An Income Boost is a little-known guarantor mortgage scheme that lets someone close to you – like a parent, sibling, or even a friend – help your application without giving (or lending) you money. Their income gets added to yours, so you can borrow more without upping your deposit. That extra boost could be the difference between “almost there” and “keys in hand.”
What is an Income Boost Guarantor Mortgage (Joint Borrower Sole Proprietor)?
It’s a type of mortgage that lets you add up to four people (usually family) to your application as joint borrowers. Their income gets included when the lender crunches the numbers, meaning a bigger loan offer for you.
But only your name goes on the property deeds – that’s the “sole proprietor” bit. So while they don’t own your home, they do share the legal responsibility for repayments. If you stop paying, they’ll need to cover it.
Why would you an Income Boost Guarantor Mortgage?
It’s smart if you’ve got great earning potential but not-so-great income right now. Example: on a £25,000 salary, you might only be able to borrow £100k–£112.5k. But with Mum’s £38,000 added in, you might be able to stretch to £252k–£283.5k. That’s up to £152k more – a game-changer for your home search.
When can a joint borrower be removed from the mortgage?
Your joint borrower can be taken off the mortgage once your financial position improves and you can afford the mortgage by yourself; for instance, if your income increases to a level where you can borrow the mortgage you need without your guarantor’s income. Alternatively, they can come off if you choose to remortgage (subject to affordability) or sell the property.
What happens if a joint borrower passes away?
If the person supporting your mortgage passes away and you’re unable to afford the repayments on your own, it could mean having to sell the property, unless you’ve planned ahead. It’s always advisable to speak to a financial advisor before setting it up.
- Is there an age limit for joint borrowers?
- Yes. Lenders want the mortgage cleared by age 80. So for a 35-year term, your helper needs to be 45 or younger. Something to keep in mind if Mum or Dad are stepping in.
Nope. Only the sole proprietor (you) can live in the property. Even though they’re on the mortgage, joint borrowers can’t move in.

This blog post has been written in partnership with Tembo. For more information or to book a call with Tembo, click here.
Subject to affordability and eligibility criteria. Your home may be repossessed if you do not keep up with mortgage payments.
Being added to a borrower’s Joint Borrower Sole Proprietor mortgage (Income Boost) as a joint borrower could impact the guarantor’s ability to get credit in future.