Buy-to-let mortgage calculator
See the monthly payment, whether the rent passes a lender's test, and what the deal leaves you each month.
- Lender rent cover test
- Monthly profit after costs
- Cash you need upfront
£200,000 at £1,100 a month. Get the full deal report.
Area rents and sold prices, yield, cash flow and a summary you can share. AskPortfoliq on WhatsApp and Telegram can run it too.
What is rent cover (ICR)?
Buy-to-let lenders lend on the rent, not your salary. The interest cover ratio (ICR) compares the monthly rent with the monthly interest the lender works out at a stress rate, which is usually higher than the rate you will pay. If the rent covers that stressed interest by enough, the loan passes.
Most lenders ask for 125% cover from basic-rate taxpayers and limited companies, and 145% from higher and additional-rate taxpayers, who get less tax relief on mortgage interest. A few specialist lenders ask more (up to 160%). The test is on interest only, even for a repayment mortgage.
Lender stress rates
Under the Bank of England's rules (PRA SS13/16), lenders test fixes shorter than five years at the higher of the pay rate plus 2 points and 5.5%. Fixes of five years or more can be tested nearer the pay rate, but each lender sets its own floor, so this calculator never uses less than 5.5% or the pay rate.
If a broker has quoted a lender's stress rate, type it into "Lender stress rate" and the test uses it instead.
How much deposit do you need?
Most buy-to-let lenders lend up to 75% of the price, so a 25% deposit is the usual starting point. Some go to 80% or 85%, with higher rates and fewer products. A bigger deposit means a smaller loan, which also makes the rent cover test easier to pass.
Interest-only or repayment?
Most landlords borrow interest-only: the payment is lower, so monthly cash flow is higher, and the loan is repaid when the property is sold or refinanced. A repayment mortgage costs more each month but pays the loan down, so part of each payment builds equity rather than being a cost.
Section 24 in one paragraph
Individual landlords can't deduct mortgage interest from rental income. Instead they get a tax credit of 20% of the interest. A basic-rate taxpayer ends up about where they were, but a higher-rate taxpayer pays 40% tax on rent that went on interest and only gets 20% back, which is why lenders ask them for more rent cover. Limited companies still deduct interest in full before corporation tax.
Worked example: a £200,000 buy-to-let at £1,100 a month
A higher or additional-rate taxpayer puts down 25% and borrows £151,995 interest only at 5.75%, fixed for 5 years or more, with the £1,995 fee added to the loan. The payment is £728 a month.
At a stress rate of 5.75%, the rent covers the interest 151%, against the 145% needed, so it passes. On this rent a lender would lend up to £158,320.
After insurance and 8% for maintenance and voids, that leaves £258 a month before tax. Buying needs £63,000 in cash, including £11,500 Stamp Duty Land Tax in England & NI.
Common questions
- How much can I borrow on a buy-to-let?
- It depends on the rent more than your income. The most a lender will lend is roughly the yearly rent divided by the required cover times the stress rate. At £1,100 a month, 145% cover and a 5.75% stress rate, that is about £158,320. Most lenders also cap the loan at 75% of the price.
- What is a buy-to-let rent cover (ICR) test?
- A check that the rent covers the mortgage interest, worked out at a stress rate, by a set margin. Most lenders ask for 125% for basic-rate taxpayers and limited companies and 145% for higher-rate taxpayers. A few specialist lenders ask more (up to 160%).
- Why do higher-rate taxpayers need 145% rent cover?
- Because of Section 24. They can only claim 20% tax relief on mortgage interest while paying 40% or 45% tax on the rent, so lenders want more rent left over to cover the tax.
- What stress rate do buy-to-let lenders use?
- For fixes under five years, at least the pay rate plus 2 points and never less than 5.5%. Five-year fixes are often tested nearer the pay rate. Each lender has its own figure, so a broker can tell you the exact one.
- What deposit do I need for a buy-to-let mortgage?
- Usually 25%. Some lenders accept 20% or 15%, at higher rates. Limited company mortgages follow similar limits.
- What if my deal fails the rent cover test?
- Put in a bigger deposit, choose a five-year fix (often tested at a lower stress rate), or find a lender that tests at a lower rate or uses your other income (top slicing). The calculator shows the most you could borrow on the rent and how much more deposit that means. Speak to a broker before you offer.
- Is this mortgage advice?
- No. It is a guide to how lenders usually test a buy-to-let. Lenders' criteria differ, so speak to a mortgage broker before you rely on a figure.
Sources
- Bank of England PRA: SS13/16 Underwriting standards for buy-to-let mortgage contracts
- Moneyfacts: buy-to-let mortgage rates
- NRLA: rental stress tests on buy-to-let mortgages
- GOV.UK: Changes to tax relief for residential landlords (Section 24)
- GOV.UK: Stamp Duty Land Tax residential rates
Stress test and starting rate checked on 27 Oct 2026 against the sources above. Guide only, not advice. Each lender sets its own rent cover, stress rate and loan limits, so speak to a mortgage broker before you rely on a figure.
Your next portfolio task could take one message.
Add your first property, connect WhatsApp or Telegram, and put AskPortfoliq to work.
Set up in minutes · Cancel anytime · AskPortfoliq included on every plan