Buy-to-Let Mortgage Stress Test Calculator: Rent Cover, ICR & Max Loan
Rent cover at the stress rate, 125% or 145% ICR, the maximum loan the rent supports and the LTV — the test lenders run before a decision in principle.
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Buy-to-let lenders do not lend on your salary; they lend on the rent. The test is an interest cover ratio: the rent has to cover the mortgage interest — calculated at a stressed rate, not the pay rate — by a margin. This calculator applies the mechanics lenders publish: the stress rate (commonly the higher of 5.5% and the pay rate plus 2%), the rent-cover requirement (125% for basic-rate taxpayers and limited companies, up to 145% for higher-rate taxpayers, because Section 24 leaves them less of the rent), and the loan-to-value cap most lenders set at 75%.
Why higher-rate taxpayers get a tougher test
Since mortgage interest stopped being deductible for individual landlords, a higher-rate taxpayer keeps less of every pound of rent after tax. Lenders price that in with a higher cover ratio. The same landlord buying through a company is usually tested at 125% — one of the reasons the company-versus-personal question comes up at the mortgage stage.
Reading the result
- Rent cover achieved is rent divided by stressed monthly interest. Below the requirement, the lender reduces the loan.
- Maximum loan is the largest mortgage this rent supports at the chosen cover ratio and stress rate — the number that decides your deposit.
- Five-year fixes are often stressed at the pay rate rather than 5.5%, which is why they can support a larger loan; ask the broker.
Before the application
Check the yield on the asking price, the stamp duty with the surcharge, and what the rent means for your tax with the rental income tax calculator. If the rent you need to pass the test is above what the local market pays, the affordability calculator shows what tenants there can reference.
Stress rates, cover ratios and LTV caps are lender criteria that change with the market and by product; the defaults here are the commonly published ones, not a rule. This is a screening tool, not a decision in principle. General information, not advice.
Asked constantly
The lender recalculates your mortgage interest at a higher 'stress' rate — commonly 5.5% or the pay rate plus 2% — and requires the rent to cover that interest by 125% to 145%. If it does not, the loan is cut until it does.
Rent × 12 ÷ (stress rate × cover ratio). At £1,200 rent, 5.5% and 145% that is about £180,000; at 125% about £209,000. Most lenders also cap the loan at 75% of the price.
Because companies deduct interest in full and are usually tested at 125% cover, while a higher-rate individual is tested at up to 145%. The extra borrowing comes with company costs and a different tax position — run both.
Some require a minimum personal income (often £25,000) and most credit-check you, but the loan size is driven by the rent cover test, not an income multiple.
Doing this every quarter, not just once?
Keep the same figures all year instead of re-typing them: rent and expenses per property, the Section 24 finance costs and the MTD quarterly totals, in one workbook.
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Disclosure: we make and sell the Tax Pack — this is our own product, not a paid recommendation. It does not file anything with HMRC and it is not tax advice; filing goes through you, your accountant or software on HMRC’s compatible-software list.
Sources
The primary documents this page is built from. Links checked 5 September 2026.
- SS13/16 Underwriting standards for buy-to-let mortgage contracts — Bank of England / PRA
- Tax relief for residential landlords: how it's worked out (with case studies) — GOV.UK / HMRC