Porting Your Mortgage When You Sell: 2026 UK Seller Guide

By Lisa Hayes · 20 September 2026

Yes, in most cases you can port your mortgage when you sell, but porting is a product feature rather than a legal right, and your lender will underwrite you from scratch before agreeing to it. You keep your existing interest rate on the balance you carry across, and the early repayment charge is waived or refunded provided the new purchase completes inside your lender's porting window. The catch is that a port is approved on today's affordability rules, not the ones that applied when you first borrowed.

If you are sitting on a fix taken out in 2021 or 2022 at 1.6% and you are about to sell, that rate is the single most valuable thing you own after the house itself. Losing it by accident, because nobody told you the port had to be applied for before you accepted an offer, is a genuinely expensive mistake. This guide covers the whole picture: how porting actually works mechanically, what it costs, when it fails, and what to do when it does.

What does porting a mortgage actually mean?

Porting sounds like your mortgage picks itself up and walks to the new address. It does not. What actually happens on completion day is that your existing mortgage is redeemed in full from the sale proceeds, and a completely new mortgage is created against the new property, secured by a new legal charge at HM Land Registry. Your lender then applies your existing product — the rate, the remaining fixed term, the end date — to that new loan.

The distinction matters because it explains almost everything else in this guide. If it were a genuine transfer, your lender could not re-underwrite you. Because it is a new loan, they can, and they do. Full affordability assessment. Fresh credit search. New valuation on the property you are buying. Your twelve years of perfect payments buy you goodwill and nothing more.

It also explains why the early repayment charge question is fiddly. You are technically repaying the mortgage early, which is exactly the event an ERC exists to penalise. Lenders get around this by either waiving the charge where both transactions complete on the same day, or charging it on the sale and refunding it when the purchase completes inside the porting window. Which of those two applies to you is a question worth asking your lender in writing, because it changes how much cash you need available on the day.

Is porting a right, or something my lender can refuse?

It is a contractual feature of your mortgage product, and it comes with conditions. Check your original mortgage offer — the document with the Key Facts Illustration or European Standardised Information Sheet attached. Somewhere in there is a line confirming whether the product is portable. Almost all residential fixed and tracker products from mainstream lenders are. Some specialist, adverse-credit, and older discounted products are not.

Portable does not mean guaranteed. The standard wording gives the lender the right to decline the new lending on normal underwriting grounds, which is a very wide door. The Financial Ombudsman Service takes the view that a lender is generally entitled to apply its current lending policy to a port, so complaining after a refusal rarely succeeds unless the lender misled you about the process or handled it badly.

Do my sale and purchase have to complete on the same day?

Usually, yes. The tidiest version of a port is a simultaneous exchange and completion: your buyer's money arrives, your old loan is redeemed, the new advance is drawn down, and everything settles within a few hours. Your solicitor handles the choreography. No ERC is charged because the lender treats the whole thing as one continuous arrangement.

This is also why porting adds pressure to a chain. Your ported mortgage offer will have an expiry date, typically three to six months from issue. If the chain drags and the offer lapses, you are re-applying, and re-applying means being re-assessed on whatever the lender's policy looks like that month. Anyone who has watched a chain collapse at the last minute knows how quickly a comfortable timetable becomes a scramble.

What if I sell now and buy later?

This is where the porting window becomes the most important number in your file. If your sale completes and your purchase does not, your lender charges the ERC on redemption and then refunds it if you complete a new purchase with them inside a set period.

Those windows vary more than most people expect. Nationwide, for example, publishes a 180-day window for a full refund. Other lenders work to 90 days. A handful stretch to six months, and at least one building society offers twelve months where a legacy scheme applies. Nobody should be guessing here: phone your lender, ask for the exact number of days and whether it runs from completion of the sale or from redemption of the account, and ask them to confirm it in writing or on a recorded call.

Two things to plan for if you take this route. First, you will need the ERC in cash on completion day — it comes out of your sale proceeds, so your equity is temporarily lighter than you budgeted. On a £180,000 balance with a 3% charge, that is £5,400 sitting with your lender until the refund lands. Second, if you rent in between, your lender's affordability assessment will now include that rent as an outgoing. Sellers who go into rented to break a chain occasionally discover that the rent they are paying is the reason they can no longer afford the mortgage they already had.

Will I still pay an early repayment charge?

On the balance you carry across, no, assuming you complete in time. ERCs on UK fixed-rate products typically run between 1% and 5% of the outstanding balance, usually stepping down by one percentage point per remaining year of the fixed term. Our full guide to early repayment charges when you sell goes through the arithmetic in detail.

