A joint borrower sole proprietor (JBSP) mortgage lets you add up to three other people's incomes to your mortgage application to increase how much you can borrow, without making them legal owners of the property. It's commonly used by parents helping a child buy their first home, but the same structure can work between siblings, partners or friends too.
Key takeaway: With a JBSP mortgage, everyone named on the application is responsible for the monthly repayments, but only the person (or people) named as proprietor owns the property and appears on the title deeds. Not every lender offers this, and the ones that do vary significantly on how many applicants they'll accept and up to what age. It's also not the only way to boost your borrowing, so it's worth checking whether you actually need it.
[[stats: Up to 4 = Applicants some lenders will consider | 85 = Oldest maximum age limit available | 90+ = Lenders we search across the market | 0% = Ownership required from a supporting borrower]]
What is a joint borrower sole proprietor mortgage?
On a standard joint mortgage, everyone named on the application is also a legal owner of the property. A JBSP mortgage works differently: it separates who's financially responsible for the mortgage from who actually owns the home.
The person (or people) who will live in the property and own it are the proprietor(s). Anyone else added purely to boost affordability is a non-proprietor borrower, sometimes called a supporter or sponsor. Non-proprietor borrowers are jointly and severally liable for the full mortgage debt from day one, not just a fallback if payments are missed, but they don't appear on the title deeds and typically won't pay Stamp Duty or Land Transaction Tax as a result. Lenders that offer JBSP mortgages require every non-proprietor borrower to take independent legal advice before completion, so they understand exactly what they're taking on.
How is a JBSP mortgage different from a guarantor mortgage?
The two are often confused, but they work quite differently.
[[table: | Guarantor mortgage | JBSP mortgage ;; When are they liable? | Only if the main borrower misses a payment | Jointly liable for the full mortgage from the first payment ;; Do they own the property? | No | No ;; Do they usually offer their own property or savings as security? | Often, yes | No ;; Is independent legal advice required? | Sometimes | Yes, in every case]]
If you haven't started your first mortgage application yet, our guide on how to prepare to buy your first property covers the basics, and getting an Agreement in Principle early is a sensible first step whether or not you end up needing a JBSP arrangement.
Who is a JBSP mortgage useful for?
- First-time buyers whose own income doesn't quite stretch far enough, where a parent or family member's income can close the gap.
- Adult children supporting a parent - some lenders have widened their JBSP criteria so the arrangement can work in either direction, not just older generations supporting younger ones.
- Couples or partners where one person has a lower income or a less established credit history and isn't ready to be a legal co-owner yet.
- Friends buying together where only one person wants to be the legal owner, though most lenders restrict non-proprietor borrowers to close family members, so this is far less widely available.
Curious how combining incomes could change what you might be able to borrow? Try the calculator below.
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Do you actually need a JBSP mortgage?
JBSP isn't the only way to increase what you can borrow, and it's worth ruling out simpler options first, since adding a non-proprietor borrower means someone else takes on real liability for your mortgage. Some lenders instead offer enhanced income multiples to first-time buyers, which can close the same affordability gap using only your own income, without a second person needing to apply at all.
Nationwide's Helping Hand scheme is a good example: it isn't a JBSP product, but it lets eligible first-time buyers borrow up to 6 times their income instead of the more typical 4 to 4.5 times, provided they meet minimum income and other criteria. A number of lenders offer similar enhanced-multiple schemes for first-time buyers, and which ones are available, and on what terms, changes regularly through 2026.
If an enhanced-multiple lender gets you to the figure you need using only your own income, it's usually the simpler route: no non-proprietor borrower, no independent legal advice for a third party, and no complications if you want to restructure the mortgage later. JBSP tends to make more sense once you've ruled out enhanced multiples, or where a family member's income needs to be brought in regardless. Speak to Quanstrom Financial and we'll check both routes before recommending either.
Which lenders offer JBSP mortgages?
Not every lender offers a JBSP mortgage, and among those that do, policies vary considerably on applicant numbers, age limits and who qualifies as a supporter. Here's how six lenders currently compare.
