Mortgage question
What is a JBSP (Joint Borrower Sole Proprietor) mortgage?
A Joint Borrower Sole Proprietor (JBSP) mortgage lets up to four people share the mortgage-repayment liability, boosting how much you can borrow, while only one or two people go on the property deed. Parents can join their child’s mortgage to help affordability without triggering the 5% additional-property Stamp Duty surcharge that a normal joint mortgage would. It has quietly become the dominant “bank of mum and dad” structure in 2026 — the main UK JBSP lenders include Barclays, Skipton, Clydesdale, Tipton & Coseley, Furness BS and Metro Bank.
What makes a JBSP different from a normal joint mortgage?
On a standard joint mortgage, all borrowers are on both the mortgage and the title deeds — they share the debt AND the ownership. If one of those borrowers already owns another property, HMRC treats this new purchase as an “additional property” and charges a 5% SDLT surcharge on every band (raised from 3% on 31 October 2024).
A JBSP separates the two. Up to four borrowers can sign the mortgage (making the income pot big enough for lenders), but only the child (or one or two named people) goes on the title. Because the parents don’t own the new home, no additional-property surcharge applies.
How does the SDLT saving actually work?
Concrete example. A 27-year-old first-time buyer buys a £300,000 flat with their parents’ help. The parents already own a home.
| Structure | SDLT payable |
|---|---|
| Solo purchase (FTB) | £0 (FTB relief up to £300k) |
| Joint mortgage + joint owners (parents on title, already own a home) | £18,500 (standard rates + 5% additional-property surcharge) |
| JBSP (parents on mortgage only, child on title as FTB) | £0 (FTB relief preserved) |
That’s £18,500 of SDLT avoided. On more expensive properties the gap widens further. See our stamp duty calculator to model your own numbers.
Who can be a JBSP helper — and what do they agree to?
Most lenders allow parents, step-parents, grandparents, aunts/uncles, adult siblings, and even close friends. The helper must:
- Pass the lender’s affordability test on their own income — their full income gets combined with the child’s for the sizing calculation.
- Accept “joint and several liability” — if the child can’t pay, the helper is legally liable for the full mortgage, not just their “share.”
- Be willing to stay on the mortgage for the agreed duration (some lenders offer a “staged release” that removes the helper after, say, 5 years if the child’s income has grown enough).
Credit checks apply to every borrower. A helper with recent defaults or CCJs can sink the application.
How much extra can you borrow?
Dramatic differences. A typical first-time buyer on £35,000 can borrow roughly £157,500 (4.5×). Add two parents earning a combined £60,000 each:
| Setup | Lender multiple | Borrowing power |
|---|---|---|
| Child alone on £35k | 4.5× | £157,500 |
| Joint mortgage with one parent on £60k | 4.5× on combined £95k | £427,500 |
| JBSP with both parents (combined £120k) | 4.5× on combined £155k | £697,500 |
Most lenders cap JBSP at four borrowers and typically restrict the helper’s income contribution to before their retirement age, so an older parent gets less credit. Use our affordability calculator to see your realistic number.
What are the trade-offs?
Not all upside:
- Helpers’ credit files show the debt. That impacts their own future borrowing (another mortgage, car finance, remortgage).
- Helpers have legal liability. If the child defaults, the lender will pursue the helper.
- No equity. Helpers don’t own the home — their name isn’t on the title — so they don’t benefit from price appreciation.
- Removal process. Coming off a JBSP requires a remortgage or formal transfer, and the child has to pass affordability solo at that point.
Some lenders (Barclays with their Family Springboard product, for example) combine JBSP with a parental deposit pledged in a linked savings account, earning interest for the parents in return for a deposit-free or low-deposit mortgage for the child.
The misconception worth clearing up
“A JBSP means parents own part of the house.” No — that’s what makes it work. Parents are on the mortgage but not on the deed, so legally they have no ownership stake. That preserves the child’s first-time buyer status, the FTB SDLT relief, and the absence of the 5% additional-property surcharge. If parents want ownership (for inheritance reasons, for example) they need a different structure — see joint tenants vs tenants in common. And because the helpers are legally liable for the whole debt, they should take independent legal advice before signing — the conveyancer will usually insist.
This is information, not regulated advice. A JBSP involves genuine tax and inheritance complexity — speak to a broker and a solicitor before committing.
Sources
Information, not regulated advice. Mortgage Notes is not an FCA-authorised mortgage adviser. For a recommendation on your specific circumstances, speak to an FCA-authorised broker.