Can You Port a Buy-to-Let Mortgage to Another Rental?

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You may be able to port a buy-to-let mortgage when replacing one rental with another, but portability is a feature to check, not an automatic right to move the debt anywhere you choose. The lender must accept the proposed transaction, property and borrowing.

Porting can preserve an attractive existing rate, while extra borrowing may need a separate product at a different rate. If you borrow less, an early repayment charge may apply to the amount repaid. Compare the whole transaction before deciding that keeping the old rate must be the cheapest route.

What does porting a mortgage mean?

Porting normally involves redeeming the old mortgage and taking a new mortgage with the same lender, carrying eligible product terms across to the replacement security. The mortgage charge is not simply picked up from one address and attached to another without assessment.

The property being purchased or offered as security still needs to qualify. Its rent, value, condition, tenure and use can all matter. The lender also needs to accept the borrower’s current circumstances and any proposed ownership changes.

Read your existing offer to establish whether the product is portable. Then ask the lender or broker how the actual transaction would be handled. A generic statement that a lender “does porting” does not establish the terms for your account.

Published policies can differ materially

Checked on 19 October 2026, The Mortgage Works’ porting guidance permits eligible moves to another property in a client’s portfolio or a new lettable buy-to-let property. It requires a full mortgage application and simultaneous completion of the old and new mortgage.

Its guidance also distinguishes a full-balance port, a partial redemption and extra borrowing. The additional amount does not automatically receive the existing rate. Product incentives such as free legal work, cashback and free valuation are not portable under that published policy.

Other lenders can set different conditions. For example, Santander’s published buy-to-let criteria distinguish a house purchase from porting to a property being remortgaged or owned mortgage-free. Check the relevant current policy rather than applying another lender’s flexibility to your loan.

A two-part loan example

Suppose you can port a £100,000 interest-only balance at 3.5% and need £40,000 of additional borrowing at an illustrative 5.5%. Assume both rates apply for the full comparison year and the proposed lender approves the combination.

The monthly interest is £475. Borrowing the full £140,000 at 5.5% would cost £7,700 annually, or £641.67 monthly. The illustrative ported combination saves £2,000 in annual interest, before comparing fees and the remaining period on the old rate.

Use the mortgage stress calculator for each loan part. Do not enter the whole new balance at the old rate: that would understate the cost whenever additional borrowing has different terms.

The old rate’s expiry matters

If the 3.5% product ends in six months, the first-year saving is not the same as a full year at that rate. Record the deal-end date for each part and the assumed payment after it ends. A blended rate is a snapshot, not necessarily the rate for the next two or five years.

Two parts can also have different early repayment terms and expiry dates. That may complicate a later remortgage because one part becomes available to switch while the other remains within a charge period.

The deal-expiry planning guide helps map those dates. Keep the ported amount and additional borrowing as separate lines so the future refinancing requirement remains visible.

What if the replacement mortgage is smaller?

Suppose your existing balance is £120,000 but you only need £90,000 on the replacement property. The £30,000 difference is repaid. If the contract applies a 3% early repayment charge to that repaid amount, the illustrative charge is £900.

That is different from a £3,600 charge on the full £120,000 balance. But the actual charge, allowances and permitted port depend on the existing terms and lender policy. Obtain a specific redemption and porting calculation rather than using a percentage from memory.

Read the early repayment charge guide to compare paying a charge with the cost of retaining the product. Porting should serve the replacement investment, not become a reason to buy an unsuitable property solely to avoid an exit fee.

Check the replacement property’s borrowing capacity

A new property may have a different rent-to-price relationship from the one being sold. An old £100,000 mortgage does not prove the lender will accept the same balance on a lower-rent replacement, even if the purchase price is similar.

Ask for the current affordability calculation and the value used for LTV. Where additional borrowing is needed, check how the lender assesses both parts together, what stress rate it uses and whether fees added to the loan reduce the amount available for the purchase.

Confirm property restrictions early. A flat above commercial premises, unusual title or major refurbishment can change the lender shortlist. A portable product does not remove those restrictions or turn an unlettable property into acceptable buy-to-let security.

Get the completion sequence clear

The sale, redemption, purchase and new advance need a coherent legal timetable. Where simultaneous completion is required, a broken chain can affect the port. If you intend to sell first and buy later, ask specifically whether any gap is permitted and how charges or refunds would work.

Do not assume an early repayment charge paid on sale will automatically be refunded when you eventually buy something else. Obtain the lender’s conditions, permitted timescale and application requirements in writing if such an arrangement is offered.

The solicitor should have the lender’s instructions and accurate redemption figures. The broker should know the likely completion sequence. Avoid giving each adviser a different version of whether you are selling, retaining or refinancing the original property.

Include costs beyond the interest saving

Porting does not remove the usual costs of selling one investment and buying another. Budget for legal work, valuation, taxes where applicable, estate-agency charges, initial work and empty periods. Check which mortgage incentives, if any, apply to the new transaction.

Compare these against the benefits of the replacement property. A £2,000 annual interest saving does not justify £15,000 of extra transaction costs by itself, particularly if the old rate expires soon. The new property needs its own investment case.

Use the deal calculator to assess the replacement with the actual split mortgage and costs. Also review the cost-to-sell guide so that the cash released from the old property is not overstated.

Run a second calculation where the property sale achieves less than expected. If the net sale proceeds fall by £10,000, establish whether the replacement purchase needs extra cash or borrowing. The ported balance itself does not increase merely because the deposit available from the sale is smaller. Confirm the revised funding still fits before accepting a lower sale offer.

Check ownership and purpose changes

Tell the lender if the new property will have different owners or a company borrower. A product attached to your personal borrowing cannot be assumed to move into an SPV. Adding or removing a borrower also needs the lender’s agreed process and legal work.

If the replacement will become your own home or house a family member, disclose that at the beginning. A buy-to-let product is not portable to any intended use. The replacement loan needs to match the actual occupation and mortgage classification.

Ask for a written comparison between the proposed port and a new mortgage. List the available borrowing, fees, early repayment costs, dates and future deal expiries. That gives you a useful decision even if the existing rate initially appears too attractive to give up.

Questions about buy-to-let porting