What is an Income Booster Mortgage?

Income Booster Mortgages Explained: What Borrowers Need to Know

For many borrowers, especially first-time buyers, affordability can be one of the biggest barriers to buying a home. In response, some mortgage lenders offer what are commonly referred to as “Income Booster” mortgages.

This guide explains what an income booster mortgage is, how it works, and what borrowers should understand before considering this type of lending.

“Income Booster” refers to a Joint Borrower, Sole Proprietor (JBSP)-style mortgage where a supporter’s income is used alongside the applicant’s income to increase borrowing capacity, without the supporter becoming an owner of the property.

What Is an Income Booster Mortgage?

An Income Booster mortgage — sometimes also referred to as a Joint Borrower, Sole Proprietor (JBSP) mortgage — is a type of mortgage application structure where family members are added to the mortgage application so that their incomes are included in the affordability assessment, even though they do not become legal owners of the property.

Key Features:

✅ Additional party’s income is included in the calculation to potentially increase how much can be borrowed.
✅ The supporter is jointly responsible for repayments, even though they are not on the property title.
✅ The applicant can remain the sole legal owner of the property.
✅ Supporting parties usually must receive independent legal advice and meet the lender’s affordability and credit criteria.

This structure can help applicants — especially first-time buyers — meet lenders’ affordability requirements when their own income alone would not support the level of borrowing needed.

How It Works

Instead of a standard mortgage application where only the borrower’s income is considered:

  • A parent, close family member can be added to the application as a “booster” (or supporting applicant). Skipton Building Society

  • The lender adds all incomes together when calculating how much the household may be able to borrow.

  • The primary applicant remains the legal owner, while the booster is legally responsible for the mortgage debt if repayments are not met.

This is different from:

  • A gifted deposit — where money is given but the supporter isn’t on the mortgage, and

  • A joint owner mortgage — where everyone on the mortgage is also an owner of the property.

Example (Illustrative Only)

Suppose a first-time buyer earns £36,000 a year. On their own, a lender might allow borrowing up to a certain amount based on that income and the lender’s multiples.

If a parent with a £40,000 income is added as an income booster, their income may be included in the affordability assessment — potentially increasing the amount the applicant may be able to borrow.

Importantly, this doesn’t guarantee approval — all parties must satisfy affordability, credit checks, and lender criteria.

Risks and Considerations

Any income booster arrangement involves important risks and responsibilities:

  • The supporting party is jointly responsible for mortgage repayments, which can affect their future borrowing capacity and credit profile.

  • It may limit options if, at a later date, the primary borrower wants to remove the supporter or remortgage.

  • Independent legal advice is typically required to ensure everyone understands the implications.

Because this type of mortgage involves multiple incomes and legal responsibilities, it’s essential to get professional mortgage and legal advice before proceeding.

Sources & Credits

Information referenced in this article has been sourced from publicly available lender materials, including:

Final Thoughts

A mortgage is one of the biggest financial commitments you’ll ever make, so it’s important to understand how it works before you proceed.

Always speak to a qualified mortgage adviser who can assess your personal situation and help you find the most suitable option.

This article is intended for general information only and does not constitute financial advice. Always seek personalised advice from a qualified mortgage adviser before making any financial decisions.

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