Lenders do not just look at your buy-to-let mortgage payment — they check that the rent comfortably covers the interest, even if rates were higher than you actually pay. That test is called the interest coverage ratio (ICR), or rental cover. This calculator lets you model it in seconds.
Enter your expected monthly rent and it shows the maximum loan that rent could support. Add a loan amount and it also shows the rent required to pass, and whether your figures stack up — and by how much. It is built for landlords sizing up a purchase or remortgage, whether buying in a personal name or through a limited company. The result is indicative only: it is a quick sense-check, not a quote or a decision.
How it works
The test compares the annual rent against the mortgage interest calculated at a stressed (notional) rate — a rate set higher than the real pay rate to check the rent would still cover the loan if rates rose. The ratio (the ICR) is the buffer the lender wants on top.
In words:
- Maximum loan = the annual rent (monthly rent multiplied by twelve), divided by the stress rate multiplied by the ICR. A higher rent, a lower stress rate, or a lower ICR all support a larger loan.
- Required rent = the loan, multiplied by the stress rate, multiplied by the ICR, divided by twelve. This is the minimum monthly rent that loan needs to pass.
The two are the same relationship rearranged. The ICR percentages and the stress rate in the tool are typical conventions you can change — they are not current market rates, and every lender applies its own.
A couple of things the calculator deliberately keeps simple. Where a product is fixed for five years or more, lenders often stress more leniently (sometimes at or near the pay rate), which can support a larger loan on the same rent — you can model that by lowering the stress rate. And if the rent is tight, top-slicing may be an option with some lenders: surplus personal or portfolio income is used to help bridge the gap. Not every lender offers it, each sets its own criteria, and leaning on personal income means the property is less self-financing — so treat it as a possible route, not a given.
If you hold four or more mortgaged buy-to-let properties, you are classed as a portfolio landlord under the PRA standards. That brings whole-portfolio underwriting (the lender assesses your entire portfolio, not just the property being financed) and more paperwork, typically a full portfolio schedule. The calculator works on a single property — a portfolio case needs the wider picture.
Frequently asked questions
What ICR percentage should I use? It depends on the lender and on your tax position. Basic-rate taxpayers and limited-company (SPV) borrowers commonly see around 125%, while higher- and additional-rate taxpayers commonly face around 145%, because the tax treatment of rental income leaves them needing a larger buffer. These are typical conventions, not fixed rules — some lenders use intermediate or blended figures. The calculator lets you pick or enter your own.
Why is the stress rate higher than the rate I would actually pay? The stress rate is a headroom test, not your real payment. By checking the rent against a higher notional rate, the lender makes sure the mortgage would still be covered if rates rose. We do not show a live rate, because stress rates move with the market and differ by lender and product — the figure in the tool is an example for you to change.
My rent does not quite cover the loan. Is the deal dead? Not necessarily. You could look at a longer fixed rate (often stressed more leniently), a larger deposit to reduce the loan, or top-slicing with a lender that allows surplus income to support the case. The right route depends on your circumstances, which is where speaking to a specialist helps.
Is the calculator result a mortgage offer? No. It is an indicative sense-check based only on the figures you enter. It is not a personal illustration, a quote, or advice, and it does not guarantee that any lender will lend. A proper assessment looks at your wider income, costs, credit profile, the property, and each lender's exact rules.
Speak to a specialist
We work with more than 135 lenders and can talk through whether your numbers stack up and which routes might fit. Call 020 7126 8574 or request a call back, and we aim to reply within one working day.
Your property may be repossessed if you do not keep up repayments on a mortgage secured on it.
Most buy-to-let mortgages are not regulated by the Financial Conduct Authority. Propertyze is a trading style of City Finance Brokers Ltd, authorised and regulated by the Financial Conduct Authority (FCA No. 766295). We conduct both regulated and unregulated business, so not all products provided through us are regulated by the FCA.
This calculator gives an indicative result only, based on the figures you enter. It is not a personal illustration, a quote, a mortgage offer, or advice.