Mortgage Porting: How Transferring Your Mortgage Deal to a New Property Works

When people move home, one question that frequently arises is what happens to their existing mortgage. For many borrowers in the UK, there is a feature built into their mortgage product called portability — a mechanism that allows certain mortgage terms to follow them from one property to another. This article explains how mortgage porting works in the UK: what it is, what the rules are, what regulatory framework governs it, and where the most common misunderstandings tend to arise. It does not constitute financial or legal advice.

Mortgage porting is the process of transferring an existing mortgage product — its interest rate, terms, and conditions — from a current property to a new one when moving home. It is the deal or rate that is portable, not the loan itself. Porting is not automatic. Even if a mortgage is designated as portable, the borrower must make a new application to their existing lender and will need to meet that lender's current lending criteria. Approval is not guaranteed. Most UK mortgages are portable, but not all. Some specialist products and buy-to-let mortgages are less commonly portable. The starting point is always to confirm whether the specific mortgage product carries a portability feature — this information is found in the original mortgage offer documentation.

What "Porting" Actually Means

The term "porting" is sometimes misunderstood. People occasionally assume it means the loan account itself moves to a new property in an administrative sense. In practice, what transfers is the product — the interest rate and associated terms. The existing mortgage is effectively redeemed on the sale of the current property, and a new mortgage is taken out on the new property using the same product terms, assuming all conditions are met. Because a new mortgage is being created, the lender treats this as a new application. This means the borrower goes through underwriting again: income, expenditure, credit history, and property valuation are all assessed afresh. The FCA's Mortgages and Home Finance: Conduct of Business Sourcebook (MCOB) governs this process, specifically MCOB 11.6, which sets out responsible lending obligations including affordability assessments.

The Affordability Assessment

Under MCOB 11.6.2R, lenders are required to assess affordability before entering into or varying a regulated mortgage contract. This applies to porting applications. The borrower's financial circumstances at the time of the new application are what matter — not their circumstances when the original mortgage was taken out. There is, however, an exception set out in MCOB 11.6.3R(1). A full affordability assessment is not required where: (a) the new contract is a replacement for an existing contract with the same firm; and (b) no additional borrowing is involved beyond financing product or arrangement fees; and (c) there is no change to terms that would be material to affordability. Where these conditions are met, lenders may agree a porting application without conducting a detailed affordability assessment.

The Property Valuation

Porting approval depends not only on the borrower's financial position but also on the new property itself. Lenders conduct a valuation survey on the new property as part of the application process. Some property types — particularly non-standard construction — may not meet the lender's lending criteria, and the Financial Ombudsman Service has upheld lender decisions to decline porting on this basis.

Additional Borrowing

If the new property costs more than the existing outstanding mortgage balance, the borrower may need to borrow more. This additional amount is treated as new lending and is subject to current market rates rather than the existing ported rate. The result is a "split loan" or multi-part mortgage: one portion carries the ported product rate, and the additional amount carries a new rate, potentially with a different end date. At NatWest, additional borrowing below £10,000 is charged at the Standard Variable Rate (SVR) rather than a new fixed rate. Additional borrowing of £10,000 or more provides access to new business rates. These thresholds reflect individual lender policy and are subject to change.

Borrowing Less Than the Existing Balance

If the new property costs less than the current one and a smaller loan is needed, the borrower is porting only a portion of the existing balance. The remainder of the balance that is not ported is effectively an early repayment, and Early Repayment Charges (ERCs) may apply to that portion.

Confirming Portability

The first requirement is that the mortgage product must be designated as portable. This is confirmed through the original mortgage offer documentation. Not all products carry this feature, and it is the borrower's responsibility to check before assuming portability is available.

Porting Windows and ERC Refunds

In most cases, the sale of the existing property and the purchase of the new property happen simultaneously — both complete on the same day. In this scenario, no ERC is triggered when the full balance is ported. Where completion is not simultaneous — for example, where the sale of the existing property completes before the purchase of the new one — the borrower will redeem the mortgage on sale and pay any applicable ERC at that point. Most major lenders operate a porting window during which the ERC is refunded once the new purchase completes: Barclays operates a 90-day window. If the new mortgage completes within 90 days of the original redemption, the ERC is refunded. Nationwide operates a 180-day window, and reports that ERC refunds are processed within 5 working days of the new completion. The product term is treated as paused during the gap period. Halifax operates a window of approximately 3 to 6 months, though some variation in reported timeframes exists across sources. If a new purchase does not complete within the applicable window, the ERC is not refunded and the ported rate is lost.

