Porting Your Mortgage to a New Build Home

Published by New-Builds Team · 2025

Moving to a new build home is an exciting prospect, but if you are currently locked into a fixed-rate mortgage with time still remaining, the prospect of paying thousands of pounds in early repayment charges (ERCs) can take the shine off the experience. This is where mortgage porting comes into play — the process of transferring your existing mortgage deal from your current property to your new one, preserving your current interest rate and avoiding the ERCs that would otherwise apply if you repaid the mortgage early. For homeowners who secured favourable fixed rates during periods of lower interest rates, porting can represent a significant financial saving, particularly in the current environment where new mortgage products may be considerably more expensive than the deal you already have. The concept sounds straightforward, but the practical reality of porting a mortgage to a new build property involves a number of complexities that buyers need to understand before assuming it will work smoothly.

Mortgage porting is not a right that borrowers can exercise unilaterally — it requires the lender's approval, and that approval is subject to the same underwriting criteria as a new mortgage application. The lender will reassess your affordability, conduct a new valuation of the property you are moving to, and apply their current lending criteria to the transaction. For new build purchases, additional complexities arise from the lender's specific policies on new build lending, the timing challenges inherent in construction programmes, and the potential need for additional borrowing if the new property costs more than the existing one. Understanding how porting works, whether your lender allows it for new build purchases, what the process involves, and how to weigh porting against the alternative of remortgaging to a completely new deal is essential knowledge for any homeowner contemplating a move to a new build. In this comprehensive guide, we will cover every aspect of porting your mortgage to a new build home, with practical guidance on navigating the process effectively and making the right financial decision for your circumstances.

What Does Porting a Mortgage Mean?

Mortgage porting is the process of transferring your existing mortgage product — including the interest rate, remaining fixed-rate period, and associated terms — from one property to another. In effect, you repay the mortgage on your current property from the proceeds of its sale and simultaneously take out a new mortgage on the new property, but with the same rate and terms as your existing deal. The mortgage charge (the legal claim on the property that secures the loan) is released from the old property and applied to the new one, but the underlying product remains the same.

The primary benefit of porting is the avoidance of early repayment charges. Most fixed-rate mortgages include ERCs that apply if you repay the mortgage during the fixed-rate period, typically charged as a percentage of the outstanding loan balance. These charges can be substantial — often 3% to 5% in the early years of a five-year fix, declining to 1% in the final year. On a £200,000 mortgage balance, a 3% ERC would amount to £6,000 — a significant sum that most borrowers would prefer to avoid. By porting the mortgage rather than repaying it, you side-step this charge entirely.

The second key benefit of porting is rate preservation. If you secured your current mortgage at a time when interest rates were lower than they are today — as many borrowers did during the period from 2020 to early 2022 when rates were at historic lows — porting allows you to keep that favourable rate for the remainder of your fixed period. For example, a borrower who fixed at 2.5% in early 2022 and is now looking to move in 2025 would face current fixed rates of approximately 4.0% to 5.0% if they remortgaged. By porting, they can retain their 2.5% rate for the remaining term of the fix, potentially saving thousands in interest payments.

However, porting is not always straightforward, and it is important to understand that a "port" is technically a new mortgage application assessed against the lender's current criteria. It is not simply an administrative transfer of the loan from one property to another. The lender will re-evaluate your affordability, reassess the loan-to-value ratio based on the new property's value, and apply any lending policy changes that have occurred since your original application. If your circumstances have changed — for example, if your income has reduced, you have taken on additional debt, or you have changed employment status — the port may not be approved even though you are currently servicing the existing mortgage without difficulty.

Can You Port to a New Build Property?

The ability to port your mortgage to a new build property depends on your lender's policies, and this is where many borrowers encounter unexpected obstacles. While most major UK lenders allow porting in principle, not all of them permit porting onto new build properties, and those that do may impose additional conditions or restrictions that affect the viability of the process.

The major high-street lenders generally allow porting to new build properties, though with varying conditions. Nationwide permits porting to new builds and has a well-established process for handling the timing complexities involved. Halifax (Lloyds Banking Group) allows porting to new builds and has one of the most experienced new build lending teams in the UK. Barclays permits porting but may require a new valuation of the new build property, and their policies on off-plan purchases should be confirmed at the time of application. NatWest allows porting to new builds with standard new build lending criteria applying. HSBC permits porting but has specific timescale requirements for new build transactions that need to be carefully managed.

