Finance & Business
Buy to Let Mortgage Calculator
Calculate your buy to let mortgage payments, rental yield, and cash flow. Check if your property meets lender stress test requirements.
Enter your property details to see the buy to let analysis
Related to Buy to Let Mortgage Calculator
This calculator estimates the monthly mortgage payment on a buy-to-let property under both interest-only and repayment structures, calculates gross and net rental yields, and applies the lender stress test to indicate whether your projected rental income would be sufficient to satisfy typical UK buy-to-let mortgage criteria.
Interest-Only vs Repayment
On an interest-only mortgage, the monthly payment is simply: M = (loan amount × annual interest rate) ÷ 12. The capital balance remains unchanged throughout the term and must be repaid in full at the end — typically from the sale of the property. On a repayment mortgage, the standard amortisation formula applies: M = P × [r(1 + r)^n] ÷ [(1 + r)^n − 1], where P is the loan, r is the monthly rate, and n is the total number of monthly payments. Most UK buy-to-let investors use interest-only mortgages to maximise monthly cash flow, though repayment offers the certainty of full equity ownership at the end of the term.
Rental Yield Calculations
Gross rental yield is calculated as: (annual rent ÷ property value) × 100. It provides a quick comparison metric between properties before costs are considered. Net rental yield refines this by deducting annual costs (mortgage interest, letting agent fees, insurance, maintenance, void periods, and management) from the annual rent before dividing by property value: net yield = (annual rent − annual costs) ÷ property value × 100. Net yield is the more meaningful figure for assessing actual return, as gross yield can flatter properties with high running costs.
Lender Stress Test (Interest Coverage Ratio)
UK buy-to-let lenders do not assess affordability on income in the same way as residential mortgages. Instead, they apply an Interest Coverage Ratio (ICR) test: monthly rent must exceed a notional monthly interest payment by a specified margin. For basic-rate taxpayers, most lenders require rent to cover at least 125% of the mortgage interest, calculated at a stressed rate of around 6%. For higher or additional rate taxpayers (or in a limited company with the wrong tax profile), the required ICR is typically 145% at the same stressed rate. The calculator applies these thresholds to show whether your rental income passes or falls short of the lender test.
Loan-to-value (LTV) is the mortgage amount expressed as a percentage of the property value. Most buy-to-let lenders lend up to 75% LTV (requiring a 25% deposit), and the most competitive rates are available at 60% LTV or below. A higher LTV not only restricts available products but also increases the mortgage payment and reduces your monthly cash flow and net yield.
The results give you the monthly mortgage payment, gross and net yields, monthly cash flow after mortgage costs, and whether the property passes the lender stress test. Use these figures together to build a complete picture of the investment rather than relying on a single metric.
What Makes a Good Rental Yield in the UK?
As a general benchmark, a gross yield of 5–6% or above is considered reasonable for UK buy-to-let in 2025, though yields vary significantly by region. Northern cities such as Manchester, Liverpool, and Leeds often achieve gross yields of 6–8%, while prime London properties can fall below 3%. Net yield, after all costs, is typically 1.5–2 percentage points lower than gross yield. A property yielding less than 4% gross may struggle to pass the lender stress test or generate meaningful monthly cash flow, particularly at higher LTVs.
Stress Test Pass or Fail
A stress test pass means that at the lender's notional stressed rate (typically 6%), the monthly rent covers the required ICR multiple (125% for basic-rate taxpayers, 145% for higher-rate). A fail does not necessarily mean the investment is unviable — it may mean you need a larger deposit to reduce the LTV, or that you should approach specialist lenders with different ICR criteria. Some lenders also offer top-slicing, which allows other personal income to supplement rental income to meet affordability.
Monthly cash flow — rent minus mortgage payment and running costs — is the most immediate measure of whether a property pays for itself each month. Positive cash flow of at least £100–£200 per month is generally sought to provide a buffer against void periods and unexpected maintenance. Return on deposit (annual profit ÷ deposit paid) can be significantly higher than the net yield on the property value, because leverage amplifies the return on the capital actually invested.
1. What rental yield should I aim for on a buy to let property?
A gross rental yield of 5–6% is a commonly used minimum target for UK buy-to-let in 2025, though the right figure depends on your financing costs, tax position, and investment objectives. At higher LTVs (70–75%), a gross yield of at least 6–7% is usually needed to achieve positive cash flow after mortgage payments and costs. At lower LTVs or when purchasing with cash, a yield of 4–5% may still generate a satisfactory net return. Always calculate net yield after accounting for all costs, including void periods (typically budgeted at 4–6 weeks per year), letting agent fees (8–15% of rent), insurance, and maintenance reserves.
2. What is the lender stress test for buy to let mortgages?
Buy-to-let lenders assess affordability using an Interest Coverage Ratio (ICR) rather than personal income. The test asks whether the monthly rent covers a notional interest payment — calculated at a stressed rate (commonly 5.5–6%), which is higher than the actual product rate — by the required multiple. Basic-rate taxpayers typically need rent to be at least 125% of the stressed interest payment; higher-rate taxpayers or limited companies taxed as higher rate typically need 145%. For example, a £200,000 mortgage at a 6% stressed rate produces a notional monthly interest of £1,000; at 125% ICR, the minimum required rent is £1,250 per month.
3. Should I choose interest-only or repayment for buy to let?
Most UK buy-to-let investors choose interest-only mortgages because the lower monthly payment maximises cash flow and makes it easier to pass the lender stress test. The trade-off is that the capital balance is not reduced over time, so you rely on property price growth or savings accumulated elsewhere to repay the loan at the end of the term. Repayment mortgages are less common in buy-to-let but suit investors who prefer to own the property outright at the end of the term or who want to reduce exposure to future refinancing risk. A repayment structure also builds equity faster, which improves LTV and can unlock better rates on future remortgages.
4. What costs should I include in my buy to let calculations?
A comprehensive buy-to-let cost calculation should include: mortgage interest payments; letting agent fees (fully managed services typically cost 12–15% of monthly rent including VAT); landlord insurance (buildings and contents); annual gas safety certificate and any required electrical installation condition reports; maintenance and repairs (a common rule of thumb is to budget 1% of property value per year); void periods between tenancies (budget for 4–6 weeks per year); accountancy fees if operating through a limited company; and Stamp Duty Land Tax on the purchase (the additional property surcharge of 5% applies to buy-to-let purchases). Section 24 of the Finance Act 2015 also limits mortgage interest tax relief to the basic rate for individual (non-company) landlords, which significantly reduces net returns for higher-rate taxpayers.
5. What is the scientific source for this calculator?
The interest-only and repayment mortgage payment formulas follow standard financial mathematics as applied by UK lenders and set out in the FCA Handbook MCOB 10. Rental yield formulas are standard investment property metrics consistent with guidance published by the Royal Institution of Chartered Surveyors (RICS) and widely used by UK property investment analysts. The Interest Coverage Ratio stress test parameters — 125% ICR for basic-rate taxpayers, 145% for higher-rate taxpayers, and a notional stressed rate of 6% — are based on the Prudential Regulation Authority's supervisory statement SS13/16 ("Underwriting standards for buy-to-let mortgage contracts"), which sets out the minimum standards UK lenders must apply when assessing buy-to-let affordability. Tax treatment references are based on Finance Act 2015 (Section 24) as amended by Finance Act 2017.