed to pass.
- Holding property in a company can change the ICR applied — see SPV buy-to-let.
Where the test catches people out
The rent used is the surveyor's assessment of market rent, not the figure you hope to achieve or even the rent a tenant has agreed. If the surveyor comes in below your expectation, the maximum loan falls with it — and that happens after you have committed to the purchase.
The second trap is the stress rate. Lenders test at a rate above the one you will pay, and some apply a lower stress rate to five-year fixed products than to shorter ones. That single criterion difference can change your maximum loan materially, which is why the product choice and the borrowing figure are not independent decisions.
What to do when the numbers fall short
Three levers, in rough order of practicality. More deposit reduces the loan the rent has to cover, and is usually the fastest fix. A different lender may apply a gentler coverage ratio or stress rate — limited company products often do. Or a different property, since the constraint is the rent relative to the price rather than anything about you.
What does not help is arguing about your personal income, because on a buy-to-let it is a threshold rather than a multiplier. Model the effect of each lever on the stress test calculator before deciding which to pull.
Buy-to-let, answered
Why is the stress rate higher than my actual rate?+
Lenders test affordability against a higher assumed rate so the rent still covers the mortgage if interest rates rise. It’s a buffer, not the rate you’ll pay.
Does a limited company get a better stress test?+
Often the ICR is lower (around 125%) for limited company and basic-rate cases than the 145% applied to higher-rate individuals, which can mean a larger loan for the same rent.
What if my rent doesn’t pass?+
Options include a larger deposit (smaller loan), a lower-rate product, a different lender, or top-slicing where a lender uses surplus personal income. We’ll find the route that works.
Why does my lender use a higher rate than I am paying?+
Because it is testing whether the rent would still cover the mortgage if rates rose during your ownership, rather than only today. The stressed rate is a resilience check, not a prediction. Some lenders apply a lower stress rate to five-year fixes, on the basis that the payment cannot move during that period.