Porting a mortgage when moving home can let you keep an existing fixed or discounted interest rate instead of replacing it with a new deal. For UK homeowners, this can be particularly valuable when the existing rate is lower than current offers. But portability does not guarantee approval, and moving may still involve affordability checks, property assessments, new fees and additional borrowing at a different rate.
The important decision is not simply whether your mortgage is portable. It is whether porting will leave you better off than taking out a new mortgage, after allowing for interest, early repayment charges, fees and the risks of your move falling through.
What does porting a mortgage actually mean?
Mortgage porting generally means transferring the interest rate and product terms associated with your existing mortgage to borrowing secured on your next home, subject to your lender's rules.
It does not usually mean that the original mortgage contract and its security automatically move unchanged from one property to another. Your old mortgage is typically redeemed when you sell, and a mortgage is arranged against the new property under the lender's porting process.
According to MoneyHelper's guidance on remortgaging and moving home, mortgage portability does not remove the need to satisfy the lender's applicable lending criteria. Porting can also become more complicated when you need additional borrowing.
Three important points are worth establishing before you make an offer on your next home:
- Portability is conditional. Your mortgage offer may describe a portable product without guaranteeing that a future application will succeed.
- Your existing rate may cover only the ported balance. Additional borrowing could require a separate product at a different rate.
- Timing matters. Selling and buying on different dates may affect early repayment charges and whether a later refund is available.
When is porting a mortgage worth considering?
Porting is particularly worth investigating if you have a competitive rate with significant time left on the deal, especially when leaving early would trigger a substantial early repayment charge (ERC).
For example, someone with a fixed rate of 2.5% and two years remaining may want to preserve that rate rather than replace all their borrowing with a higher-rate product.
However, porting can be less attractive if the deal is almost finished, your lender's additional borrowing is expensive, or another mortgage provides enough interest and fee savings to outweigh the cost of leaving.
| Situation | What to examine |
|---|---|
| Low existing rate with years remaining | Interest savings and ERC avoided through porting |
| Moving to a more expensive property | Additional borrowing rate and affordability |
| Moving to a cheaper property | Partial porting and possible ERC on repaid borrowing |
| Current deal almost finished | Whether a new mortgage is simpler or cheaper |
| Sale and purchase on different dates | Porting deadline, upfront ERC and refund conditions |
What costs can you face when porting a mortgage?
A successful port can avoid some costs associated with ending your existing deal, but it does not make moving home free.
1. Early repayment charges
An ERC is a charge that may apply if you repay mortgage borrowing during a period when early repayment restrictions apply. It is often expressed as a percentage of the relevant outstanding balance, although the exact calculation depends on your agreement.
For an illustrative example, a 3% ERC on a £180,000 balance would be:
£180,000 × 3% = £5,400.
That is a potential cost of leaving the deal, not necessarily a cost of porting. Successful porting may allow you to avoid it, subject to the lender's conditions.
If you sell before buying, some lenders require an ERC to be paid initially and refund it when an eligible new mortgage completes within a specified period. Other arrangements may work differently.
For example, Barclays' published porting information describes an arrangement under which the existing mortgage balance can be ported without an ERC if the new mortgage starts within 180 days of the sale. This is a Barclays-specific example, not a universal six-month rule.
Ask your own lender for its conditions in writing.
2. Mortgage product and arrangement fees
Even when you preserve your current deal, borrowing more may mean selecting a separate mortgage product with its own fee.
Compare both the interest rate and the cost of the product. A higher-rate deal with no arrangement fee may sometimes be cheaper over a short period than a lower-rate deal with a substantial upfront charge.
If your lender lets you add the fee to the mortgage, remember that you may pay interest on it. The trade-off between cash available at completion and longer-term borrowing costs is covered in our guide to paying mortgage arrangement fees upfront or adding them to the loan.
3. Valuation, legal and moving costs
Porting normally still involves a new property purchase, so you should budget for the usual relevant transaction costs.
- Mortgage valuation charges, if applicable.
- Conveyancing and legal disbursements.
- Survey costs, where you commission a survey.
- Stamp Duty Land Tax in England or Northern Ireland, Land and Buildings Transaction Tax in Scotland, or Land Transaction Tax in Wales, as applicable.
- Estate agent charges on the property being sold.
- Removals, insurance and other moving expenses.
- Mortgage broker fees, if charged.
These are not all costs caused by porting specifically. Many would also arise if you arranged a completely new mortgage. When comparing options, distinguish costs common to both routes from costs that change depending on the mortgage you choose.
MoneyHelper's buying and moving costs guide explains the main categories and why upfront mortgage charges should be considered alongside the wider cost of a property transaction.
Porting versus a new mortgage: a worked cost comparison
Suppose you are moving to a more expensive home and need to decide whether to preserve your existing mortgage rate or replace the whole loan.
Illustrative scenario only: These are invented comparison figures, not current lender quotations or representative market rates.
- Existing mortgage balance: £180,000.
- Existing fixed rate: 2.5%.
- Time remaining on the fixed deal: two years.
- Additional borrowing needed: £60,000.
