"Porting" means keeping your current mortgage deal, rate and terms, and moving them to a new property. It sounds like a formality, but it isn't — you have to fully reapply and pass affordability checks again, using today's rules, on today's income. If you're borrowing more, the extra amount typically comes as a separate loan at current rates alongside your ported balance.
What porting actually means
When your mortgage deal is "portable" (most standard fixed and tracker deals are, but not all — check your offer or ask your lender), you can, in principle, transfer the same rate and terms to a new property when you move, rather than closing out your current deal and starting a new one.
The appeal is obvious if you're partway through an attractive fixed rate: keeping it avoids paying an early repayment charge (ERC) to exit early, and avoids losing a rate that might be well below what's currently on the market.
Even if your mortgage is technically portable, your lender has the final say and there's no guarantee they'll approve it. You're effectively submitting a brand new mortgage application — full income verification, credit checks and a valuation on the new property — under whatever the lender's current criteria are, which may be stricter than when you first borrowed.
How porting works if you need to borrow more
Moving to a more expensive property usually means borrowing more than your current balance. In this case, porting typically works as two linked parts:
- Your existing balance moves across at your existing (often lower) rate.
- The additional amount you need is a new, separate loan at whatever rates the lender is currently offering.
Worked example: your current deal has two years left at 4%. Your home is worth £300,000 with £180,000 outstanding (60% LTV). You sell for £300,000 and buy for £400,000. The £180,000 ports across at 4%, and you take a new £100,000 top-up loan at the lender's current rate for that portion — giving you a blended rate across the two, rather than the whole £280,000 at one single rate.
If you're moving to a cheaper property
Porting can work particularly well here — since you need to borrow less, not more, you may be able to reduce your monthly payments while keeping your existing rate, with no new borrowing to arrange. Just watch your loan-to-value: if your new mortgage is a much smaller percentage of the new property's (lower) value, your LTV improves, which can occasionally open up better options than staying on your existing deal at all.
If you're in negative equity
Most lenders won't allow porting if your current property is worth less than your outstanding mortgage balance, since there's a shortfall to account for when the sale completes. Some lenders will consider transferring the negative equity portion onto the new property on a case-by-case basis, but this is the exception rather than the rule. If this applies to you, speak to your lender or a broker early — being upfront about the situation gives you more options than discovering it partway through a sale.
When starting fresh beats porting
- Your current rate isn't actually that competitive — if the market has moved and better deals are available, there's no reason to protect a rate that isn't saving you anything.
- Your income or circumstances have changed in a way that makes porting's fresh affordability check risky — sometimes a different lender's criteria suit your situation better than your existing one's.
- You want to borrow significantly more — a blended rate across a ported balance and a new top-up loan can sometimes work out less competitive than simply remortgaging the whole amount fresh with a lender offering strong rates at your new LTV.
Practical steps if you're planning a move
- Speak to your lender or a broker before you list your home — find out whether your deal is portable and get an early read on your borrowing capacity under today's rules.
- Get an Agreement in Principle — this shows sellers and agents you're a serious, ready buyer, and flags any affordability issues before you're deep into a chain.
- Compare the ported + top-up route against a full remortgage side by side, including all fees, before committing either way.
- Keep timing in mind — porting still needs to complete around your sale and purchase dates, so build in the same lead time you would for any mortgage application.