Buy To Let Rental Income Calculator

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

When applying for a buy-to-let mortgage, lenders don’t just look at your personal income. Instead, they assess whether the rental income from the property is sufficient to cover the mortgage interest payments.

This is known as the rental cover ratio or interest cover ratio (ICR).

Most lenders require the expected rent to exceed the mortgage interest payment by a set percentage. This helps ensure the property remains affordable, even if interest rates rise or the property is temporarily vacant.

What is the rental stress test?

A buy-to-let stress test is used by lenders to calculate the minimum rental income required for a mortgage to be approved.

Rather than using the actual mortgage rate, lenders often apply a stress rate (commonly around 5.5% or higher) and then apply an ICR, such as:

• 125% – typically used for basic rate taxpayers or some limited company applications
• 145% – commonly used for higher or additional rate taxpayers
• 160%+ – often applied to HMOs or more complex cases

This means the rent must be significantly higher than the mortgage interest alone.

How is rental income calculated for buy-to-let?

The calculation used by most lenders follows this structure:

Monthly interest payment × ICR = Minimum required rent

For example:

• Mortgage: £200,000
• Stress rate: 5.5%
• Monthly interest: £916
• ICR: 145%

Minimum rent required: £1,328 per month

This is why some properties may appear affordable based on price alone, but fail the lender’s rental stress test.

Why loan-to-value (LTV) matters

Your loan-to-value (LTV) also plays a key role.

A typical buy-to-let mortgage is based on:

• 75% LTV (25% deposit)

A higher LTV means:

• larger mortgage
• higher monthly interest
• higher rental income is required

Some lenders may allow higher or lower LTVs, but this will depend on:

• the property type
• your experience as a landlord
• your tax position
• lender-specific criteria

Important things to keep in mind

This calculator provides a useful estimate, but real-world lending decisions can vary.

Lenders may also consider:

• whether you are a portfolio landlord
• if the property is a standard BTL or HMO
• your tax band or ownership structure
• fixed vs variable rate products
• local rental demand and property type

Different lenders apply different rules, so passing one lender’s stress test does not guarantee approval elsewhere.

Planning a buy-to-let investment

Understanding rental affordability is just one part of the picture.

A well-structured buy-to-let strategy should also consider:

• long-term interest rate changes
• void periods and maintenance costs
• tax efficiency (especially for limited companies)
• future refinancing options

This is where tailored advice can make a significant difference — particularly if you are building or expanding a property portfolio.