Last reviewed: June 2026 | Source: GOV.UK and HM Revenue and Customs
TL;DR- A joint borrower sole proprietor mortgage, or JBSP, has more than one borrower but only one owner on the title.
- It is often used by parents helping an adult child borrow more while keeping the child as the sole owner.
- Because the helper is not on the title, the purchase can avoid the additional stamp duty surcharge that would apply if they were a co-owner who already owns property.
- Not all lenders offer JBSP, and criteria vary on who can be a supporting borrower.
- All borrowers are liable for the mortgage even though only one owns the property.
Key Facts
●Structure: Multiple borrowers, single owner on the title
●Common use: Parents helping an adult child buy
●Borrowing benefit: Helper's income can increase affordability
●Stamp duty point: Helper off the title can avoid the additional surcharge
●Liability: All borrowers are liable for the mortgage
●Availability: Offered by some lenders, with varying criteria
A joint borrower sole proprietor mortgage, usually shortened to JBSP, is a way for someone to borrow more by adding another person's income to the application without making that person a legal owner of the property. It is most commonly used by parents helping an adult child onto the property ladder. This guide explains how a JBSP works, who uses it, the important stamp duty implications, the liabilities involved, and which lenders tend to offer it.
How a JBSP mortgage works
A joint borrower sole proprietor mortgage involves more than one borrower on the mortgage but only one person named on the property's title deeds as the owner. The additional borrower, often a parent, supports the application with their income but does not become a legal owner of the home.
This separates the two roles that are normally combined in a standard joint mortgage, where the people on the mortgage are usually also the owners. In a JBSP, the supporting borrower helps the main applicant qualify for a larger loan while ownership rests solely with the main applicant.
The arrangement is designed to boost borrowing capacity. By adding the income of a supporting borrower, the lender can assess affordability on a larger combined income, which can allow the sole owner to borrow more than they could on their own.
Who uses a JBSP and why
The most common users are parents helping an adult child to buy a first home, where the child cannot borrow enough on their own income but the parents are willing to support the mortgage. The child becomes the sole owner, while the parents help with affordability as supporting borrowers.
It can also be used in other family situations, such as other relatives supporting a buyer, and occasionally beyond family depending on the lender. The key feature is that the supporting borrower wants to help with borrowing without taking an ownership stake in the property.
This appeals to families who want the buyer to be the sole owner, for personal, practical or tax reasons, while still providing the income support needed to secure the mortgage. It keeps ownership clearly with the intended buyer while making the purchase affordable.
The stamp duty advantage
A significant reason families choose a JBSP relates to stamp duty. Where someone already owns a property, buying an additional residential property as a co-owner can trigger the additional stamp duty surcharge that applies to second properties. In a JBSP, the supporting borrower is not on the title, so they are not a purchaser of the property.
Because the helper is not acquiring an ownership interest, the purchase can avoid the additional surcharge that would apply if a parent who already owns their own home were added as a joint owner. The sole proprietor is the only purchaser, and their stamp duty position is assessed accordingly.
This can make a JBSP more attractive than a standard joint mortgage where a property-owning parent would otherwise become a co-owner and bring the surcharge into play. The exact stamp duty treatment depends on the circumstances, so families should confirm the position with a conveyancer.
Liabilities and responsibilities
Although only one person owns the property, all the borrowers on a JBSP are liable for the mortgage. This means the supporting borrower is responsible for the loan alongside the owner, and a missed payment can affect all the borrowers, including the supporting borrower's credit record.
The supporting borrower takes on a real financial commitment without gaining ownership of the property, so they should understand the obligation clearly before entering into the arrangement. If the owner cannot pay, the lender can look to the supporting borrower for the debt.
Because of this imbalance between liability and ownership, families considering a JBSP should think carefully about the responsibilities involved and may wish to take legal advice. Being clear about who is liable for what, and what happens if circumstances change, helps avoid disputes later.
Lenders and criteria
Not all lenders offer joint borrower sole proprietor mortgages, and those that do set their own criteria on matters such as who can be a supporting borrower, the maximum number of borrowers, and how the supporting borrower's age and income are treated. Some focus on parent-and-child arrangements, while others are broader.
Lenders may also consider the supporting borrower's existing commitments and how long the support is expected to last, particularly where the supporting borrower is older. These criteria affect both whether a JBSP is available and how much can be borrowed.
Because availability and criteria vary, finding a suitable lender is an important step, and a mortgage broker can help identify those offering JBSP on terms that fit the family's situation. Matching the arrangement to a lender's criteria is central to making it work.
Comparing JBSP with other options
A JBSP is one of several ways families help relatives buy, alongside options such as gifting a deposit, acting as a guarantor, or taking a standard joint mortgage with joint ownership. Each option has different implications for ownership, liability and stamp duty.
Compared with a standard joint mortgage, a JBSP keeps the supporting borrower off the title, which is what allows the stamp duty surcharge to be avoided where the helper already owns property, while still adding their income for affordability. Compared with gifting a deposit, it provides ongoing income support rather than a one-off sum.
The right choice depends on the family's circumstances, including tax, the amount of help needed and how the parties want ownership to be structured. Because the options differ in important ways, taking mortgage and, where relevant, legal advice helps a family choose the approach that best fits their needs.
Frequently Asked Questions
What is a joint borrower sole proprietor mortgage?
A joint borrower sole proprietor mortgage, or JBSP, has more than one borrower on the mortgage but only one person named on the property's title deeds as the owner. The additional borrower, often a parent, supports the application with their income but does not become a legal owner. This boosts borrowing capacity, allowing the sole owner to borrow more than they could on their own income, while ownership rests entirely with the main applicant.
Why does a JBSP help with stamp duty?
Where someone already owns a property, becoming a co-owner of an additional residential property can trigger the additional stamp duty surcharge for second properties. In a JBSP, the supporting borrower is not on the title and so is not a purchaser, which means the purchase can avoid that surcharge that would apply if, for example, a property-owning parent were added as a joint owner. The exact treatment depends on the circumstances, so confirm with a conveyancer.
Who is liable for a JBSP mortgage?
All the borrowers on a JBSP are liable for the mortgage, even though only one person owns the property. This means the supporting borrower is responsible for the loan alongside the owner, and a missed payment can affect everyone, including the supporting borrower's credit record. The supporting borrower takes on a real financial commitment without gaining ownership, so they should understand the obligation clearly and may wish to take legal advice before proceeding.
Which lenders offer JBSP mortgages?
Not all lenders offer joint borrower sole proprietor mortgages, and those that do set their own criteria on who can be a supporting borrower, the number of borrowers, and how the supporting borrower's age and income are treated. Some focus on parent-and-child arrangements while others are broader. Because availability and criteria vary, a mortgage broker can help identify lenders offering JBSP on terms that fit the family's situation.
