Buy-to-let mortgage calculator
Monthly payment, total interest, balance at end of term — and the bit most calculators skip: the ICR stress test your lender will run. Find out whether your rent actually qualifies for the loan before you apply.
Property & loan
Most BTL lenders require 25% minimum
Most UK BTL mortgages are interest-only — the loan stays the same at the end.
Rent & stress test
What the lender stresses the rate at — typically 5.5% for 2-year fixes, the pay rate for 5-year fixes
Most lenders: 125% for basic-rate / ltd company
Most lenders: 145% for higher / additional-rate landlords
Loan amount
£150,000
75% LTV · £50,000 deposit
Monthly payment
£687.50
Interest only
Total interest
£206,250
Over 25 years
Balance at end of term
£150,000
Capital still owed — refinance or sell
Lender stress test (ICR)
BTL lenders won't offer the loan unless your annual rent covers the stressed interest-only payment by the required margin. Below shows whether your rent passes for each tax band.
Basic-rate / ltd company — 125% ICR target
Passes stress test
- Your monthly rent
- £1,100
- Minimum needed
- £859
- Your ICR
- 160%
Higher / additional-rate — 145% ICR target
Passes stress test
- Your monthly rent
- £1,100
- Minimum needed
- £997
- Your ICR
- 160%
Section 24 note: if you own the property personally (not in a limited company), mortgage interest is no longer fully deductible — you get a 20% tax credit instead. Higher-rate landlords pay tax on the gross rent and recover only basic-rate relief on the interest. The numbers above are pre-tax — model the after-tax position separately before committing.
Already a landlord? RentFig tracks the real mortgage numbers
Once the mortgage is live, RentFig logs every interest payment, calculates the Section 24 tax credit and feeds straight into your Self Assessment. Free for one property.
Buy-to-let mortgages — FAQ
The most common questions UK landlords ask about BTL mortgages, the stress test and Section 24.
- What is the ICR stress test for buy-to-let mortgages?
- The Interest Cover Ratio (ICR) is the test BTL lenders use to decide whether the rent comfortably covers the mortgage payment. They take the loan, work out the interest-only payment at a 'stress' rate (often 5.5%), then require your annual rent to be a multiple of that — typically 125% for basic-rate or limited-company landlords and 145% for higher / additional-rate landlords.
- What deposit do I need for a UK buy-to-let mortgage?
- Most BTL lenders require a minimum 25% deposit. A small number go to 20% (80% LTV) at higher rates. Specialist HMO and limited-company products usually want 25–30%. Larger deposits unlock better rates — the lowest pricing typically appears at 60% LTV.
- Should I take an interest-only or capital repayment BTL mortgage?
- Most UK landlords take interest-only because the monthly payment is far lower, the interest is what counts for tax purposes (Section 24 aside), and the strategy assumes refinancing or selling at the end of term. Capital repayment makes sense if you want to be mortgage-free in retirement, are prepared to accept lower cashflow, and don't plan to remortgage.
- How is the BTL mortgage stress test different for 5-year fixes?
- Most lenders waive the stressed-rate calculation for 5-year fixes and use the actual pay rate instead. That's because the FCA's affordability rules treat 5-year deals as lower-risk — your rate is locked in for longer, so they don't need to stress for short-term rate rises. This typically means 5-year fixes pass affordability at much lower rents.
- Does Section 24 affect what I can borrow?
- Indirectly — yes. Lenders still apply the 125% / 145% ICR test on the gross stressed payment, but higher-rate landlords need 145% because Section 24 means their after-tax income is significantly lower than their pre-tax rent. Limited companies aren't affected by Section 24 and so usually qualify on the 125% test, which is one of the reasons many landlords incorporate.
- What if my rent doesn't pass the stress test?
- Three options: (1) put down a bigger deposit so the loan is smaller, (2) buy a property with higher yield, or (3) move to a 5-year fixed product where lenders stress at the pay rate. Some specialist lenders also use 'top-slicing', allowing personal income to cover the shortfall.
- Are these the same calculations a lender will use?
- The maths is correct, but every lender sets their own stress rate and ICR percentage. The defaults here (5.5% stress / 125% / 145%) are typical but not universal — some lenders stress higher, some lower, and product transfer pricing is usually more generous. Always confirm with a BTL broker before committing.