Buy-to-Let Mortgage Stress Test Calculator
BTL stress test.
Stress test a buy-to-let mortgage against typical lender DSCR requirements — see if rents cover interest at stressed rate scenarios.
What this tool does
This tool calculates whether a buy-to-let property generates enough rental income to meet lender affordability requirements under stress conditions. It models your scenario by applying a higher stress rate to your mortgage, then determines the monthly rent needed to cover that stressed interest cost multiplied by your lender's debt service coverage ratio (DSCR). The result shows the rental income threshold your property must achieve. The stress rate—typically set above your actual mortgage rate—reflects how lenders test resilience to future rate rises. Key inputs driving the outcome are your loan amount, the stress rate applied, and the DSCR multiplier. A typical use case is evaluating whether a property's expected rent can satisfy lender criteria before submitting an application. Note that this calculation illustrates rental income requirements only and does not account for operating costs, tax implications, or other expenses.
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Formula Used
Spotted something off?
Calculations or display — let us know.
Disclaimer
Results are estimates for educational purposes only. They do not constitute financial advice. Consult a qualified professional before making financial decisions.
BTL mortgage stress test calculator checks if rental income covers stressed interest at lender DSCR (typically 1.25-1.45x). lenders apply stress rate (often 5.5%+) regardless of actual product rate. 200k loan at 5.5% stress = 917/month interest. With 1.25 DSCR: required monthly rent = 1,146. Below this: mortgage rejected.
Example: 400k property, 100k deposit, 300k loan. Stress rate 5.5% = 1,375/month interest. 1.25 DSCR = 1,719 required monthly rent. 1.45 DSCR (limited company) = 1,994. Property rent 1,800: passes individual (1.25), fails limited company (1.45). Important to know which DSCR your lender uses.
BTL stress test rules: the relevant financial regulator (Prudential Regulation Authority) requires 1.25x at 5.5% stress (or 5-year fix if rate higher). Limited company SPVs typically need 1.45x. Higher LTV (75-80%): stricter requirements. New requirements for portfolio landlords (4+ properties): full portfolio stress test. Many BTL applications fail stress test - have alternative funding plan or accept lower LTV.
Quick example
With property price of 400,000 and deposit of 100,000 (plus actual mortgage rate of 5% and stress rate of 5.5%), the result is PASSES. Change any figure and watch the output shift — it's often more useful to see the pattern than to memorise the formula.
Which inputs matter most
You enter Property Price, Deposit, Actual Mortgage Rate %, Stress Rate %, and Expected Monthly Rent. Not every input has equal weight. Adjusting one input at a time toward extreme values shows which ones move the result most.
What's happening under the hood
Stress monthly interest = loan × stress rate / 12. Required rent = stress interest × DSCR. The formula is listed in full below. If the number looks off, you can retrace the calculation by hand — that's the point of showing the working.
Why run this
Running the numbers makes the trade-offs concrete. Small changes in the inputs can move the result more than intuition suggests, which is hard to judge without working it out.
What this doesn't capture
This is a simplified model that holds its assumptions constant. Real outcomes vary with market conditions, costs, taxes, and timing, so the figure is best read as one scenario rather than a forecast.
£400,000-£100,000=loan, 5.5% stress × 1.25 DSCR vs £1,800 = PASSES.
Inputs
This example uses typical values for illustration. Adjust the inputs above to match a specific situation and see how the result changes.
Sources & Methodology
Methodology
This calculator models a buy-to-let mortgage stress test by computing the rental income required to meet lender affordability criteria. It first calculates the loan amount by subtracting the deposit from the property price. The monthly stress interest is then derived by applying the stress rate (expressed as an annual percentage) to the loan amount and dividing by 12. The required monthly rent is determined by multiplying this stress interest by the lender's debt service coverage ratio multiplier, which represents the income multiple lenders typically require to approve the mortgage. The calculator assumes a constant stress rate applied uniformly throughout the loan term and does not account for fees, taxes, maintenance costs, vacancy periods, capital appreciation, or changing interest rates beyond the stress scenario modelled.
Frequently Asked Questions
Why stress test exists?
Individual vs Limited Company DSCR?
Failing stress test - options?
Portfolio landlord requirements?
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