The restrictions that some lenders impose on new build porting typically relate to: the maximum LTV on the new property (which may be lower for new builds than for existing properties — potentially capped at 85% or 90% rather than 95%); the type of new build property (some lenders restrict porting onto certain property types such as studio apartments, properties above commercial premises, or high-rise apartments); the completion timescale (some lenders require the new build to be at a certain stage of construction before they will process the port); and the development itself (some lenders maintain approved developer lists and may not port onto properties built by developers not on their panel). These restrictions can create a mismatch between what the borrower needs and what the lender will allow, necessitating careful planning and potentially compromising on the choice of property or lender.

The Porting Process: Step by Step

Porting your mortgage to a new build involves a structured process that runs in parallel with the sale of your existing property and the purchase of the new one. Understanding each step and the associated timescales is essential for keeping all the moving parts aligned.

Step 1: Confirm portability with your lender. Before making any commitments on a new build purchase, contact your lender (or ask your broker to do so) to confirm that your current mortgage product is portable and that the lender permits porting onto new build properties. Request specific details on any new build restrictions, maximum LTV for the port, and any additional requirements or documentation that will be needed. This initial enquiry should also confirm how long you have to complete the port — most lenders require the port to be completed within a specified period (typically 30 to 90 days) of the sale of the existing property completing. This is a critical timescale for new build purchases, where there may be a gap between selling your current home and the new build being ready for occupation.

Step 2: Assess your borrowing needs. If the new build property costs more than your existing mortgage balance (which is common, as people typically move to more expensive properties), you will need additional borrowing on top of the ported amount. This additional borrowing is arranged as a separate mortgage product alongside the port, typically at the lender's current rates rather than the ported rate. You will therefore end up with two mortgage components running in parallel on the same property: the ported element at your existing rate and the additional borrowing at the current rate. Some lenders also allow you to port less than your existing balance if the new property is cheaper — in this case, you may need to repay the excess, and ERCs may apply to the portion being repaid rather than ported.

Step 3: Submit the porting application. The porting application is effectively a new mortgage application assessed against the lender's current criteria. You will need to provide full documentation including proof of income, bank statements, proof of identity and address, and details of the property you are purchasing. The lender will conduct a new affordability assessment based on your current income and expenditure, run a credit check, and arrange a valuation of the new build property. If additional borrowing is required, this will be assessed alongside the port application, with the combined monthly payments stress-tested against the lender's affordability model.

Step 4: Coordinate the timing. This is where porting to a new build becomes particularly challenging. In an ideal scenario, the sale of your existing property and the purchase of the new build complete on the same day, allowing the ported mortgage to transfer seamlessly from one property to the other. In practice, this rarely happens with new build purchases because the completion date for the new build is often uncertain and may not align with your buyer's timeline on the property you are selling. Most lenders allow a "port gap" — a period between the sale of the old property and the completion of the new purchase during which the mortgage is effectively in limbo. The maximum port gap varies between lenders, typically ranging from 30 to 90 days. If the gap exceeds the permitted period, the port may lapse and ERCs could become payable.

Step 5: Complete on the new property. Once the new build is ready and all legal requirements are satisfied, the purchase completes and the ported mortgage is applied to the new property. If you have additional borrowing, this is drawn down simultaneously. Your solicitor will handle the legal mechanics of releasing the mortgage charge on the old property and registering it against the new one. From this point, you continue making payments on the ported element at your original rate and on the additional borrowing at the new rate, until the respective fixed periods end.

Additional Borrowing: How It Works Alongside a Port

The vast majority of porting transactions involve additional borrowing, because most movers are upgrading to a more expensive property. Understanding how the additional borrowing component works alongside the ported element is important for calculating the true cost of the move and comparing it against the alternative of remortgaging entirely.

In a typical porting scenario, consider a homeowner with an existing mortgage of £180,000 at 2.49% fixed for five years (with three years remaining) who is purchasing a new build at £425,000. After selling their current property and applying the equity plus savings, they need total borrowing of £300,000. The ported element is £180,000 at 2.49% (continuing the original fix), and the additional borrowing of £120,000 is arranged at the lender's current rate of, say, 4.49% fixed for five years. The combined monthly payment is approximately £1,474 (£808 for the ported element and £666 for the additional borrowing). The blended effective rate across the combined borrowing is approximately 3.29% — significantly lower than the 4.49% they would pay on the entire £300,000 if they remortgaged without porting.