Early Repayment Charges and Overpayment Allowances

Where a partial port is involved — that is, where the new loan is smaller than the existing balance — ERCs apply to the amount not being ported, less any available overpayment allowance. Most UK mortgages include an annual overpayment allowance, which in many cases is around 10% of the outstanding balance per year, though some lenders offer higher allowances. NatWest, Metro Bank, and Atom Bank are among those reported to offer allowances of around 20%, though individual product terms will always take precedence. ERCs on fixed-rate mortgages during the fixed period are typically a percentage of the loan balance, and in many cases that percentage reduces over the fixed rate term — for example, starting at around 5% in the first year and stepping down in subsequent years. However, the precise structure depends on the specific product.

Loan-to-Value Considerations

In most cases, lenders require that the ported loan does not increase the loan-to-value (LTV) ratio relative to the current mortgage. If a borrower moves to a lower-value property while maintaining the same outstanding loan amount, the resulting LTV will be higher, which may not meet the lender's criteria. How strictly this is applied varies between lenders.

The Modified Affordability Assessment

Separately from porting, the FCA's MCOB 11.9 framework includes a Modified Affordability Assessment (MAA) designed for eligible customers remortgaging with no additional borrowing. To qualify for this streamlined assessment, a borrower must have a current mortgage, be up to date with payments for the preceding 12 months, not be seeking additional borrowing (beyond fees), and be switching to a new deal on the current property. As of July 2025, following FCA Policy Statement PS25/11, the MAA was extended to cover new lender mortgages that are more affordable than either the current mortgage or the available new deal from the existing lender. The MAA applies to product transfers on the current property rather than to porting to a new one, but it forms part of the same regulatory framework governing responsible mortgage lending.

The Consumer Duty

The FCA's Consumer Duty (PRIN 2A) applies to regulated mortgage contracts. It requires firms to act to avoid foreseeable harm and to support customers in making informed decisions. This does not affect the mechanics of porting directly but forms part of the broader conduct framework within which lenders operate. The Consumer Duty does not apply to unregulated buy-to-let contracts.

"My Mortgage is Portable, So Porting Is Guaranteed"

Portability means the feature exists — it does not guarantee approval. The borrower must still pass a new underwriting assessment, and the new property must meet the lender's criteria. A change in financial circumstances since the original mortgage was taken out — such as a reduction in income, a change in employment status, or an adverse credit event like a default — will be reflected in the new assessment.

"Porting Means No Early Repayment Charges"

This is not always the case. If the sale and purchase complete simultaneously and the full balance is ported, ERCs are typically not triggered. However, if completion is not simultaneous, an ERC may be paid upfront and refunded only if the new purchase completes within the lender's porting window. And if less than the full balance is ported, ERCs apply to the unported portion, subject to any available overpayment allowance.

"Additional Borrowing Gets the Same Rate"

Additional borrowing beyond the existing balance is treated as new lending and carries current market rates. This creates a split loan structure with different rates, different end dates, and potentially different product terms. The two parts of the mortgage need to be managed accordingly.

"Porting is Always Cheaper Than Remortgaging"

Whether porting is less costly than switching to a new lender depends on a range of variables: the existing rate compared to available market rates, the size of any applicable ERC, the arrangement fees on the ported product and any additional borrowing, and the rates applied to additional lending. No universal rule applies. These factors vary by borrower and by prevailing market conditions.

Interest-Only Mortgages

Interest-only mortgages can in many cases be ported, though this is not universal across lenders. The Financial Ombudsman Service has noted that it may be unfair to refuse porting solely on the grounds that a mortgage is interest-only. However, if additional borrowing is required alongside the ported portion, lenders may require that the additional element is on a capital repayment basis. This may vary depending on lender policy and the specific product.

Changing Names on the Mortgage

In some circumstances, borrowers can port a mortgage while also changing the names on the application — for example, following a divorce where they are moving from a joint mortgage to a sole mortgage, or vice versa. Nationwide's intermediary documentation confirms this is possible for their products, subject to affordability assessment and lending criteria. Whether other lenders permit this depends on individual policy.