- Rate on additional borrowing if porting: 5%.
- Alternative new mortgage: £240,000 at 4.5%.
- Potential ERC if the old mortgage is fully redeemed without qualifying porting relief: 3%, or £5,400.
Step 1: Compare the interest cost
For an initial screening calculation, assume each balance remains unchanged and calculate simple annual interest. This isolates the rate difference but does not calculate actual capital-and-interest mortgage repayments.
| Borrowing | Annual interest |
|---|---|
| Port £180,000 at 2.5% | £4,500 |
| Borrow £60,000 at 5% | £3,000 |
| Total with porting | £7,500 |
| New £240,000 loan at 4.5% | £10,800 |
Indicative annual interest difference: £10,800 − £7,500 = £3,300.
If balances and rates remained constant for two years, that would suggest a £6,600 interest advantage for the porting route before fees.
In a normal repayment mortgage, the outstanding balances decline as capital is repaid, so the actual difference would not be exactly £6,600. Monthly payments and remaining balances also depend on the repayment terms of each mortgage part.
Step 2: Include fees and early repayment charges
Now suppose the porting route has £500 of mortgage-specific fees, while replacing the entire mortgage involves £1,500 of mortgage-specific fees plus the £5,400 ERC.
These amounts are also illustrative. Assume that both routes incur the same property purchase costs and that the quoted fees are payable in cash rather than added to the mortgage.
| Two-year simplified cost | Port | Replace |
|---|---|---|
| Interest, constant-balance assumption | £15,000 | £21,600 |
| Mortgage-specific fees | £500 | £1,500 |
| Early repayment charge | £0 | £5,400 |
| Illustrative total | £15,500 | £28,500 |
Under these deliberately simplified assumptions, porting appears £13,000 cheaper over two years.
What this result means: Preserving an inexpensive existing rate can be financially significant, particularly when porting also avoids a substantial ERC.
What it does not mean: Porting will save £13,000 on an actual repayment mortgage. A proper comparison must calculate scheduled repayments, changing principal balances, fees, the date the old deal expires and the rates that apply afterwards.
Step 3: Stress-test the comparison
The conclusion changes if the lender charges a much higher rate for additional borrowing or if the current fixed deal has little time remaining.
For example, if the original deal expires after six months rather than two years, the advantage of the existing 2.5% rate lasts for much less time. A comparison that assumes it remains available for two full years would overstate the benefit.
Ask your broker to compare the same future dates under both options. Include the remaining mortgage balance at each comparison date, not just the sum of monthly payments.
Why can a lender refuse to port your mortgage?
One of the most consequential misunderstandings is assuming that a portable mortgage gives an unconditional right to take the same rate to any suitable-looking property.
In practice, several issues can prevent approval.
Income and affordability changes
Your financial circumstances may have changed since the existing mortgage was approved.
Examples include reduced earnings, becoming self-employed, higher childcare costs, new debts or a change in household income.
For many porting applications, the lender assesses whether the proposed new mortgage remains affordable. Additional borrowing can make this assessment more demanding.
There is an important regulatory nuance. The Financial Ombudsman Service's guidance on early repayment charge complaints explains that FCA rules can permit lenders to agree certain porting applications without a detailed affordability assessment when no additional borrowing is involved.
Therefore, a refusal solely on affordability grounds is not automatically fair or unfair. The relevant rules, whether borrowing is increasing, the lender's other legitimate criteria and the individual circumstances all matter.
Loan-to-value restrictions
Loan-to-value (LTV) compares the amount borrowed with the lender's valuation of the new property.
For example, a £180,000 mortgage against a property valued at £200,000 produces an LTV of 90%.
If the product you want to port is available only within a lower LTV limit, your proposed borrowing might not qualify. A larger deposit or partial repayment could change that calculation.
Property eligibility
The lender also needs to accept the property as security for its lending.
A property may require closer examination because of its construction, condition, lease terms or other characteristics. A home that looks affordable to the buyer is not automatically acceptable to the lender.
Consider checking property eligibility early if you are buying an unusual construction type, a very short-lease property, or a home requiring substantial renovation.
Changes to the borrowers or mortgage structure
Adding or removing a borrower, changing the repayment term, switching repayment type or otherwise restructuring the borrowing can introduce additional criteria.
The lender may assess the new arrangement differently from a straightforward application to carry forward an unchanged balance.
What happens if you move to a cheaper home?
Downsizing creates a different problem from moving to a more expensive property.
Suppose your outstanding mortgage is £220,000, but you only need £150,000 against the next home.
You may wish to port £150,000 and repay the other £70,000 from the sale proceeds.
The lender might permit this, but an ERC could apply to some of the balance being repaid, depending on the product rules and any permitted penalty-free repayment allowance.
For an illustrative calculation, a 2% ERC on the full £70,000 would be £1,400, assuming the lender applies the charge to that entire amount and no exemptions apply.
Do not assume that a successful partial port removes every possible early repayment charge. Ask for a written illustration showing exactly how the existing balance will be divided between ported and repaid borrowing.
What if your sale and purchase do not complete together?
