Buy-to-Let Mortgage Calculator
See whether a buy-to-let stacks up. Work out the rental cover (ICR) lenders stress test, your maximum borrowing, and the rent you need to pass.
How the rental cover test works
Buy-to-let lenders don't just look at the price — they check that the rent covers the mortgage with room to spare. This is the interest cover ratio (ICR). Lenders work out the interest at a higher "stressed" rate than you might actually pay, then ask the rent to cover that interest by a set margin.
The margin is usually 125% for basic-rate taxpayers and 145% for higher-rate taxpayers, because higher-rate landlords keep less of the rent after tax. The stress rate is often around 5.5%, even when fixed deals are cheaper.
If the rent falls short, you have two options: put down a bigger deposit so you borrow less, or find a property where the rent covers the test. This calculator shows the rent you'd need and the most you could borrow on the rent you have.
Frequently asked questions
- What is rental cover (ICR)?
- ICR stands for interest cover ratio. It measures how far the annual rent goes beyond the mortgage interest, worked out at the lender's stress rate. A 145% ICR means the rent must be at least 1.45 times the stressed interest.
- Why is the stress rate higher than my actual mortgage rate?
- Lenders stress test at a higher notional rate (often around 5.5%) to make sure you could still afford the mortgage if rates rose. It's a safety margin, so a cheap fixed deal today still has to pass the stressed figure.
- Should I use 125% or 145%?
- Use 125% if you're a basic-rate taxpayer and 145% if you're a higher-rate taxpayer. Higher-rate landlords keep less of the rent after tax, so lenders ask for more cover. Limited company buy-to-lets often use 125%.
- What if the rent doesn't pass?
- You can lower the loan by putting down a bigger deposit, or look for a property where the rent is higher relative to the price. The calculator shows both the rent you'd need and the maximum loan the current rent supports.
Sizing up a rental?
Get a full read on any listing. Our reports flag the risks, costs, and area data that decide whether a buy-to-let is worth it.
Estimates only, based on the assumptions you enter and current published rates. Not financial advice. Your actual costs depend on your circumstances and your lender. HomeThink is not authorised or regulated by the Financial Conduct Authority and recommends no lender or mortgage.
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