Mortgage porting in the UK: costs, checks and timing
Porting a mortgage means applying to take an existing mortgage product to a new property, not simply moving the old loan automatically. The lender normally reassesses affordability and the new property, and any extra borrowing may sit on a separate product with a different rate and end date.
Before relying on porting, ask the lender for a written illustration showing the balance that can stay on the existing deal, any additional borrowing, fees, early repayment charges and monthly payments. Then compare that package with a full remortgage.
Confirm that porting is available and affordable now
MoneyHelper says most mortgages are portable, but porting is still treated as a new mortgage application. You must meet the lender’s current affordability and other criteria, and the new property must be acceptable security. A mortgage that was affordable five years ago is not automatically approved again after income, debts or lending rules have changed.
Get an early indication before committing to a purchase. If the lender refuses the port after you have agreed a sale and purchase, you may have to find another mortgage and potentially pay an early repayment charge on the old deal.
Ask for the lender porting rules before treating the existing mortgage as portable in practice. Record the current balance, remaining fixed period, proposed purchase price and extra borrowing required. Porting normally still depends on a fresh lending decision and an acceptable new property, so a portable product is not the same as guaranteed approval.
Worked checkpoint: put the decision on one line before acting. For porting a mortgage, use an example amount such as £1,265 and write down the date the money is needed, every visible fee or charge, and the alternative if the preferred route fails. Then compare the final pounds paid or received rather than one headline rate. This makes it easier to notice when a small percentage, an early-repayment charge, a notice period or a conversion choice changes the real outcome. Keep the calculation with the account message or quote so you can revisit the decision later.
Calculate the cost of extra borrowing and any ERC
Suppose you owe £180,000 on a 2.2% fixed deal and need a £260,000 mortgage for the new home. The lender may allow the £180,000 to remain on the old product while the extra £80,000 is borrowed on a current product. Those two parts can have different rates and fixed-end dates.
That split can be valuable if the old rate is attractive, but it can also create future complexity. When the £180,000 part ends, the £80,000 part may still be tied in with an ERC, making it harder to refinance the whole mortgage together.
If the sale repays the old mortgage before the port completes, the lender’s rules determine whether an ERC is charged and whether it can later be refunded if the new mortgage completes within a specified period. Do not assume every lender handles the gap the same way.
On a £200,000 balance, a 2% ERC is £4,000. That is large enough to change whether porting, waiting, or remortgaging elsewhere is financially sensible. Ask for the exact charge for your proposed dates.
Calculate the split loan rather than focusing only on the attractive old rate. If £180,000 stays on an older product and £80,000 is new borrowing, compare the monthly payment and end date of each part. Then add fees and any early repayment charge that could arise if the sale and purchase do not line up as expected.
Worked checkpoint: put the decision on one line before acting. For porting a mortgage, use an example amount such as £1,536 and write down the date the money is needed, every visible fee or charge, and the alternative if the preferred route fails. Then compare the final pounds paid or received rather than one headline rate. This makes it easier to notice when a small percentage, an early-repayment charge, a notice period or a conversion choice changes the real outcome. Keep the calculation with the account message or quote so you can revisit the decision later.
Check the new property and the timing of both transactions
Porting preserves a product, not an approval of the new home. The lender can reject a property because of valuation, construction, lease terms, location or other lending criteria. A more expensive property can also change the loan-to-value ratio and therefore the available top-up products.
If you are buying an unusual property, raise that early. The cheapest outcome on paper is irrelevant if the lender will not accept the property as security.
Keeping £150,000 at 2% sounds compelling, but if another £150,000 is borrowed at 5.5%, fees are high and the two deals end at awkward times, the overall package may be less attractive than a single new mortgage. Calculate the weighted cost and total fees over the period you expect to keep the loan.
Ask the lender or broker to show the monthly payment for each sub-account and the total. Then compare the full remortgage alternative on the same time horizon.
Put the transaction dates on one timeline: sale completion, purchase completion, old fixed-rate end date and any lender deadline for an ERC refund or port. Ask the lender or broker what happens if the transactions are not simultaneous. A timing mismatch of even a few weeks can materially change the cash needed at completion.
Worked checkpoint: put the decision on one line before acting. For porting a mortgage, use an example amount such as £1,807 and write down the date the money is needed, every visible fee or charge, and the alternative if the preferred route fails. Then compare the final pounds paid or received rather than one headline rate. This makes it easier to notice when a small percentage, an early-repayment charge, a notice period or a conversion choice changes the real outcome. Keep the calculation with the account message or quote so you can revisit the decision later.
Compare the whole package before committing
The practical risks are often timing and flexibility. Selling and buying on different dates, needing much more borrowing, or planning another move soon can make a theoretically portable mortgage awkward. Build those facts into the decision before exchange of contracts.
Get the lender’s porting rules, ERC treatment and additional-borrowing options in writing. “This mortgage is portable” is only the starting point; the useful question is what porting will cost and whether the lender will approve your specific move.
Does porting mean I keep the same mortgage automatically?
No. You normally make a new mortgage application and must pass current affordability and property checks.
What happens if I need to borrow more?
The additional amount may be placed on a separate current product, which can have a different rate and end date.
Can porting avoid an early repayment charge?
Sometimes, but the lender’s timing and porting rules matter. Ask for the exact ERC treatment for your sale and purchase dates.
Compare porting with a full remortgage over the same time horizon. Include the blended interest cost, valuation or legal fees, product fees, ERCs and the flexibility cost of having two sub-accounts with different end dates. The cheapest-looking rate is not necessarily the cheaper or easier mortgage package.
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.