Key Facts
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- Sources: FCA, gov.uk, HMRC, Money and Pensions Service
- Last reviewed June 2026
What Is Porting a Mortgage?
Porting a mortgage means transferring your existing mortgage - its rate, terms, and outstanding balance - from the property being sold to the new property being purchased. Porting a mortgage allows borrowers to keep their current interest rate and avoid paying an early repayment charge when moving home.
Most fixed-rate and tracker mortgage products are portable in principle, meaning the lender allows the transfer subject to a new application and approval process on the new property. However, portability is at the lender's discretion - they are not legally obligated to agree to porting a mortgage even if the product documentation describes it as portable.
Porting a mortgage does not mean the mortgage automatically transfers. The borrower must apply to port, the lender assesses the new property and the borrower's current financial circumstances, and the lender decides whether to approve the port. A declined porting application means the ERC may still apply.
How Porting a Mortgage Works
Porting a mortgage involves two simultaneous transactions: redeeming the existing mortgage on the property being sold and creating a new mortgage on the property being purchased on the same rate and terms. The lender treats this as a continuation of the existing facility rather than a new mortgage.
The process requires a new affordability assessment based on current circumstances - income, outgoings, and credit history at the time of porting, not at the time the original mortgage was taken out. Changes in income, new credit commitments, or changes in the lender's underwriting criteria since the original mortgage was issued can result in a porting application being declined even if the product is described as portable.
Timing is critical when porting a mortgage. The completion of the sale and purchase must be simultaneous, or at least within the lender's permitted overlap period (typically a few weeks). If the sale completes before the purchase, the mortgage is redeemed and cannot be ported - the borrower must apply for a new mortgage.
Porting a Mortgage When Borrowing More
If the new property costs more than the property being sold, the borrower needs to borrow more than the current outstanding mortgage balance. In this case, porting a mortgage involves retaining the existing rate on the ported balance and taking an additional top-up mortgage at a new rate for the extra amount.
The two-rate structure that results from porting a mortgage with a top-up can be administratively complex and may not produce the most competitive overall rate. The top-up mortgage is typically on the lender's current product range at the time of porting, which may be at a significantly different rate from the ported mortgage.
Borrowers should compare the total cost of porting a mortgage plus a top-up against the alternative of paying the ERC and remortgaging entirely to the most competitive rate available. If the ERC is large and the ported rate is significantly lower than current rates, porting a mortgage even with a two-rate structure typically saves money overall.
When Porting a Mortgage Does Not Make Sense
Porting a mortgage is most valuable when the existing rate is materially lower than current market rates and the ERC is significant. If mortgage rates have fallen since the existing deal was taken out, porting a mortgage to keep a higher rate may be counterproductive - paying the ERC and remortgaging to a lower rate might produce a better outcome.
If the lender's current products are significantly better than the ported rate, porting a mortgage at the old rate foregoes the saving available from the current market. Borrowers should compare the total cost over the remaining fixed period of: (a) porting at the existing rate, (b) paying the ERC and remortgaging at the best current rate, and (c) porting the existing balance and taking a competitive top-up.
If the new property is in a different location that the lender does not serve, or is of a property type the lender does not accept, porting a mortgage may not be technically possible regardless of the rate advantage. Confirming the new property meets the lender's criteria before committing to a purchase is an important early step.
How to Apply to Port a Mortgage
The process of porting a mortgage begins with notifying the existing lender of the intended sale and purchase as early as possible. Most lenders have a specific porting application process that runs alongside the standard property transaction.
The borrower submits a new mortgage application to the existing lender for the new property, including current income documentation, bank statements, and details of the new property. The lender assesses the application, arranges a valuation of the new property, and issues a new mortgage offer on the ported terms if the application is approved.
A mortgage broker can manage the porting a mortgage application alongside the overall transaction, coordinating with the solicitor and lender to ensure the timing aligns. In complex chain transactions, the broker's management of the porting process is particularly valuable in preventing timing mismatches that would result in the mortgage being redeemed rather than ported.
Porting a Mortgage vs Remortgaging to a New Lender
The decision between porting a mortgage and remortgaging to a new lender comes down to comparing the total cost of each option over the remaining deal period. Porting avoids the ERC but retains the existing rate. Remortgaging pays the ERC but accesses potentially better rates from the full market.
For a borrower three years into a five-year fix at 2 percent with an ERC of 2 percent and current rates at 4.5 percent, porting the mortgage saves the ERC and retains the very low rate for the remaining two years - almost certainly the better option. For a borrower one year into a two-year fix at 5.5 percent with current rates at 4 percent, paying the ERC to access the lower rate may produce a better outcome over the remaining period.
The calculation is specific to each situation and should be modelled with actual figures. A mortgage broker can run the comparison in minutes and identify the optimal approach, including the option of porting the existing balance at the old rate while taking an additional top-up at a new competitive rate.
Disclaimer: This guide is for informational purposes only and does not constitute financial advice. Products, eligibility criteria and regulations change frequently. Consult an FCA-authorised adviser before making any decision. Kael Tripton Ltd is not authorised or regulated by the Financial Conduct Authority.
Frequently Asked Questions
What does porting a mortgage mean?
Porting a mortgage means transferring your existing mortgage rate and terms to a new property when you move. It avoids paying an early repayment charge on the current deal and is subject to the lender approving a new application on the new property.
Is porting a mortgage always possible?
No. Portability is at the lender's discretion. A new affordability assessment and property valuation are required. Changed circumstances, different property type, or tightened lender criteria since the original mortgage can result in a porting application being declined.
What happens if I need to borrow more when porting?
If the new property costs more than the existing one, the ported balance keeps the existing rate and an additional top-up mortgage is arranged at the lender's current rate. The result is two mortgage components at different rates.
Does porting a mortgage affect my credit score?
The new affordability assessment for porting involves a credit check, which has a minor temporary impact on the credit score. This is equivalent to any standard mortgage application.
What if porting my mortgage is declined?
If porting is declined, the existing mortgage must be redeemed on sale of the current property and an ERC may apply. The borrower then applies for a new mortgage from any lender for the new purchase.
Sources
Last reviewed June 2026 · Kael Tripton Editorial
