Last reviewed: June 2026
TL;DR- Adding someone to a mortgage is called a transfer of equity - the new person is added to the legal title and the mortgage simultaneously.
- Lender consent is required and a new affordability assessment is carried out including the new borrower's income and credit history.
- Stamp duty land tax may apply on the transaction depending on the consideration paid and whether the new borrower has other properties.
- A solicitor is required to handle the transfer of equity and register the change at HM Land Registry.
What Is a Transfer of Equity?
Adding someone to an existing mortgage is legally a transfer of equity - a change to the legal ownership of the property and the mortgage. The existing owner transfers a share of their ownership to the new person. The new person typically also joins the mortgage as a joint borrower, sharing liability for the debt. A solicitor must carry out the legal work and register the change at HM Land Registry.
This process is used when: a couple moves in together and wants to formalise joint ownership; a parent wants to add an adult child; or a business partner or friend is joining as a co-owner. It is also used when one person is being added to provide additional income for affordability purposes (joint borrower sole proprietor).
The Lender's Role
The existing lender must consent to the transfer of equity. The lender assesses whether the new joint borrower's inclusion is acceptable: a new affordability assessment is typically carried out on the combined income and outgoings of all borrowers; the new person's credit history is assessed; and the lender must be satisfied that the mortgage remains affordable with the changed ownership structure. If the existing mortgage is within a fixed rate deal period, porting considerations apply - adding a borrower may trigger a full remortgage in some cases.
Stamp Duty on Transfer of Equity
Adding someone to a mortgage involves a transfer of equity. If consideration (money) passes - for example, the new person pays for their share - SDLT may apply on the consideration. The exact SDLT treatment depends on the specific transaction structure. If the new person has other properties, the additional dwelling surcharge may apply. Specialist conveyancing and tax advice should be taken before proceeding, as the SDLT position on transfers of equity can be complex.
Joint Borrower Sole Proprietor
An alternative to a full joint ownership structure is the joint borrower sole proprietor (JBSP) arrangement, where a family member is added to the mortgage as a borrower (increasing the income assessed for affordability) but is not added to the property title (and therefore does not appear as an owner). The existing owner remains the sole legal owner. This avoids SDLT issues for the additional borrower but means they have mortgage liability without ownership rights. Not all lenders offer JBSP arrangements and specific criteria vary.
Frequently Asked Questions
Does adding someone to a mortgage affect the existing deal?
In most cases, adding a borrower during a fixed rate deal period is treated as a remortgage by the lender, which may trigger an ERC. Some lenders allow a borrower to be added via a product transfer without triggering an ERC. The lender's specific policy on this should be checked before proceeding. Where an ERC would apply, it may be more cost-effective to wait until the deal period ends.
Can I add someone without going through a solicitor?
No. A transfer of equity requires legal work to amend the title deeds at HM Land Registry and to update the mortgage documentation. A solicitor or licensed conveyancer must be instructed. The cost of conveyancing for a transfer of equity is typically £500-£1,500 plus disbursements.
What credit score does the new borrower need?
The new borrower must meet the lender's standard credit criteria. Adverse credit history will affect the application in the same way as for a new mortgage application. The lender's automated scoring or underwriting will assess the new borrower's credit file as part of the consent process. If the new borrower has adverse credit that would prevent the application being accepted, the transfer of equity cannot proceed with that lender.
Can I add someone to a buy-to-let mortgage?
Yes, in principle, though the process is the same as for residential transfers of equity: lender consent required, new assessment (in this case primarily rental coverage), solicitor required, SDLT potentially applicable. Some BTL lenders restrict who can be added as a joint BTL borrower. Specialist advice should be sought for BTL transfer of equity transactions.
