Not every buyer can qualify for the mortgage they need on their own income and deposit alone. Guarantor and joint mortgages offer two different routes to bridging that gap — each with real benefits, but also real risks that every party should understand before signing.
Joint mortgages: borrowing together
A joint mortgage simply means two (or occasionally more) people apply together, combining incomes to increase borrowing capacity and jointly owning the property. This is the standard arrangement for most couples buying together, but joint mortgages can also involve friends, siblings, or parent-and-child combinations.
Guarantor mortgages: a helping hand without joint ownership
A guarantor mortgage allows a family member (commonly a parent) to guarantee the mortgage payments — often by offering their own property or savings as security, or simply agreeing to cover payments if the main borrower can't — without necessarily being named on the property's title or taking an ownership share. This can help buyers with a limited income or credit history qualify for a mortgage they couldn't get alone.
How a guarantor's commitment works
- Income-backed guarantee: The guarantor's income is used to support the affordability assessment, without necessarily providing security.
- Savings-backed guarantee: The guarantor deposits savings with the lender as security, sometimes earning interest, released once the mortgage reaches a certain loan-to-value or after a set period.
- Property-backed guarantee: The guarantor offers equity in their own property as additional security — the highest-risk option for the guarantor, since their own home could ultimately be at risk if the mortgage isn't repaid.
Joint Borrower Sole Proprietor mortgages
A increasingly popular hybrid is the Joint Borrower Sole Proprietor (JBSP) mortgage: a family member's income supports the mortgage application (increasing what can be borrowed), but only the actual buyer is named on the property title. This avoids some of the complications of full joint ownership — such as Stamp Duty surcharges that can apply to additional-property owners — while still boosting affordability.
Risks every guarantor should understand
- You are potentially liable for someone else's mortgage debt if they can't pay — this can affect your own credit file and finances significantly.
- Property or savings offered as security could be at risk in a worst-case scenario.
- Being a guarantor may affect your own ability to borrow in future, since lenders will usually factor in the contingent liability.
- Family relationships can be strained if repayment issues arise — a written agreement between all parties, ideally reviewed by a solicitor, is strongly advisable even among close family.
How to exit a guarantor or joint arrangement later
Most guarantor arrangements include a review point — often once the mortgage reaches a certain loan-to-value, or after a fixed number of years — at which the main borrower may be able to remortgage in their own name, releasing the guarantor from their commitment. Joint mortgages can potentially be restructured into a sole name mortgage later, subject to the remaining borrower qualifying for the mortgage independently and the lender's consent (or via remortgaging to a new lender).
Worth reading next: our guide on Mortgages for the Self-Employed: A Practical Guide, and How Much Deposit Do You Need for a UK Mortgage?.
Our free Mortgage Affordability Calculator can help you check this against your own figures.
The bottom line
Guarantor and joint mortgages can be genuinely effective ways to help buyers onto the property ladder sooner than they could manage alone, but they create real financial and legal ties between the parties involved. Anyone considering acting as a guarantor, in particular, should seek independent advice and fully understand the worst-case scenario before agreeing.