Porting a mortgage in the UK: how does it work when you move?
A portable mortgage lets you apply to take an existing deal to a new property, but the move is still treated as a new lending decision.
If your mortgage is portable, you may be able to transfer the existing deal to a new property with the same lender. You still need to pass the lender’s current affordability and property checks. If you need extra borrowing, the additional amount may be on a different product. Porting can help avoid or reduce an early repayment charge, but the exact outcome depends on the lender and timing.
Portable does not mean automatic
Mortgage documents often describe a fixed or discounted deal as portable, but that is a feature of the product, not a promise that the lender must approve your next home. When you move, the lender reassesses income, commitments, credit position and the new property. If circumstances have changed materially, you can fail the new application even though the original mortgage has been paid perfectly.
Ask the lender for an early porting assessment before committing to a purchase. An agreement in principle or initial conversation is not a final mortgage offer, but it can reveal affordability problems while you still have options.
The existing balance and extra borrowing can be split
If the new home is more expensive, you may need to borrow more than the balance being ported. Lenders commonly keep the ported portion on the old product while placing the extra borrowing on a current product. That can leave two parts with different interest rates and end dates.
This split matters later. One portion may finish its fixed period before the other, making future remortgaging less tidy. Compare the long-term structure, not just whether the lender will lend the extra amount today.
Early repayment charges can influence the decision
If you sell and repay a fixed-rate mortgage before the deal ends, an early repayment charge may apply. Porting is often attractive because it can preserve the existing product and reduce or avoid that charge when the move fits the lender’s rules. Timing can be important where the sale and purchase do not complete together.
Some lenders refund an ERC if a customer repays and then completes a qualifying port within a defined period, while others structure the move differently. Check the mortgage offer and obtain the lender’s current porting rules in writing before assuming the charge will disappear.
The new property must be acceptable security
The lender assesses the new home as well as the borrower. A property with unusual construction, short lease, commercial use, valuation concerns or other risk can be unacceptable even when affordability is strong. Portability does not force the lender to accept any property you choose.
Arrange surveys and legal work with the mortgage timetable in mind. If the property fails the lender’s criteria late in the transaction, the financial consequences can include lost fees and the need to find a different lender quickly.
Compare porting with a full remortgage
Keeping a low existing fixed rate can be valuable, especially when current market rates are higher. But porting is not always cheapest. A new lender may offer a better overall package once you include product fees, ERCs, valuation costs and the interest rate on any additional borrowing.
Model both routes over a realistic period. If the difference is material or your circumstances are complex, regulated mortgage advice can be useful. The emotional appeal of “keeping my old rate” should not replace a full cost comparison.
Ask for the numbers in writing before exchanging contracts
Obtain the ported balance, interest rate, remaining product period, any extra borrowing rate, product fees and potential ERC in a form you can compare. If the sale and purchase may complete on different dates, ask how the lender treats the gap and whether any ERC refund has a deadline or conditions.
Property moves are expensive enough without assumptions. A written illustration lets your solicitor, broker and household understand the financing structure before you become legally committed to the purchase.
Porting can be particularly awkward when you move to a cheaper property. The lender may not allow the full old balance to remain if the new loan-to-value or borrowing need is lower, so part of the mortgage may be repaid and an ERC can potentially apply to that portion depending on the product rules. Ask the lender to illustrate a downsizing scenario separately from an upsizing one.
If your current deal is close to ending, porting may preserve a rate for only a short period before another product decision is due. Factor that timing into the move. Paying fees to preserve a deal with only a few months left can be less attractive than arranging a new mortgage structure that aligns all borrowing from the start.
Ask how the lender handles product fees on any additional borrowing and whether the extra part can later be switched without disturbing the ported part. Two sub-accounts can create two sets of future decisions, so understand the structure before accepting it.
Sources and verification
Isabelle Reed — Personal Finance Writer
I treat porting as a new mortgage application that happens to preserve an old product if the lender approves it. That mindset avoids the biggest misunderstanding: “portable” does not mean “guaranteed”. Income may have changed, the new property may not fit the lender’s criteria, and extra borrowing can create a second mortgage part on a different rate. Before making an offer on a home, I would ask the existing lender how much can be ported, what affordability it will test and how any early repayment charge works if the sale and purchase dates do not line up. Then I would compare that route with a complete remortgage, including fees and ERCs. Keeping an attractive old fixed rate can be excellent, but not if the extra borrowing is expensive or the split deal becomes awkward later. Porting should be a costed option, not an assumption built into the move. I would not exchange contracts based on a casual statement that the mortgage 'should port'. I want the lender’s actual offer and the ERC treatment clear, because timing mistakes can cost thousands. Downsizers should ask for a separate illustration because the amount that can actually be ported may be lower than the old balance, changing the ERC calculation.
MyBankAnswers uses official provider and UK regulatory sources wherever practical. Information is general and does not constitute financial advice.