Buy-to-let mortgage calculator

A buy-to-let lender asks whether the rent covers the interest, not whether your salary does. Enter a price and a rent to see the payment, and the loan the rent supports.

Monthly mortgage payment

£461

Interest-only on a £112,500 loan, 75% of the price

Rent less the payment: £289
Repayment instead: £652
Interest over the term: £138,375

Before letting fees, maintenance, insurance, empty months and tax, which usually take 25% to 35% of the rent between them; see running costs and voids.

The lender's rental cover test

The rent has to cover the interest by a margin, worked out at 4.92% (the pay rate, which lenders may use on a fix of five years or more). That is £461 a month of interest to cover.

At 125% cover

Passes

Basic-rate taxpayers, and most limited company lending

Rent needed: £577 a month
Cover achieved: 163%
Largest loan the rent supports: £146,341
Smallest deposit it allows: £3,659

At 145% cover

Passes

Higher and additional-rate taxpayers

Rent needed: £669 a month
Cover achieved: 163%
Largest loan the rent supports: £126,156
Smallest deposit it allows: £23,844

Where the rent allows a smaller deposit than 25%, most lenders still ask for 25%. Lenders set their own tests, and some also look at your income or other properties.

How the calculator works

The payment is the interest on the loan each month for an interest-only mortgage, or the fixed monthly amount that clears the loan over the term for a repayment one.

The rental cover test divides the rent by the interest, worked out at a stress rate. On a fix shorter than five years the stress rate is the pay rate plus two points, or 5.5% if that is higher; on a fix of five years or more it can be the pay rate. That follows the Prudential Regulation Authority's underwriting standard, which lenders then apply in their own way. Turning the test around gives the largest loan the rent supports, and the price less that loan is the smallest deposit the rent allows.

The same test runs in every Clarity location report, so a loan that passes here passes there. For the reasoning behind it, and a worked example, read buy-to-let mortgages explained. To cost the rest of the purchase, use the stamp duty calculator.

Frequently asked questions

How much rent do I need for a buy-to-let mortgage?: Enough to cover the interest by 125% or 145%, worked out at a stress rate rather than the rate you pay. On a £112,500 loan stressed at 5.5%, the interest is about £516 a month, so a basic-rate taxpayer needs about £645 of rent and a higher-rate taxpayer about £748.
Which cover ratio applies to me?: Most lenders ask for 125% from basic-rate taxpayers and 145% from higher and additional-rate taxpayers, because the higher-rate landlord keeps less of the rent after tax. Lending to a limited company is usually tested at 125% whatever the director's tax band.
Why does a five-year fix let me borrow more?: The Prudential Regulation Authority expects lenders to test a shorter fix at the pay rate plus two points, or 5.5% if that is higher, but allows a fix of five years or more to be tested at the pay rate itself. A lower test rate means less interest to cover, so the same rent supports a bigger loan.
Should I choose interest-only or repayment?: Most landlords choose interest-only, because the payment is lower and the rental cover test is run on interest either way. The loan is still owed in full at the end of the term, so it suits a plan to sell, refinance or pay it off from savings. Repayment costs more each month and leaves the property owned outright.

Sources and further reading

Bank of England PRA: SS13/16 Underwriting standards for buy-to-let mortgage contracts

An illustration of the arithmetic, not a mortgage offer or advice. The rates are examples, and each lender sets its own stress rate, cover ratios, fees and maximum loan. Speak to a broker authorised by the Financial Conduct Authority before you borrow.

Written by the Clarity Property Investments research team. Last reviewed 29 September 2026. This article is general information, not financial or tax advice.

How the calculator works

The payment is the interest on the loan each month for an interest-only mortgage, or the fixed monthly amount that clears the loan over the term for a repayment one.

Frequently asked questions

How much rent do I need for a buy-to-let mortgage?

Enough to cover the interest by 125% or 145%, worked out at a stress rate rather than the rate you pay. On a £112,500 loan stressed at 5.5%, the interest is about £516 a month, so a basic-rate taxpayer needs about £645 of rent and a higher-rate taxpayer about £748.

Which cover ratio applies to me?

Most lenders ask for 125% from basic-rate taxpayers and 145% from higher and additional-rate taxpayers, because the higher-rate landlord keeps less of the rent after tax. Lending to a limited company is usually tested at 125% whatever the director's tax band.

Why does a five-year fix let me borrow more?

The Prudential Regulation Authority expects lenders to test a shorter fix at the pay rate plus two points, or 5.5% if that is higher, but allows a fix of five years or more to be tested at the pay rate itself. A lower test rate means less interest to cover, so the same rent supports a bigger loan.

Should I choose interest-only or repayment?

Most landlords choose interest-only, because the payment is lower and the rental cover test is run on interest either way. The loan is still owed in full at the end of the term, so it suits a plan to sell, refinance or pay it off from savings. Repayment costs more each month and leaves the property owned outright.