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What is a Joint Borrower Sole Proprietor Mortgage?

Anya Gair
Last Updated 13 June 2024

A joint borrower sole proprietor mortgage is a way to increase the amount you can borrow by adding a friend or family member's income to your mortgage application.

In this guide

What is a Joint Borrower Sole Proprietor mortgage?

With property prices soaring, and half the number of first-time buyers there were versus 20-years ago, a joint borrower sole proprietor mortgage is a great solution for would-be buyers.

Never heard of a JBSP mortgage? No problem, they are still pretty under the radar – but you’re about to find out all you need to know.

See if you're eligible for a Joint Borrower Sole Proprietor mortgage today

Create a free Tembo plan to see if you qualify for a JBSP mortgage, as well as over 15 other specialist buying schemes. It takes 10 minutes to complete, and there's no credit check involved. At the end, you'll get your own personalised recommendation.

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What is a joint borrower sole proprietor mortgage?

A joint borrower sole proprietor mortgage is a mortgage where the home buyer can add either a family member or friend's income onto their mortgage application. This specialist mortgage is a way for a family member or friend to help a buyer increase their affordability, without handing over any cash. It's a particularly good option for buyers who are still early on in their careers, so might be on lower salaries for the next few years, but expect their earnings to rise. Only the buyer will own the property (the "sole proprietor"), but your loved one will be on the mortgage as a "joint borrower", which means they will be liable to pay the mortgage if you cannot.

At Tembo, we call this an Income Boost. An Income Boost increases the amount that the buyer could afford, because the application is based on a higher combined income. It can also reduce the amount of house deposit required.

A joint borrower sole proprietor mortgage is useful for home buyers on lower salaries, as they can get on the ladder sooner or and afford more expensive properties than they would be able to afford by themselves.

You might also like: Buying a house on your own: How to do it and is it right for you?

Interested in seeing how much you could afford with an Income Boost?

Get a mortgage sooner, and for less with an Income Boost. To get started, simply create a free Tembo plan. It only takes 10 minutes to complete, there's no credit check involved and you'll get a personalised recommendation at the end.

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Joint Borrower Sole Proprietor Mortgage Example

Meet Hannah. In her mid-twenties trying to buy a home, Hannah earns £25,000 a year. Multiplying her earnings by 4 (a common sum used by lenders to work out how much they are willing to lend for a mortgage) gives Hannah £100,000 to buy a home.

With the average UK house price now around £230,00, without a very large deposit Hannah won’t be able to buy a property.

How can a JBSP mortgage help Hannah?

With a JBSP mortgage a parent or grandparent, for example, can add their income into the mix to increase the amount Hannah can borrow.

So if we take Hannah’s £25,000 income, and add to it her mum’s income of £38,000, that gives Hannah a total income (after the ‘boost’) of £63,000.

£63,000 x 4 (in the typical way lenders do for mortgages) = £252,000

That’s £152,000 more than on her own

With a deposit of £20,000 to £30,000, Hannah is in a much better position to grab her dream home with a JBSP mortgage.

Pros and cons of a Joint Borrower Sole Proprietor mortgage


A JBSP mortgage can be a good alternative to a typical joint mortgage. In both cases all parties are equally responsible for repaying the mortgage. But with a JBSP mortgage, because only the homeowner has their name on the property deeds, only they benefit from its value. This means that the other parties don’t usually have to pay capital gains tax or the 3% stamp duty surcharge

Having a higher income, boosted by a loved one with a joint borrower sole proprietor mortgage, may mean the homebuyer can achieve their homebuying dream with a smaller deposit. This can mean they are able to buy a property sooner, potentially savings thousands of pounds in rent.


All borrowers on the mortgage application will need to pass a credit check. Even if a parent is a higher earner and wants to help boost the income of their son or daughter to help them on the property ladder, if they are overcommitted with their own borrowings and outgoings – maybe their own mortgage is still big, or they have a lot of credit card debt – that will be a problem.

All of those named on the mortgage application will be liable for repaying the mortgage, but only the homeowner has any rights to the value in the property. So parents (or grandparents) who put their income at risk in this way will have no corresponding rights.

When would a Booster come off the mortgage?

  • If the homebuyer’s salary increased such that they were able to guarantee the mortgage and afford the monthly repayments on their own
  • If the homebuyer agreed to sell
  • If the relationship with the income booster broke down and they could get a deed of release from the lender, unlikely to if the homeowner cannot afford the mortgage

What happens if the Booster dies?

 If the homebuyer can’t afford the mortgage repayments on their own they may have to sell the property.

What is the maximum age limit for an Income Boost?

The length of the mortgage term the homeowner is allowed will depend on the age of the oldest person named on the application. Most lenders require a mortgage to be paid off by age 80. This may limit your term if your boost is coming from a parent or grandparent, and so make monthly repayments higher.


Top tip

Joint borrower sole proprietor mortgages can work out a cheaper and more convenient option for parents or grandparents trying to help sons, daughters and grandchildren onto the housing ladder.

If your parents would prefer to contribute to your deposit, Tembo can also advise on a Deposit Boost mortgage. This unlocks money from your family member's existing property and uses that cash to either top up your deposit or create one from scratch.



Mortgage Advisor at Tembo

Why Tembo?

We help buyers, movers and homeowners discover how they could boost their affordability in 3 simple steps. It’s why we’re the UK’s Best Mortgage Broker.


Can the person live with me in the property who is joint borrower?

No. Only the homeowner can live at the property.

Which banks offer joint borrower sole proprietor mortgages?

Many high-street mortgage lenders and banks offer joint borrower sole proprietor mortgages, including:

  • Virgin Money
  • Nationwide
  • Bluestone
  • Clydesdale Bank
  • Post Office Money

Those below also offer joint borrower sole proprietor mortgages, but under specific conditions:

  • Norton Home Loans
  • Dudley Building Society
  • Skipton Building Society
  • Melton Building Society

This list of lenders is non-exhaustive and could change at any time. Each lender will have its own criteria and restrictions on who it will lend to using a JBSP mortgage, and within which rules. For the most up-to-date information, and to see all of your options, it’s a good idea to speak to a specialist mortgage broker.

Moving out of a rental property and into their own home sooner using a Joint Borrower Sole Proprietor mortgage can save the homebuyer thousands of pounds.

All financial products come with risks however. It’s important to weigh up the pros and cons for your individual circumstances using an independent mortgage broker, like Tembo.

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