Joint Borrower Sole Proprietor mortgages, or JBSP for short, are one of the most genuinely useful tools for first-time buyers whose income alone does not quite stretch to the property they want. They are also one of the most misunderstood. Two myths in particular come up almost every time we have this conversation, and both can put families off a route that would actually have worked for them.
This guide walks through how JBSP mortgages work, who they suit, the stamp duty position, how they differ from a guarantor mortgage, and the single most important question to ask before you apply.
What is a Joint Borrower Sole Proprietor mortgage?
A JBSP mortgage is a mortgage where more than one person is named on the application and is jointly responsible for the repayments, but only one person owns the property and goes on the title deeds.
The supporting borrower, often a parent or family member, joins the application so their income can be used to boost affordability. They take on the legal liability for the mortgage payments, but they have no ownership of the property. That sits entirely with the main borrower, who will live in the home.
How is a JBSP different from a standard joint mortgage?
The key difference is who ends up on the property deeds.
On a standard joint mortgage, all parties named on the mortgage are also named on the deeds, which means everyone has a legal share in the property.
On a JBSP, the supporting borrower is on the mortgage application but not on the deeds. They have no right to the property, no share in any increase in value, and no claim if the property is later sold. Their role is purely to support the affordability of the application.
Why do people choose a JBSP mortgage?
The main reason is affordability. The buyer’s own income does not quite reach what they need to borrow for the property they want, and they need a boost.
A JBSP gives parents and other family members a way to help out without having to hand over a large cash gift. Rather than topping up the deposit, they put their income behind the application. For families who are happy to help but do not have a lot of spare cash sitting around, that can be the difference between the property being possible now and the buyer waiting another two or three years.
Who can go on a JBSP mortgage?
In practice, most JBSP applications involve parents helping a child. But it does not have to be parents. Siblings supporting a sibling is common, and we have seen plenty of cases involving in-laws as well, where one side of the couple has the stronger income and goes on the application to help the other through.
Lender criteria varies on exactly who is eligible. Most lenders restrict JBSP to immediate family; some will consider wider family, and a smaller number will look at unrelated parties. As a rule of thumb, if there is a clear family relationship and a clear reason for the support, there will usually be a lender that fits.
Myth 1: A JBSP mortgage is the same as a guarantor mortgage
This is the most common confusion, and it matters because the liability profile is very different.
A guarantor mortgage, which used to be the standard family-assisted route, sat outside the mortgage itself. The guarantor was a backup. They were only liable if the main borrower defaulted, and they typically secured that backup with savings, an asset, or in some cases a charge against their own home. They did not go on the mortgage application itself.
A JBSP is structured very differently. The supporting borrower is on the mortgage application from day one, with joint and several liability for the payments. That means if the main borrower stops paying, the supporting borrower is not just on the hook in some abstract sense. They are legally responsible for ensuring the full monthly payment is made, exactly as if it were their own mortgage. A missed payment also affects their credit file.
JBSP has largely replaced traditional guarantor mortgages in the residential market because lenders find it cleaner: everyone is on the mortgage, everyone is liable, the structure is simple.
Because of the liability the supporting borrower takes on without gaining any ownership, lenders require them to take independent legal advice before the mortgage completes. That is not a barrier, it is a feature, and it makes sure everyone going into the arrangement properly understands what they are signing up to.
Myth 2: Parents on a JBSP have to pay the second home stamp duty surcharge
A lot of parents are nervous about going on a JBSP because they already own a home of their own, and they assume they will be hit with the additional property stamp duty surcharge (currently 5% on top of standard rates in England and Northern Ireland, having increased from 3% in October 2024).
They do not.
The surcharge applies to people who go on the deeds of an additional property, taking ownership of it. On a JBSP, the supporting borrower is not on the deeds. They have no ownership of the property, no claim to it, and no share in its value. They are only on the mortgage application to support affordability.
So even if the supporting borrower already owns their own home, they pay no stamp duty surcharge on the JBSP property. The only stamp duty due is the stamp duty owed by the person actually buying the home, calculated on their own situation (first-time buyer relief, standard rates, and so on).
This is one of the main reasons JBSP works so well as a family-assistance route: the parent or family member can support the application without triggering a tax bill that would often outweigh the benefit.
(Stamp duty rules differ in Scotland, which uses Land and Buildings Transaction Tax with an Additional Dwelling Supplement, and in Wales, which uses Land Transaction Tax with separate higher rates. The principle that the JBSP supporting borrower is not on the deeds, and therefore is not the one liable for any additional property surcharge, applies across all of the UK.)
Does a JBSP work the same way on a new build?
Yes in principle, with one practical consideration.
JBSP mortgages can be used on new builds, existing homes, flats and houses. The structure is the same. What changes is the LTV cap.