You can still get caught out in two situations. One is the timing gap described above. The other is downsizing, covered further down, where the portion of the loan you are not carrying across is treated as an early repayment and charged accordingly.

What does porting a mortgage cost in 2026?

Porting the balance alone is often close to free. The costs appear as soon as you borrow more, and they are easy to underestimate.

Set that against what you are protecting. With the Bank of England base rate held at 3.75% on 17 September 2026 and the average two-year fix sitting around 5.7%, a borrower carrying a 1.8% fix on £200,000 with two years left is protecting roughly £7,800 a year in interest. That is the number that should drive your decision, not a £300 valuation fee.

Port or break? How to work out which is genuinely cheaper

Do not assume porting wins. It usually does when you are on an old cheap fix with meaningful time left. It often loses when your fix is nearly over, or when your lender's current rates are uncompetitive and you are being forced to take the top-up borrowing from them.

Work it out like this, in pounds, over the remaining fixed term:

1. Cost of porting. Interest on the ported balance at your old rate, plus interest on any additional borrowing at your lender's current rate, plus fees.
2. Cost of breaking. The ERC, plus interest on the whole new loan at the best rate available to you on the open market, plus fees.
3. Compare the totals. Not the monthly payments. The totals over the same period.

The trap is step one. If you are porting £120,000 at 1.8% and borrowing another £180,000 from the same lender at 5.9% because that is their only option, your blended rate is about 4.26%. A whole-of-market lender offering 5.2% on the full £300,000 may well beat it once you allow for the ERC being a one-off and the rate difference being annual. Run the numbers. A broker who only wants to port because it is less work is not serving you.

What happens if I need to borrow more?

Most lenders allow it, and the mechanics are consistent across the market. Your existing balance keeps its rate and sits in one sub-account. The additional borrowing goes into a second sub-account on a product chosen from your lender's current range. You end up with one mortgage, two rates, two end dates, and one direct debit.

The two end dates are the part that quietly costs people money. If your ported portion runs out in March 2028 and your top-up runs to September 2030, you cannot remortgage the whole lot in 2028 without paying an ERC on the top-up. You are locked to that lender until the later date, and they know it. Ask for the additional borrowing product to be aligned to your existing end date. Many lenders offer a short-term or bespoke-length product precisely for this. Some will not, and that is useful information about whether to port at all.

Affordability on the top-up is assessed on the whole debt, not just the new slice. That surprises people who reason that they were approved for £200,000 in 2021 so £240,000 should be fine now. Lender stress tests, childcare costs, car finance taken out since, and a student loan deduction all land on the same spreadsheet.

What if I'm downsizing and need a smaller mortgage?

Here is the trap almost nobody is warned about. You are porting £180,000 down to a £120,000 mortgage on a smaller house. The £60,000 you are not carrying across is, from the lender's perspective, an early repayment. Your annual overpayment allowance — usually 10% of the balance, so £18,000 — absorbs part of it. The remaining £42,000 is charged at your ERC rate. At 3%, that is £1,260 you did not budget for.

Some lenders are more generous and waive the charge entirely where the reduction is caused by a genuine downsize. Others apply it strictly. Nobody advertises which camp they are in. This is a direct question to ask before you list: "If I port and reduce my balance by £60,000, will you charge an ERC on the reduction, and how much?"

There is a second consideration for downsizers. A small ported mortgage at 1.8% over a short remaining term saves real but modest money, and the flexibility of being with a lender of your choosing may be worth more. If you are working through the wider downsizing decision, treat the port as one input rather than the deciding factor.

Why do lenders turn porting applications down?

In rough order of how often they bite:

• The property. Your lender's current policy may exclude the thing you are buying. Flats above commercial premises, short leases, non-standard construction, properties with cladding issues, anything a surveyor flags as difficult to sell. You can be a perfect borrower and still fail because the security is wrong. If you have any doubt, read our guide to what makes a property unmortgageable and check before you offer.
• Affordability. Income has fallen, a business has had a weaker year, a partner has gone part-time, or commitments have grown. Lender criteria also tighten and loosen independently of you.
• Credit conduct. Missed payments on the mortgage itself are the fastest way to void portability. Defaults, a recent payday loan, or heavy use of buy-now-pay-later all show up.
• A down valuation. If the surveyor comes in below the price you agreed, the loan-to-value moves and the port may no longer fit the product. Our guide to handling a down valuation covers the challenge process.
• Age at end of term. Porting a 25-year term onto a new property in your late fifties can breach maximum-age-at-expiry rules that did not bite last time.

My port has been declined. What are my options?

