Buy-to-let mortgage calculator: rent, ICR, and stress testing
Estimate the rent required for a proposed buy-to-let loan, the maximum loan supported by rent, loan-to-value, interest-only cost, and gross yield.
Property and rental figures
Use the stress rate and ICR supplied by the lender or broker when available.
Illustrative result
Rental-stress estimate for an interest-only buy-to-let mortgage.
Rent covers this stress illustration
Required rent: £1,074 a month
- Mortgage required
- £187,500
- Loan to value
- 75.0%
- Actual stress coverage
- 163%
- Rent-supported loan
- £244,364
- Monthly interest at pay rate
- £820
- Gross rental yield
- 6.72%
Rent minus mortgage interest only
£580 per month
This is not profit or cash flow. It excludes tax, management, maintenance, insurance, service charges, licensing, safety work, voids, arrears, legal costs, product fees, and capital repayments.
This calculator is for guidance only.
Results are illustrative estimates based on the figures you enter and do not constitute regulated mortgage advice, financial advice, or a binding quote. Mortgage rates and lender criteria change daily. For an accurate quote and advice tailored to your situation, speak to an FCA-authorised mortgage broker. MortgageConnector is not a broker — we are a free service that introduces you to one. Get matched with a broker.
Your home may be repossessed if you do not keep up repayments on your mortgage.
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How the calculation works
- 1. Mortgage required: property price minus cash deposit.
- 2. Stressed monthly interest: mortgage multiplied by the annual stress rate, divided by 12.
- 3. Required rent: stressed monthly interest multiplied by the ICR percentage.
- 4. Rent-supported loan: annual rent divided by the stress rate and ICR.
What this result leaves out
- Product, valuation, legal, and broker fees
- Purchase tax and ownership-structure tax
- Repairs, compliance, management, and insurance
- Voids, arrears, service charges, and ground rent
- Capital repayment on a repayment mortgage
- Property, applicant, portfolio, and lender eligibility
Why lender results can differ
Buy-to-let affordability is not a single market-wide formula. The Prudential Regulation Authority requires regulated firms to use robust interest coverage and affordability stress testing, but lenders set their own detailed ICRs, stress rates, product exemptions, and top-slicing rules within that framework.
A five-year fixed product may be assessed differently from a shorter fix. Personal ownership can be tested differently from a special-purpose vehicle company. Higher-rate taxpayers, first-time landlords, portfolio landlords, HMOs, holiday lets, and multi-unit properties can also follow different criteria. Enter the actual ICR and stress rate supplied for the product rather than treating the defaults as a quote.
Interest coverage is not profit
Passing an ICR test only means the rent clears one lender's mortgage-interest hurdle. It does not show whether the investment works after tax, repairs, agent fees, safety checks, licensing, insurance, service charges, ground rent, void periods, arrears, and capital expenditure. Stress your own cash flow separately and obtain tax advice before deciding how to own the property.
Individual residential landlords generally receive finance-cost relief as a basic-rate tax reduction rather than deducting all mortgage interest from rental income. UK-resident companies are outside that specific restriction, but company ownership introduces corporation tax, extraction, accounting, financing, and future-sale considerations. There is no universal best structure.
Use the result to prepare a broker conversation
Take the following figures to an FCA-authorised broker:
- property price, deposit source, and target loan;
- expected rent supported by an agent's letter or comparable evidence;
- property type, tenancy plan, licence position, and refurbishment needs;
- personal or company ownership, portfolio details, income, and tax advice already received;
- the ICR and stress rate used in this illustration.
Continue with the buy-to-let mortgage guide, limited-company guide, or HMO mortgage guide.
Buy-to-let calculator questions
How do lenders calculate buy-to-let affordability?
Many lenders compare expected rent with mortgage interest calculated at a stressed interest rate. The required interest coverage ratio and stress rate vary by lender, product, tax position, fixed period, borrower, and property. Some lenders also consider personal income through top slicing.
What does 125% ICR mean?
An interest coverage ratio of 125% means the expected monthly rent must equal at least 1.25 times the stressed monthly mortgage interest. It is an underwriting test, not a forecast of profit or cash flow.
Why does the calculator use a stress rate?
The stress rate tests whether rent could cover interest under a less favourable rate assumption. PRA-regulated lenders must have a robust framework, and the supervisory statement specifies a minimum 5.5% stressed rate in some scenarios. Lenders can apply different or higher tests.
Does passing the rental test guarantee approval?
No. Lenders also assess loan-to-value, applicant and company structure, credit, income, landlord experience, property type, valuation, tenancy, licensing, and portfolio exposure. The result is illustrative only.
Does this calculator include tax and running costs?
No. It shows mortgage and rental-stress figures only. Budget separately for transaction tax, income or corporation tax, repairs, insurance, management, service charges, compliance, licensing, voids, arrears, legal work, and mortgage fees. Obtain tax advice before choosing personal or company ownership.
Check the case with a buy-to-let broker
Get introduced to one FCA-authorised broker based on the property, ownership route, and landlord experience.
Find a buy-to-let broker