This blended rate advantage is the core financial case for porting. The larger the ported element relative to the additional borrowing, and the larger the rate differential between the ported rate and current market rates, the greater the benefit. However, the analysis is complicated by the fact that the ported element and the additional borrowing will typically have different end dates for their fixed periods. When the ported element's fix expires in three years, it will revert to the lender's standard variable rate (SVR) unless re-fixed — at which point the borrower will want to review the entire mortgage arrangement and potentially consolidate everything onto a single new deal.

Porting vs Remortgaging: Which Is Better?

The decision between porting and remortgaging is fundamentally a financial comparison, though practical and timing considerations also play a role. The correct choice depends on several variables: the rate on your existing mortgage, the rate available on a new mortgage, the ERC that would apply if you remortgage, the arrangement fee on a new product, and the remaining term of your existing fix.

Let us work through the comparison in detail. In the scenario above — porting £180,000 at 2.49% with £120,000 additional at 4.49% versus remortgaging the full £300,000 at 4.49% — the three-year cost comparison is illuminating. The porting option costs approximately £53,064 in total interest and payments over three years (£808 x 36 + £666 x 36 for interest components). The remortgage option costs approximately £57,348 in interest plus the £5,400 ERC, totalling £62,748. Porting saves approximately £9,684 over three years — a substantial sum that clearly favours the porting approach in this scenario.

However, there are scenarios where remortgaging is the better choice even when ERCs apply. If your existing rate is only marginally below current market rates (for example, if you fixed at 4.2% and current rates are 4.4%), the interest saving from porting is small and may be outweighed by the benefits of a completely fresh deal — such as a longer fixed period, better flexibility features, or the ability to borrow from a lender with more favourable new build criteria. Additionally, if you are in the final year of your fix where ERCs are typically at their lowest (often 1%), the cost of breaking the fix may be modest enough that remortgaging to a genuinely better product represents better value.

Your broker should run both calculations in full, factoring in all costs (ERC, arrangement fees, valuation fees, legal fees) and present a clear comparison. The calculation should consider not just the immediate cost but the total cost over the remaining term of the ported fix and beyond. In some cases, a hybrid approach may be optimal — for example, porting now and then remortgaging the entire balance onto a single new deal when the ported fix expires, taking advantage of the ported rate in the interim while positioning yourself for a clean consolidation at the first penalty-free opportunity. For new build buyers who qualify, combining a port with green mortgage incentives on the additional borrowing can provide even greater savings.

The Timing Challenge: Managing the Port Gap

The port gap — the period between selling your existing property and completing on the new build — is perhaps the most challenging practical aspect of porting to a new build. Unlike a standard chain transaction where the sale and purchase can be coordinated to complete on the same day, new build completions are driven by the construction programme and may not align with the timeline of your property sale.

Most lenders allow a port gap of between 30 and 90 days. This means you can sell your existing property, repay the mortgage, and then re-draw it on the new property within the permitted gap period without losing your ported rate or incurring ERCs. The specific port gap policies for major lenders include: Halifax — typically allows 90 days; Nationwide — typically allows 60 days; Barclays — typically allows 30 days (which can be challenging for new builds); NatWest — typically allows 60 to 90 days; HSBC — typically allows 90 days. These timescales can change, so always confirm the current policy with your lender before committing to a course of action.

If the port gap is likely to exceed your lender's permitted period — which is a real risk with new build purchases where completion dates can slip — you have several options. First, you can delay the sale of your existing property to bring the two completion dates closer together. This may mean remaining in your current home longer and potentially paying bridging costs or a higher mortgage rate during the overlap period. Second, you can ask the lender whether an extended gap is possible given the specific circumstances — some lenders will exercise discretion, particularly for new build transactions where the delay is caused by the construction programme rather than buyer-related issues. Third, you can explore temporary accommodation and renting while waiting for the new build to complete, which maintains the port gap timeline but introduces additional living costs that need to be factored into the financial analysis.

A fourth option that some experienced movers use is to arrange a bridging loan to cover the gap period. The bridging loan covers the purchase of the new build property while awaiting the sale of the existing one, and is repaid from the sale proceeds. Bridging finance is expensive (typically 0.5% to 1.5% per month) and carries its own risks, so it should only be considered when the financial benefit of porting justifies the bridging costs and when the sale of the existing property is assured. Your broker can model the full cost of a bridging solution and compare it against the alternative of paying the ERC and remortgaging without a port.

