Porting a mortgage means taking your existing rate and product terms with you when you move home. Secured a competitive fixed rate and want to buy elsewhere? Porting could let you keep it, rather than giving it up for today’s rates.

What Does Porting a Mortgage Mean?

Despite the name, nothing simply moves from one property to the other.

Your current mortgage gets repaid when you sell. Your lender then issues a new one, secured against the property you’re buying and carrying across the existing product and rate, provided they approve the new application.

That approval matters. Portability is a feature of the deal, not an automatic right to borrow again. Your lender still assesses your current income, spending and overall affordability, and checks that the new property meets its lending criteria. FCA rules require lenders to assess affordability for regulated mortgage contracts.

Many fixed-rate mortgages from major lenders, Nationwide, Halifax and Barclays among them, can be ported, though the rules vary between lenders and products. Check your original mortgage offer or product documents. Don’t assume the option is there.

How Does Porting a Mortgage Work?

Here’s how it usually goes:

1. Check your original mortgage offer or product documentation to confirm that your deal is portable.
2. Speak to your existing lender or mortgage adviser about the new property and the amount you need to borrow.
3. Apply for a Decision in Principle based on your current circumstances.
4. Submit the full mortgage application.
5. The lender reassesses your income, expenditure, credit position and affordability.
6. A valuation is carried out on the new property.
7. If everything is approved, the lender issues a new mortgage offer that carries across your existing product rate.
8. Your solicitor repays the old mortgage and draws down the new one when the sale and purchase complete.

Completing the sale and purchase on the same day is the simplest route, but not essential. Some lenders allow a gap and refund the Early Repayment Charge if the new mortgage completes within a set window. Nationwide currently allows up to 180 days in qualifying cases. Halifax confirms no ERC is due if you borrow the same amount or more when porting, though a refund on other scenarios is not guaranteed and depends on your circumstances.

There’s no universal timescale. A straightforward application can move quickly. Valuation delays, affordability questions or a snag elsewhere in the chain can just as easily slow it down.

Who Is Eligible to Port a Mortgage?

Lenders treat porting much like any new mortgage application. This catches plenty of people off guard.

Your income and expenditure get assessed as they stand now, not as they looked when you first took the mortgage out. A lower income, larger credit commitments or higher household costs could all reduce what you can borrow. Recent arrears or other credit problems may affect the decision too.

The new property has to meet the lender’s criteria too. Non-standard construction, flats above commercial premises and short leases can all cause problems, depending on the lender and the property itself.

Joint borrowers still need to qualify together. Add someone to the mortgage, or remove an existing borrower, and the application gets more involved. The lender has to assess the new borrowing and ownership arrangement from scratch.

Moving to a cheaper property can also mean a partial port. You take only the amount you still need, and the rest of the existing mortgage gets repaid. An Early Repayment Charge may then apply to the part you leave behind. Nationwide, for example, confirms an ERC may be charged on the balance that isn’t ported.

Porting to a More Expensive Property

Buying a more expensive home usually means borrowing more.

The balance you port keeps its existing rate for the rest of that product period. Any additional borrowing normally sits on a separate sub-account, on one of your lender’s current products. That rate may land higher or lower than the one you’re porting.

The lender assesses both parts together. So even if the original balance looks perfectly affordable on its own, the whole application can still be declined if the combined borrowing doesn’t pass the lender’s checks.

You may also end up with two rates and two different deal end dates. Port £150,000 at 2.1%, say, while borrowing another £40,000 at 5.4%. Both amounts sit under the same mortgage. But they carry different monthly costs and may need reviewing at different times.

It is manageable. But it needs planning.

Porting to a Cheaper Property

Move to a cheaper property and you can only port the amount you still need to borrow. Any surplus gets repaid when the old mortgage is redeemed.

If you’re still within a fixed or discounted deal, the lender may charge an Early Repayment Charge on the part you don’t port. ERCs often fall between 1% and 5% of the amount repaid early, though the percentage and calculation depend entirely on your mortgage product. Check your mortgage offer or latest statement for what applies to you.

The new mortgage must also fit the lender’s permitted loan-to-value range. A cheaper property doesn’t automatically mean a lower LTV. What you’re borrowing matters just as much as the purchase price.

Negative equity will usually stop a standard port. The sale simply doesn’t generate enough to repay the existing mortgage. You’d need to cover the shortfall, or find another route, before the move could go ahead.

