Buy-to-Let Mortgage Calculator

How much can you borrow on a buy-to-let?

Lenders run two checks and lend the lower figure. The first is the rental test in the Bank of England's supervisory statement SS13/16: the rent must cover the mortgage interest, worked out at a stressed rate, by a minimum ratio called the interest cover ratio (ICR). The second is the lender's own loan to value (LTV) limit, often 75%.

Maximum loan = monthly rent ÷ (ICR x stress rate ÷ 12)

Which ICR? Many lenders ask for 125% from limited companies and basic-rate taxpayers and 145% from higher and additional-rate taxpayers, because individuals only get a basic-rate tax credit on mortgage interest. Some ask for more, such as 155% or 160%. Lenders usually add the new rent to your income before they decide your band.

Which stress rate? On a fix of under five years, SS13/16 sets a minimum, not one formula: the lender must allow for rates rising by at least 2 points and assume at least 5.5%. This calculator assumes the higher of the pay rate plus 2 points and 5.5%. Some lenders stress their reversion rate instead, or add more, so their limit can be lower than ours. On a fix of five years or more they can test at or near the pay rate, so a five-year fix often supports a bigger loan. Some lenders set their own minimum on longer fixes; the calculator does not model those.

Worked example. A £200,000 house let at £1,100 a month, a 145% ICR and a 7% stress rate: £1,100 ÷ (1.45 x 0.07 ÷ 12) = £130,049. The 75% LTV cap is £150,000, so the rent decides: you could borrow £130,049 and would need a £69,951 deposit. To borrow the full £150,000, the rent would need to be £1,269 a month. At 125% the rent supports £150,857, so the LTV cap binds instead.

More in how much can I borrow on a buy-to-let and how ICR works. To test one loan amount against the rent, use the mortgage stress test.

Interest-only or repayment?

Interest-only keeps the monthly payment low: you pay only the interest and still owe the whole loan at the end, to clear by selling or remortgaging. Repayment costs more each month but clears the loan over the term. On £150,000 at 5.5% over 25 years, interest-only is £687.50 a month and repayment is £921.13, but repayment pays £79,911 less interest over the term.

Most lenders run the rental test on the interest, so choosing repayment does not usually cut how much you can borrow. The rent still has to cover the bigger payment, along with your other costs. Buy-to-let mortgage rates in October 2026 compares the two at the latest average rates.

Remortgaging a buy-to-let

When a fix ends, the remortgage mode compares your payment now with the payment on the new deal. It assumes your current rate would carry on unchanged; if you would move to the lender's standard variable rate, enter that as the current rate.

Adding the product fee to the loan saves cash today, but you pay interest on it for the whole term. The new loan, fee included, is then checked twice: the ICR at the new pay rate, and the ICR at the lender's stress rate against the 125% or 145% it needs.

Raising money. The most you could borrow is the lower of the rental cap and the LTV cap at today's value; anything above your new loan is what you could raise, before fees on the extra. With the mode's starting figures, £150,000 owed on a £250,000 property, a two-year fix at 5.5% with a £1,999 fee added and £1,500 rent, the rent supports £165,517 at a 145% ICR and a 7.5% stress rate, so you could raise about £13,518.

A like-for-like remortgage with no extra borrowing, or a product transfer with your current lender, may be tested more lightly: SS13/16 makes exceptions for some remortgages with no extra borrowing. Ask your broker how your lender will test yours, and read remortgaging a buy-to-let in 2026 for the options when a fix ends.