What If the Port Is Declined?

A port application can be declined for the same reasons as any mortgage application: the borrower fails the affordability assessment, the property fails the valuation, or the application falls outside the lender's current criteria. If your port is declined, you are not left without options, but you do need to act quickly and strategically.

If the decline is due to affordability, explore whether a longer mortgage term (reducing monthly payments) or a smaller additional borrowing amount (perhaps by increasing your deposit from savings or accepting a lower property price) would bring the application within affordability limits. Your broker can recalculate the numbers and, if appropriate, resubmit the application with the adjusted parameters. If the decline is due to the property — for example, if the lender will not lend on the specific new build development or property type — you may need to consider whether an alternative property that meets the lender's criteria would serve your needs, or whether the financial analysis supports remortgaging with a different lender that accepts the property.

If the port is declined and you proceed with your move by remortgaging, the ERC on your existing mortgage becomes payable. In this scenario, it is worth exploring whether your current lender will waive or reduce the ERC in recognition that you attempted to port and the decline was due to their decision rather than yours. While lenders are not obligated to waive ERCs in these circumstances, some will exercise discretion, particularly if the decline was marginal or based on a technicality rather than a fundamental affordability concern. Your broker can negotiate on your behalf, presenting the case for a reduced ERC as a customer retention measure. If you are faced with a down-valuation as part of the porting process, our guide on how mortgage valuations work for new builds provides detailed advice on next steps.

Porting and the Mortgage Offer Validity Challenge

As with any new build mortgage, the validity period of the mortgage offer is a significant consideration for porting transactions. The offer issued for the port (and any additional borrowing) will have a standard validity period, and if the new build is not ready for completion within that period, the offer may expire — creating the same issues discussed in our dedicated article on mortgage offer expiry for new builds.

The interaction between the port gap and the offer validity creates a particularly tight window for new build porting transactions. You need the new build to be ready within both the offer validity period and the permitted port gap from the sale of your existing property. If either of these timescales is breached, the porting arrangement may collapse — potentially leaving you facing ERCs on a forced remortgage. Managing these concurrent timescales requires careful planning, regular communication with the developer and lender, and the flexibility to adjust your strategy if timelines shift.

Practical Tips for a Successful New Build Port

Based on the complexities we have discussed, here are the key practical recommendations for anyone considering porting their mortgage to a new build property:

Start the process early. As soon as you begin considering a new build purchase, contact your lender or broker to discuss the porting option. Understanding your lender's new build policies, port gap allowances, and application timescales well in advance gives you the maximum flexibility to plan and coordinate the transaction effectively. Do not wait until you have reserved a property to begin these conversations — by that point, you may discover constraints that limit your options.

Work with an experienced broker. Porting to a new build is one of the more complex mortgage transactions, involving the interaction of multiple timescales, policies, and financial calculations. A broker who specialises in new build mortgages and has experience with porting can navigate these complexities far more efficiently than a generalist. They will know which lenders have the most port-friendly policies, how to structure the additional borrowing to complement the ported element, and how to manage the timing to minimise the risk of the port gap being breached.

Keep your finances stable. Because the port requires a fresh affordability assessment, any changes to your financial circumstances between your original mortgage and the porting application could jeopardise approval. Avoid taking on new credit commitments (car finance, personal loans, credit card spending), changing jobs, or reducing your working hours during the porting period. If changes are unavoidable, discuss them with your broker in advance so they can assess the impact and adjust the strategy accordingly.

Have a Plan B. Despite best efforts, porting does not always work out — the lender may decline the application, the timescales may not align, or the financial analysis may ultimately favour remortgaging. Having a contingency plan in place from the start ensures you can adapt quickly without jeopardising your new build purchase. Your Plan B should include alternative lender options for a full remortgage, a realistic assessment of the ERC cost, and clarity on how you would fund any additional costs.

Consider the long-term view. When making the porting vs remortgaging decision, think beyond the immediate fixed-rate period. What will your mortgage look like when the ported fix expires? Will you be in a position to consolidate and remortgage at that point? How does the split-rate structure of a ported mortgage with additional borrowing affect your financial planning and flexibility? A decision that saves money over the next three years but creates complications or inflexibility in year four may not be the optimal long-term choice. Your broker should help you model the full-term financial picture, not just the immediate savings.