Lenders typically have separate criteria for JBSP and for new build, and they apply the more conservative of the two. So a lender that goes up to 90% LTV on JBSP for an existing property may cap the same JBSP at 85% on a new build flat, because their new build criteria caps at 85%.
That can be a meaningful difference on a 5% deposit budget. So before you settle on a property type, it is worth running both scenarios past a broker: what your borrowing looks like on an existing property versus a new build, and where the LTV caps land. That way you know what you are working with before you put an offer on anything.
What should you think about before applying for a JBSP mortgage?
The mortgage criteria for JBSP is not dramatically different from a standard application. The LTV bands move slightly, with some lenders going up to 95%, so a 5% deposit can be possible. Affordability uses the combined incomes of everyone on the application, with credit commitments and existing mortgages taken into account in the usual way.
A few specific things are worth thinking about:
- Deposit. As above, some lenders go to 95% LTV, but the rate improves as the deposit increases. The standard considerations on deposit size apply.
- Age limits. Lenders often cap the maximum mortgage term based on the supporting borrower’s age. If a parent in their early 60s is going on the application, the lender may shorten the term to keep things within the supporting borrower’s expected working life, which can affect monthly affordability.
- Independent legal advice for the supporting borrower. This is a lender requirement and a sensible safeguard. Plan for it in the timeline.
- Existing credit commitments on the supporting borrower. Their existing mortgage, car finance, credit cards and so on all factor into what extra borrowing their income can actually support.
The single biggest factor: who you add to the application
The mistake we see most often is people assuming that if a family member has a high income, they will automatically be useful on the application.
That is not quite how it works.
The lender brings the supporting borrower onto the affordability assessment in the same way they bring anyone onto a mortgage. Their income is taken into account, and so are their existing commitments. So if your mum earns a strong salary but has a sizable mortgage on her own home with your dad, plus a car loan and some credit cards, the lender deducts the cost of all of that from her income before working out how much of it is genuinely available to support your mortgage. In some cases, that leaves her contribution at close to zero.
That does not mean a JBSP cannot work, but it does mean the right starting question is not “how much deposit do I need?” or “how much can I borrow?”. The right starting question is “who in my family would be in a strong position to go on a JBSP application with me, and would they be happy to?”
Once you have a sense of that, the rest of the application is fairly mechanical. But getting the supporting borrower decision right is what determines whether a JBSP is actually going to lift your affordability or just complicate the application. That is the conversation worth having with a broker first, before anything else.
Why first-time buyers choose Heron Financial for JBSP mortgages
Heron Financial is a B Corp certified, whole of market mortgage broker, and we arrange JBSP mortgages regularly for first-time buyers being supported by parents, siblings and wider family. We work through the parts that most often trip families up, including how new build LTV caps interact with JBSP criteria, age limits on the supporting borrower, and the affordability impact of existing mortgages and credit commitments on the parent or family member going on. We work with both the buyer and the supporting borrower from the first conversation through to completion, and we do it all fee-free.
FAQs
What is a JBSP mortgage?
A Joint Borrower Sole Proprietor mortgage is a mortgage where more than one person is named on the application and shares responsibility for the repayments, but only one person owns the property and is named on the title deeds. The supporting borrower joins the application to boost affordability, without taking ownership of the property.
How is a JBSP different from a guarantor mortgage?
A guarantor mortgage sat outside the mortgage itself. The guarantor was a backup, only liable if the main borrower defaulted, often securing that with savings, an asset, or a charge against their own home. A JBSP puts the supporting borrower on the mortgage application from day one, with joint and several liability for the payments. JBSP has largely replaced traditional guarantor mortgages in the residential market.
Do parents pay the second home stamp duty surcharge on a JBSP?
No. The surcharge applies to people who go on the deeds of an additional property. On a JBSP, the supporting borrower is not on the deeds and has no ownership of the property, so the surcharge does not apply to them. Stamp duty is calculated on the main borrower's situation only.
Can siblings or in-laws go on a JBSP mortgage?
Often, yes. Most lenders prefer immediate family, but plenty will accept siblings, and we have arranged JBSP mortgages with in-laws involved. The exact eligibility varies by lender, but if there is a clear family relationship there is usually a route.
Does the supporting borrower need legal advice?
Yes. Lenders typically require the supporting borrower to take independent legal advice before completion, because they are taking on liability for the mortgage without gaining any ownership of the property. It is a standard part of the process.
Can the supporting borrower be removed from the mortgage later?
Usually yes, through a remortgage into the main borrower's sole name once their income alone supports the affordability. This is one of the more common reasons people use JBSP: it gets them onto the ladder now, with a clear route to take the mortgage on solo later.