How can I determine if porting my mortgage is a viable option when selling during a fixed term?

Porting a mortgage during a fixed term is viable when your lender permits the existing product to move to a new property and the financial and practical conditions of the transfer work for you. The decision depends on more than the interest rate: assess the lender’s portability rules, the amount you need to borrow, the value and type of the new property, the timing of both transactions and the cost of ending the current mortgage instead.

Start by checking whether the mortgage is genuinely portable. Portability is a feature of some mortgage products, but it is not an unconditional right to transfer the loan. Read the mortgage offer and current terms, then ask the lender to confirm:

• whether the product can be ported before the fixed term ends;
• whether the transfer must happen at the same time as the sale and purchase;
• how long any mortgage offer or porting approval remains valid;
• whether the new property is acceptable security under its lending policy;
• whether a fresh application, valuation and legal work will be required; and
• what happens if the sale completes but the purchase is delayed or falls through.

These conditions matter because a portable mortgage is normally assessed as a new lending application. The lender can review your income, expenditure, debts, credit history and loan-to-value position again. A previous approval does not necessarily mean the transfer will be accepted, particularly if your circumstances or the lender’s criteria have changed.

Calculate how the new borrowing would be structured. Compare the balance that can be transferred with the amount required for the replacement property. There are usually three possible outcomes:

• You borrow a similar amount: the existing fixed-rate product may cover the replacement loan, subject to the lender’s approval and the new property’s valuation.
• You need to borrow more: the additional borrowing may be placed on a separate mortgage product, potentially with a different rate, fixed period and fees. Consider how the two parts would be affected if you later remortgage or repay them.
• You need to borrow less: the lender may allow only part of the existing loan to be transferred. Establish whether any remaining balance is treated as an early repayment and whether a charge applies to that portion.

Ask the lender for a written illustration showing the balance being ported, any extra borrowing, the monthly payments, the remaining fixed period and the costs payable at each stage. Do not rely solely on the advertised rate, because a lower purchase price, a different loan size or a new product for additional borrowing can change the overall cost.

Compare porting with redeeming the mortgage. Request a redemption statement for the proposed sale date and a separate projection for the porting route. The comparison should include the lender’s administration and product fees, valuation and legal costs, any cost of arranging additional borrowing, and the interest payable under each option. Check whether the current rate remains competitive compared with the products available if you repay and arrange a new mortgage.

Also check the fixed-rate end date. If the sale and purchase can be completed after the fixed period expires, waiting may change the calculation, although this must be balanced against the risk of moving onto the lender’s follow-on rate or incurring other costs. A lender or mortgage adviser can explain the exact dates and conditions that apply to your product.

Examine the timing and chain risk. Porting often depends on the sale of the existing home and the purchase of the next one progressing in a coordinated way. Your conveyancer should confirm how the mortgage will be redeemed on the sale and applied to the purchase. If there is a gap between transactions, ask whether temporary finance is required and whether the lender will hold the porting terms during that gap. Any bridging or short-term borrowing would need its own affordability and cost assessment.

The new property may also create issues that are unrelated to its price. The lender can reject or restrict lending because of its construction, lease terms, condition, location, title or valuation. A mortgage valuation is not a full survey, so consider obtaining an independent survey where appropriate. If the valuation is lower than the agreed purchase price, you may need a larger deposit or different borrowing structure.

Use a written decision checklist. Porting is more likely to be suitable where:

• the lender confirms that the product can be transferred on acceptable terms;
• the new property passes the lender’s valuation and security requirements;
• your current income and expenditure support the proposed borrowing;
• the required loan amount fits the porting rules without creating an unsuitable second mortgage;
• the sale and purchase timetable meets the lender’s conditions; and
• the total cost and payment structure compare favourably with redeeming and arranging a different mortgage.

It may be less suitable if you are moving to a significantly cheaper property, need substantially more borrowing, have an uncertain completion timetable or would be tied to an unattractive rate for longer than necessary. It can also be impractical if the lender will not accept the property or if your circumstances no longer satisfy its affordability assessment.

Before committing to a sale or purchase, obtain the lender’s porting decision, a redemption statement and a mortgage illustration based on the proposed figures. Ask a regulated mortgage adviser to compare the available routes, and instruct your conveyancer to check the mortgage conditions and completion requirements. The final decision should be based on the complete cost, the monthly payment, the flexibility of the resulting mortgage and the risk that the linked transactions may not complete as planned.