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.
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