Moving dates can create costs even when the underlying mortgage product is portable.
If you sell first and purchase later, the old loan may need to be redeemed before the new one starts. Your lender may provide a temporary porting window during which a qualifying new mortgage can lead to the repayment or refund of an ERC.
But the duration, permitted borrowing amount, application conditions and refund procedure vary by lender.
Ask these questions before you exchange contracts:
- Must the sale and purchase complete on the same day?
- What is the maximum gap the lender allows?
- Will an ERC be collected when the original mortgage is redeemed?
- If it is collected, what exact conditions apply to a refund?
- Does porting a lower balance reduce the refund?
- What happens if the new purchase fails or the porting application is refused?
Build your completion budget around the amount that actually needs to be paid at the relevant date, rather than assuming an ERC refund will arrive immediately.
Port, borrow more, or replace everything?
For many homeowners moving up the property ladder, the real choice is between preserving part of the existing mortgage and refinancing the full amount.
| Option | Main benefit | Main risk |
|---|---|---|
| Port existing balance only | Keeps eligible existing deal | Must meet new property and lender requirements |
| Port and borrow more | Protects existing rate on one part | Extra borrowing may carry higher rates and separate expiry dates |
| Replace the entire mortgage | May simplify borrowing into one deal | ERC and new borrowing costs may outweigh savings |
A split mortgage can produce two or more parts with different rates and product expiry dates. Each part may have separate ERC conditions, so the arrangement can require more attention when switching products later.
A single new deal may be simpler to manage, but simplicity alone is not a reason to pay thousands of pounds in additional interest or penalties.
A practical checklist before applying to port
Request the information below from your lender or mortgage broker before committing to the purchase.
- Current borrowing: Outstanding mortgage balance, rate, remaining deal period, mortgage term and ERC schedule.
- Porting rights: Exact terms governing eligibility, timing and any minimum or maximum amount that may be transferred.
- New property: Expected valuation, LTV limits and property eligibility requirements.
- Affordability: Evidence needed for income, expenditure and any additional borrowing.
- Additional borrowing: Available rates, fees, mortgage term and separate product expiry dates.
- Moving dates: What happens if the sale and purchase are not simultaneous.
- Alternative quote: A full new mortgage illustration showing all relevant charges.
- Cash requirement: Deposit, transaction costs, any initially payable ERC and an appropriate emergency reserve.
Then ask for two comparable mortgage illustrations using the same anticipated completion date and a clearly defined comparison period.
What should you do if porting is refused?
First, ask the lender or broker to identify the specific reason for refusal. Find out whether the problem concerns affordability, the property, LTV, additional borrowing, the proposed borrowers or another product condition.
A refusal may sometimes be resolved by changing the proposed borrowing amount or property. In other circumstances, another lender or a different purchase may be necessary.
If you believe the lender acted unfairly, particularly where a porting refusal left you facing an ERC, use the lender's formal complaints procedure and consider referring an unresolved eligible complaint to the Financial Ombudsman Service.
The Ombudsman has considered cases where a lender refused porting after changing its lending criteria. In one published case involving a borrower affected by a changed age limit, it concluded that the resulting ERC and additional costs should be addressed.
That outcome depended on the particular facts. It does not mean every refused porting application entitles the borrower to an ERC refund.
Frequently asked questions
Can I port a mortgage if I need to borrow more?
Potentially, yes. Your lender may permit you to port the existing eligible balance while taking out extra borrowing on a separate product. The additional amount is subject to the lender's criteria and may attract different rates and fees.
Does porting mean I keep exactly the same monthly payment?
Not necessarily. Even where your existing interest rate is preserved, the repayment term, ported balance and any additional borrowing can change the overall monthly amount payable. Ask for a complete payment illustration.
Can I port a mortgage to a less expensive property?
Possibly. But downsizing may mean you repay part of the existing balance, which could trigger an ERC on that portion. The lender's LTV and property requirements still apply.
Is a portable mortgage guaranteed to be approved?
No. The existence of a porting feature and approval of a future application are different things. However, where a lender refuses porting and charges an ERC, the circumstances of the refusal may be relevant to whether the charge was applied fairly.
Should I port if my fixed rate is almost finished?
Not automatically. A rate with only a short period remaining may deliver limited savings. Compare the fees and future products available after the original rate ends with the cost of taking a new mortgage now.
Bottom line: compare the full cost, not just the rate
Porting a mortgage can be financially attractive when it protects a favourable interest rate and prevents a costly early repayment charge. But it is not a shortcut around lender approval, nor does it eliminate the normal costs of buying and selling property.
The most useful next step is to request a written porting illustration and a competing new-mortgage illustration before relying on either option in your moving budget.
Compare the upfront cash required, monthly payments, total interest and fees over the same period, remaining balances, and what happens when each fixed-rate product ends. Confirm the porting deadline and ERC conditions in writing, and avoid assuming approval until the lender has assessed the actual proposed transaction.
This guide is for general educational purposes and focuses on UK residential mortgages. It is not personalised mortgage, legal or tax advice. Lender criteria, product terms and applicable property taxes depend on your circumstances and location.