[[table: Lender | Do they offer JBSP? | How many applicants do they allow? | Maximum age limit ;; Skipton Building Society (Income Booster) | Yes | Up to 4 | Up to 80, where the main applicant's income is equal to or less than 6.5x the loan requested ;; Barclays (Mortgage Boost) | Yes | Up to 4, though only the highest 2 incomes count towards affordability | Mortgage term can't extend beyond any applicant's 80th birthday ;; Metro Bank | Yes | Up to 4 | 80 ;; Principality Building Society (Family Boosts) | Yes, close family members only | Up to 4 | Up to 85 ;; NatWest (Family-Backed Mortgage) | Yes | 2 (the owner plus one non-owner) | 75 ;; Generation Home (Gen H) | Yes | Up to 4, with all 4 incomes considered | No fixed maximum for the supporting borrower, subject to the owner-occupier's own income]]
Maximum loan-to-value varies too. Metro Bank can lend up to 100% LTV on a JBSP application where all borrowers are immediate family, while most other lenders offering JBSP cap borrowing at around 95% LTV.
Tip: Lender appetite and criteria on JBSP mortgages change frequently, and this isn't every lender in the market. Speak to Quanstrom Financial to find out which lenders, or which alternative scheme, would suit your circumstances.
What do you need to apply?
- Income evidence for every applicant - payslips and tax documents as usual. If any applicant is self-employed, lenders will want the same evidence as any other self-employed mortgage application.
- A credit check for everyone named - all applicants are credit scored, since everyone is financially responsible for the mortgage.
- Independent legal advice for each non-proprietor borrower, confirming they understand the arrangement before completion.
- Clarity on who'll live in the property - this varies by lender. Some require only the proprietor to reside there, but with many lenders the non-proprietor borrower is welcome to live in the property too, so check what your chosen lender allows.
Can a supporter be removed later?
Usually, yes, though it isn't automatic. As the proprietor's income grows or the mortgage balance reduces, they may be able to remortgage or complete a product transfer in their sole name once they meet the lender's standard affordability requirements on their own. The non-proprietor's solicitor would then remove the legal charge from the property. This isn't guaranteed and depends on affordability at the time, so it's worth treating a JBSP mortgage as a step towards sole ownership rather than a permanent arrangement.
What are the risks to weigh up?
- Full liability, not just a fallback - a non-proprietor borrower is responsible for the whole mortgage debt, not only stepping in if payments are missed.
- It shows on the supporter's credit file - which can affect their own ability to borrow for a mortgage or other credit in future.
- It's a long-term commitment - most lenders base the mortgage term on the oldest applicant, which can mean a shorter term and higher monthly payments than the proprietor might manage alone.
- Relationships can be tested - it's worth agreeing expectations with everyone involved before applying, ideally in writing alongside the independent legal advice.
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Frequently asked questions
Does a JBSP mortgage affect the supporting person's credit score?
Yes. The mortgage is held jointly, so it appears on the supporting borrower's credit report as well as the proprietor's, and applying involves a full credit check for everyone named.
Can a JBSP mortgage be used to buy a new build home?
Generally, yes, though some lenders restrict combining a JBSP mortgage with other new build incentive schemes. Our guide to new build mortgages for first-time buyers covers what else to check.
Is a JBSP mortgage the same as a joint mortgage?
No. On a standard joint mortgage, everyone named is also a legal owner of the property. On a JBSP mortgage, only the proprietor(s) own the property, even though all applicants are financially responsible for the repayments.
Does the supporting borrower pay Stamp Duty?
Because the non-proprietor borrower isn't named on the title deeds, they generally aren't treated as a buyer for Stamp Duty purposes, and the proprietor's own first-time buyer status is usually what determines any relief available.
Can a supporter be removed from a JBSP mortgage later?
Often, yes, once the proprietor can meet the lender's standard affordability requirements alone, though this depends on their circumstances and the lender's criteria at the time rather than being guaranteed.
Written by Toby Quanstrom CeMAP, Director at Quanstrom Financial, a whole-of-market mortgage broker based in Eastbourne, East Sussex.
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