What is mortgage porting and how does it work?

Mortgage porting explained (for home movers)

Mortgage porting is when you move home and keep your existing mortgage deal by transferring it to your new property. Instead of ending your current mortgage and taking out a completely new one for the whole balance, you “port” (carry over) the interest rate and product terms—subject to the lender’s approval.

Porting can be attractive if you are part way through a fixed rate or tracker and you want to avoid the disruption (and potential charges) that can come with switching deals early. However, it is not automatic. Even if your mortgage is described as portable, the lender will still reassess the arrangement for the new property and your updated circumstances.

What does “porting” actually mean?

It helps to understand that porting is not a literal transfer of your mortgage from one property to another in the way you might move a utility account.

In practice, when you sell your current home, your existing mortgage is repaid. The lender then sets up a new mortgage on the new property using the same deal terms you had before—if they agree to port them.

So, you are porting the product/terms, not the property.

How does mortgage porting work in practice?

Porting usually follows a process that looks similar to applying for a mortgage, with one key difference: the lender is considering whether they can transfer your existing product rather than offering a brand-new one.

While the exact steps vary by lender and product, the typical approach includes:

• Affordability and income review: your current income, outgoings and overall financial position are assessed again.
• Credit check: your credit profile is reviewed at the time of the move.
• Property assessment: the new property is valued and checked against the lender’s lending requirements.
• Confirmation of portability: the lender confirms whether the original mortgage terms can be transferred to the new purchase.

Because the lender is still lending on a new property, approval is based on whether they can lend on that property and whether you meet their criteria at the point you are moving.

Is every mortgage portable?

No. Porting depends on the terms of your original mortgage offer.

Some mortgages are designed to be portable, while others—particularly certain older deals or specialist products—may not allow it. Even where portability is included, the lender can still decline the porting request if the new situation does not meet their requirements.

What happens to your mortgage balance when you move?

How porting works depends heavily on whether you are borrowing more, borrowing less, or moving to a different loan-to-value position.

If you need to borrow more

If the new home costs more and you require additional borrowing, the ported portion typically covers the amount that matches your existing mortgage balance (subject to lender rules). Any extra borrowing is usually arranged separately.

This can mean you end up with more than one mortgage “part” after completion—often with different interest rates, deal types, or end dates.

If you need to borrow less (downsizing)

If you are moving to a cheaper property and your mortgage balance needs to reduce, porting may not transfer the full amount in the same way.

Depending on the lender and the terms of your current mortgage, you may face:

• Repayment of the excess (the part that can’t be carried over), and
• Potential early repayment charges on any portion that is repaid early (where applicable).

The key point is that downsizing does not automatically remove early repayment considerations.

Costs to consider when porting

Porting may help you avoid certain moving-related costs, but it does not necessarily mean “no fees”. Common items to budget for include:

• Valuation and/or assessment fees for the new property
• Legal costs for the transfer and completion process
• Any early repayment charges if part of the balance is repaid rather than ported
• Potential product/administration charges related to the new arrangement (especially if you need additional borrowing)

The overall cost picture depends on what portion is ported, what portion is repaid, and how the lender structures any extra borrowing.

Porting vs taking a new mortgage

Porting can be a sensible option, but it is not always the most cost-effective route.

Porting may be worth considering when:

• Your current deal is still competitive compared with what’s available for new borrowing
• You are part way through a fixed term and ending it early would be expensive
• You want continuity by keeping the same mortgage product with the same lender

A new mortgage may be worth exploring when:

• Market rates for new lending are lower than your current deal
• Your circumstances have changed in a way that could improve your options
• Your move would require significant additional borrowing, potentially priced less favourably than a new overall deal

In many real-world scenarios, the “best” choice comes down to how your mortgage will be structured after the move—particularly if you end up with multiple parts.

Key limitations and practical considerations

Mortgage porting is subject to lender approval, and there are a few practical realities to keep in mind:

• Porting isn’t guaranteed even if your mortgage is portable.
• Affordability and credit are reassessed at the time of the move.
• Loan-to-value can change, which may affect what can be ported.
• Timing matters: valuations, checks and approvals can take time, and delays can affect your property chain.

Summary: is mortgage porting right for your move?

Mortgage porting can be a useful way to carry your existing mortgage deal to a new property, potentially reducing disruption and helping you avoid certain early repayment charges—especially if your current rate is attractive.

However, it still involves a lender assessment, and the outcome depends on the new property, your updated circumstances, and how much you need to borrow (or repay) as part of the move. Understanding how the ported portion is treated, what happens to any additional borrowing, and whether any charges could apply will help you judge whether porting is likely to be the most suitable option for your circumstances.