A deposit may still be required. Suppose you sell for £250,000 with £180,000 left on the mortgage. That gives you £70,000 before estate agent, legal and moving costs. You then buy for £230,000. If the lender allows a maximum 75% LTV, the largest mortgage would be £172,500, so you would need a £57,500 deposit. That leaves £12,500 of the sale proceeds before the other costs of moving are taken into account.

Benefits of Porting a Mortgage

The biggest advantage is keeping a low fixed rate when new mortgage rates are higher.

Porting may also help you dodge some or all of the Early Repayment Charge on your existing deal. On a £200,000 balance with a 3% ERC, the full charge would be £6,000.

You also stay with a lender you already know. That doesn’t remove the application, valuation or legal work, but it can make the product side of the move feel more familiar.

Disadvantages of Porting a Mortgage

Porting is not automatically the cheapest choice.

If rates have fallen since you fixed, keeping the old one could mean paying more than a new deal would cost. And if you need additional borrowing, your lender’s top-up rate may be less competitive than what’s available elsewhere.

Affordability is the other risk. Your deal may be portable on paper, but the lender can still decline the new application. If that happens, you might end up moving to another lender anyway and paying the ERC on your existing mortgage regardless.

This is why checking affordability early matters. A Decision in Principle isn’t a guarantee, but it gives you a clearer read on whether the figures work before you exchange contracts and become legally committed.

There’s also the admin of managing separate mortgage parts. Different rates and end dates can leave you reviewing one section while the other’s still locked into a fixed deal.

Once your fixed rate has ended, there’s often little benefit left in porting. No fixed product to preserve, usually no ERC to avoid. Comparing remortgage options across the market tends to make more sense at that point.

Mortgage Porting vs Remortgaging: Which Costs Less?

You need to compare the full cost of both routes, not just the headline rates.

Total cost of porting: the cost of the retained rate on the ported balance, plus the cost of any additional borrowing at your lender’s current rate, together with any product, valuation or legal fees.

Total cost of remortgaging: the cost of the new rate across the full mortgage, plus any Early Repayment Charge, arrangement fee, valuation fee and legal costs.

When the ERC outweighs the saving from switching lenders, porting usually comes out ahead.

Here’s a simplified interest-only example. On a £200,000 balance with two years left at 2.5%, the interest over those two years would be around £10,000. At 4.5%, it would be around £18,000. Leaving the original deal would also trigger a 3% ERC of £6,000. In that example, porting is clearly cheaper.

A repayment mortgage needs a more detailed calculation, since the balance falls every month. The remaining term, repayment basis, fees and any additional borrowing all affect the result.

The answer flips when rates move in your favour, the ERC is nearly finished or your lender’s top-up rate is poor.

How Much Does It Cost to Port a Mortgage?

Lenders don’t usually charge simply for porting the rate. Moving home still comes with costs, though.

• Valuation fee: Often £250 to £500 for a standard residential property, although some mortgage products include a free valuation.
• Conveyancing costs: Usually around £1,000 to £2,500 for a standard residential purchase in England, depending on the property, location and complexity of the transaction.
• Early Repayment Charge: If you move to a cheaper property and do not port the full balance, an ERC may apply to the amount you repay.
• Arrangement fee: Additional borrowing may come with a product or arrangement fee.
• Stamp Duty Land Tax: Porting does not reduce the SDLT due on the new purchase. The tax is based on the property transaction and your circumstances, not on whether you keep your existing mortgage rate.

When Does Porting a Mortgage Make Sense?

Porting is worth considering when your fixed rate sits comfortably below what’s available now and you’ve still got a meaningful Early Repayment Charge period left.

It works best, too, when your circumstances are stable, the property meets the lender’s criteria and you’re not borrowing so much more that the top-up rate wipes out the benefit.

Remortgaging may make more sense when current rates undercut your existing deal, your ERC has ended or the additional borrowing tips things towards another lender.

The closer you get to the end of the deal, the less valuable dodging the ERC becomes. At that point, comparing your lender against the wider market matters more.

Buy-to-let mortgages play by different rules, and portability isn’t available on every product. Some buy-to-let mortgages also sit outside FCA regulation, depending on the circumstances. Worth speaking to someone who knows that corner of the market.

Not Sure Whether to Port or Remortgage?

Porting can save you thousands. It can also leave you tied to a lender whose top-up rate no longer stacks up.

At Mortgaged, we can run both options properly. Your existing rate, Early Repayment Charge, additional borrowing and the wider mortgage market all go into the calculation. With more than 120 lenders to draw on, you see what the move actually costs instead of guessing.

Get in touch today and we’ll help you work out which route makes sense.