NatWest "Track and Switch"

NatWest offers a product feature described as "Track and Switch" porting, which allows a customer to switch to a new fixed rate without triggering an ERC while porting. Under this arrangement, the case is not keyed as a conventional porting application. This is a product-specific feature and not a general industry arrangement.

Affordability Stress Testing and Remaining Fixed Rate Term

In some cases, the affordability calculations applied to a porting application may differ depending on how long remains on the fixed rate term being ported. An FOS decision (reference DRN-3549093) involving Santander illustrated that where the ported mortgage had fewer than five years remaining on the fixed rate, different affordability criteria were applied compared to a new five-year or longer fixed rate mortgage. This may vary depending on the lender and the specific terms.

Buy-to-Let Mortgages

Buy-to-let mortgages are less commonly portable than residential mortgages. Borrowers with buy-to-let products should check their mortgage offer to confirm whether portability is available.

Non-Standard Construction Properties

Lenders have specific property criteria, and porting applications may be declined where the new property does not meet those criteria. Non-standard construction — for example, concrete or timber-framed properties — is one known area where declinations can occur. The FOS has upheld such decisions.

The Application Process

Even where a mortgage is portable and the borrower's circumstances are unchanged, porting involves a full application process with the existing lender. This includes obtaining a Decision in Principle (also known as an Agreement in Principle), which at this stage typically involves a soft credit search. A full application follows, involving a hard credit check, income and expenditure assessment, and a property valuation. The underwriting stage for a porting application typically takes in the range of two to six weeks, which is broadly comparable to a new mortgage application, though this can vary depending on lender workload and case complexity. Some lenders charge for the property valuation that forms part of this process. Others do not. Halifax, for example, is reported to charge approximately £100 for a valuation; NatWest offers free valuations for porting applications. These figures reflect lender policies at the time of publication and may change.

Simultaneous and Non-Simultaneous Completions

The simplest porting scenario is where sale and purchase complete on the same day. In this case, the ported balance transfers directly without any ERC exposure, provided the full balance is being ported. Where the sale completes before the purchase, the porting window becomes critical. The borrower pays off the existing mortgage on sale and, if applicable, pays an ERC. Provided the new purchase completes within the lender's porting window, that ERC is refunded. The product rate and terms are effectively preserved during the gap. Where the purchase falls outside the porting window, the rate is lost and the borrower would need to seek a new product, either with the same lender or elsewhere. This distinction matters in situations where a purchase falls through or is significantly delayed after a sale has completed.

NatWest Product Transfer Windows

NatWest allows customers to apply for a product transfer — a switch of rate on the existing property — up to four months before the current deal ends. This is a separate mechanism from porting, but it is relevant where a customer is considering their options in the period leading up to a move.

• Mortgage porting is the transfer of an existing mortgage product — its rate and terms — from one property to another. The loan itself is not transferred; a new application is made to the same lender using the existing product terms.
• Portability must be confirmed in the original mortgage offer. Most UK residential mortgages include the feature, but not all do, and buy-to-let mortgages are less commonly portable.
• Porting requires a full new application and underwriting process, including a credit check and property valuation. Changes in financial circumstances since the original mortgage was taken out will be assessed afresh.
• Under MCOB 11.6.3R, a full affordability assessment may not be required where porting involves no additional borrowing and no material change to terms — but this is an exception that lenders apply case by case.
• Where additional borrowing is needed, it is treated as new lending at current market rates. This creates a split loan structure with different rates and end dates.
• Where less than the full balance is ported, Early Repayment Charges apply to the unported portion, less any available overpayment allowance.
• Where sale and purchase do not complete simultaneously, lenders operate porting windows during which ERCs paid on redemption are refunded once the new purchase completes. Barclays operates a 90-day window; Nationwide a 180-day window; Halifax approximately 3 to 6 months. Purchases completing after the window closes result in the ERC being lost and the product rate falling away.
• The Financial Ombudsman Service has upheld lender decisions to decline porting applications on the basis of affordability assessment outcomes or property lending criteria, and has addressed questions around interest-only mortgages and non-standard construction properties.