What is a Joint Borrower Sole Proprietor Mortgage (JBSP)?
A joint borrower sole proprietor mortgage (often shortened to JBSP) lets you bring someone else onto your mortgage application to boost your affordability and borrow more, without them becoming an owner of the property.
They go on the mortgage, but not on the deeds: you remain the sole proprietor, and the property is entirely yours.
Most commonly it’s a parent joining a child’s application to help them onto the ladder. But we’ve also seen siblings, friends and even couples use this arrangement. Everyone on the mortgage is jointly liable for the payments, but only you own the home.
What’s the criteria for a JBSP mortgage?
Every lender is different, but here’s what to expect with a JBSP application:
- Affordability — both incomes are used, but so are both sets of outgoings. If your supporting borrower has a mortgage on their own home, lenders will account for that in their assessment
- Maximum age — normally 75–80 at the end of the mortgage term, based on the oldest applicant. This can shorten the available term when a parent joins the application
- Deposit — JBSP mortgages can go up to 95% loan-to-value, so a 5% deposit can be enough
- Number of applicants — up to 4 in total, with some lenders using all four incomes
- Credit score — all applicants must meet the lender’s credit requirements, not just the buyer
- Relationship — most lenders require the joint borrower to be a family member, though a few will also accept friends
- Repayment type — JBSP mortgages must be on capital repayment, not interest-only
- Standard criteria — all applicants must meet the lender’s usual requirements too
As ever, criteria vary from one lender to the next, and matching your circumstances to the right one is exactly what we do.
What should the joint borrower consider?
A JBSP mortgage is a generous thing to do, and it’s important the supporting borrower goes in with eyes open.
They’ll be fully liable for the mortgage payments if the owner can’t pay, and the commitment will appear as an outgoing on their credit file, which can affect any future borrowing of their own. And because they’re not on the deeds, they have no ownership of the property or claim to its equity.
The good news is that a JBSP arrangement doesn’t have to be forever. Once your income has grown, it’s often possible to remove the supporting borrower by remortgaging in your sole name, which is something we can help with when the time comes.
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How does stamp duty work with a JBSP mortgage?
This is where a JBSP mortgage can be beneficial. Because your supporting borrower isn’t registered as an owner, stamp duty is assessed on your circumstances alone.
That has two big advantages. If you’re a first-time buyer, you keep your first-time buyer stamp duty relief in England and Northern Ireland, even if the parent helping you already owns a home. And your supporting borrower won’t trigger the additional-property surcharge that would normally apply if a homeowner were added to the deeds.
It’s a tax-efficient way for family to help, and one of the main reasons buyers choose JBSP over a standard joint mortgage.
Independent legal advice for each borrower
One requirement to be aware of is that all supporting borrowers must obtain independent legal advice before completion. This is there to protect them — it confirms they understand they’re taking on full responsibility for a mortgage on a property they won’t own. It’s a standard part of the process, and we’ll help you factor it into your timeline and budget from the start.
Why use Mortgage Synergy?
Not every lender offers JBSP mortgages, and among those that do, criteria on age, relationship and the number of applicants vary considerably. Rates are typically in line with standard mortgage products, but finding the right lender for your family’s circumstances takes market knowledge.
As independent, FCA-regulated mortgage advisers with access to lenders across the whole UK market, we know exactly who offers JBSP, what they’ll accept, and how to structure your application. We’ll break down the jargon, coordinate the legal advice requirements, and guide both you and your supporting borrowers through every step.
Ready to get started?
If you’re thinking a helping hand could get you the home you want, we’d love to talk it through. Tell us about your mortgage requirements and one of our specialist advisers will be in touch within 24 hours.
Your home may be repossessed if you do not keep up repayments on your mortgage.
Joint Borrower Sole Proprietor Mortgage FAQs
A good number of high street banks, building societies and specialist lenders offer JBSP. However, each has its own rules on maximum age, who can act as a joint borrower and how many applicants they’ll accept. As whole-of-market advisers, we’ll match you with the lender whose criteria fit your family’s situation, rather than you approaching banks one by one.
Most lenders require the mortgage to end by the time the oldest applicant reaches around 75–80. Because the limit works off the oldest borrower, a parent joining the application can shorten the maximum term. We’ll factor this into your affordability calculations from the outset.
No. Stamp duty falls to the owner of the property, and the joint borrower isn’t an owner. That means no additional-property surcharge for a parent who owns their own home, and the buyer keeps any first-time buyer relief they’re entitled to.
No, not in a JBSP arrangement. The whole point is that they’re a borrower, not an owner. If they were added to the deeds, the stamp duty position would change and the arrangement would become a standard joint mortgage.
Often, yes. Once the owner’s income has grown enough to pass the lender’s affordability assessment alone, the supporting borrower can usually be removed by remortgaging.
No. A guarantor only steps in if payments are missed, and usually secures the promise against their own home or savings. With JBSP, the supporting borrower is on the mortgage itself from day one and jointly responsible for every payment, which is why lenders will use their income to boost what you can borrow.
Yes, some lenders will accept a partner as the joint borrower. It can suit couples where one of you already owns a property and would trigger the additional-property surcharge if added to the deeds, or where only one of you qualifies for first-time buyer relief. Bear in mind the supporting partner won’t own the home or have a claim to its equity, so it’s worth getting advice on whether JBSP or a standard joint mortgage is the better arrangement for you both.