Order of attack:

1. Find out precisely why. "Affordability" is not an answer. Was it the debt-to-income ratio, the stress-tested payment, the property, the valuation, the term? The specific reason determines whether it is fixable.
2. Ask about a product transfer instead. Staying with your lender on a different product sometimes clears criteria that the port did not, particularly where the sticking point was the product's maximum LTV rather than your income.
3. Go whole-of-market. Criteria differ enormously between lenders on self-employment, bonus income, contractors, flats, and construction types. The FCA's modified affordability assessment rules also give lenders room to help borrowers who are up to date but would fail a standard test. A decline from one lender is not a verdict from the market.
4. Reduce the borrowing. A larger deposit or a cheaper property changes the arithmetic immediately.
5. Extend the term. Unglamorous, effective, and it cuts the stress-tested monthly figure.
6. Reconsider the purchase, not the sale. If your sale is solid and only the onward purchase has failed, selling and renting keeps your buyer and buys you time — inside the porting window, ideally.

Which situations make porting harder than people expect?

Divorce and separation

If one party is keeping the mortgage and the other is being removed, that is a transfer of equity plus a port, assessed on one income. Two underwriting hurdles at once, in the middle of an emotionally difficult sale. Our guides on selling during divorce and removing a name from a joint mortgage cover the sequencing.

Interest-only mortgages

Porting an interest-only balance usually requires you to evidence a credible repayment vehicle under today's rules, which are much stricter than they were pre-2014. Expect a fight, and expect part of the balance to be pushed onto capital repayment.

Help to Buy and shared ownership

Both add a third party. With Help to Buy you are repaying or porting alongside the equity loan, which needs its own valuation and administrator approval. Shared ownership ports are restricted to a small pool of lenders and a smaller pool of products.

Let to buy

Keeping your current home and letting it out while buying another is not porting. It is a consent-to-let or a remortgage to buy-to-let plus a new residential mortgage. If you are weighing this up, sell or rent it out sets out the numbers properly.

Negative equity

If you owe more than the house is worth, porting is off the table in the ordinary sense. A small number of lenders operate negative equity transfer schemes; most do not. Read selling in negative equity before you speak to anyone.

What order should I do all this in?

Most people get this backwards. They accept an offer, find a house, and then ring the lender. By then the timetable is set by other people.

1. Before you list: dig out your mortgage offer and confirm the product is portable. Find your ERC percentage and its expiry date. Ring your lender for the porting window in days.
2. Before you list: get a decision in principle for the port, including any additional borrowing. You will not know the property yet, but you will know whether the income side works. This is the single most valuable hour you will spend.
3. When you accept an offer: tell your lender or broker the same week. Do not wait for the survey.
4. When your offer on a new property is accepted: submit the full port application immediately. Valuation is the long pole.
5. Through conveyancing: keep your solicitor and lender talking. The redemption statement and the new advance have to land on the same day. See the conveyancing process for how the pieces fit.
6. Exchange and completion: ideally simultaneous on both transactions. Exchange versus completion explains why the gap between them matters.

If you are buying and selling together, the coordination problem is bigger than the porting problem. Selling and buying at the same time is worth reading alongside this.

What happens to my port if the chain collapses?

If your buyer pulls out before exchange, nothing happens to your mortgage — you have not redeemed anything. Your ported offer sits there until it expires, and you can usually get it extended once.

If the chain fails after your sale has completed but before your purchase does, you are inside the porting window and on borrowed time. This is the scenario where sellers make expensive decisions quickly. Some take a bridging loan, which is fast and costly. Others accept a lower, certain offer from a cash buyer to keep the sale alive rather than start again on the open market.

Which brings up the honest point about certainty. Around 30.3% of mortgage advances in the first quarter of 2026 went to home movers, according to FCA lending statistics, and every one of those transactions depended on a chain of other people's finances holding together. If your port is the fragile link, or if your buyer's mortgage is, speed matters more than the last few thousand pounds on the price. Some sellers in that position look seriously at cash house buyers or a supported sale because a guaranteed completion date is worth paying for. Others hold firm on the open market. Both can be right. What is never right is finding out on day 170 of a 180-day window that you have no plan.

The short version

Porting protects an asset most sellers do not think of as an asset. Treat your fixed rate like equity: know what it is worth, know the rules that govern it, and find out whether you qualify before you let anyone put a board outside your house. Ring your lender this week, ask for the porting window in days and the ERC in pounds, and write both numbers down.

And if the sums point towards a faster, more certain exit rather than a long chain, it is worth knowing what a genuine cash offer on your property looks like before you decide. You can compare offers with no obligation and see how the two routes stack up side by side. No pressure, no commitment, just the numbers in front of you.