Porting a Mortgage: How It Works, Lender Rules and When Not to Port

By Jake Stott, Knox Mortgages. Reviewed by an adviser authorised under Fort Advice Bureau, FCA FRN 972730. Published 25 September 2026. Last reviewed 25 September 2026.

Porting a mortgage means moving your existing mortgage deal, meaning its interest rate, end date and early repayment charge terms, from the home you are selling to the home you are buying, with the same lender. What moves is the product, not the loan. Your lender treats the new home as a fresh application and checks your income, credit and the property against its criteria as they stand today.

That distinction is where most porting plans go wrong. People assume porting is a formality because they already have the mortgage. It is not. Nationwide’s own guidance says porting “is not a transfer of the mortgage loan” and that you will have to reapply and meet its current lending criteria. If your income has dropped, you have gone self-employed, or the new property does not fit, the port can be declined, and you may still owe the early repayment charge. This guide covers what each major lender actually allows, with the numbers, and how to decide whether porting is even your best option.

What does porting a mortgage actually mean?

Porting a mortgage means your current lender lets you carry your existing fixed or tracker deal across to a new property instead of charging you an early repayment charge (ERC) for ending it early. The old mortgage is redeemed when your sale completes and a new mortgage account is opened on the purchase, carrying the same rate and the same product end date.

Three things move with a port: the interest rate, the date the deal ends, and the ERC schedule. Three things do not automatically move: the lender’s approval, the loan amount and the property’s acceptability. Each is reassessed.

There are three types of port. A like-for-like port keeps the same balance. A port with additional borrowing keeps your balance on the old deal and puts the extra on a new product. A partial port (borrowing less, usually when downsizing) moves part of the balance and repays the rest, which normally triggers an ERC on the part repaid.

Porting only exists with your current lender. If you want to move lender, that is a new purchase mortgage, and your ERC is payable in full.

Can I port my mortgage?

You can port your mortgage if your deal is marked as portable in your mortgage offer, you still meet your lender’s current lending criteria, and the new property is acceptable security. Most fixed and tracker deals from UK high street lenders are portable. Standard variable rate balances usually have no ERC to protect, so porting is irrelevant. Some specialist, offset and older products are not portable at all, so check the “portability” section of your offer before you put your house on the market.

The three tests the lender runs:

1. You. Income, outgoings, credit file and employment status, assessed against today’s criteria and today’s stress rate. What they accepted in 2021 does not bind them now.
2. The loan. Loan to value and loan to income on the new property. Moving to a more expensive home with a small deposit can push you into a loan to value band where the lender has tighter rules.
3. The property. Construction type, tenure, lease length, flats above commercial premises and properties with structural issues are all assessed on the valuation.

A port is approved only when all three pass. Failing one means either restructuring the application or looking at a different lender entirely.

Do you have to reapply when you port a mortgage?

Yes, in almost every case. Porting is a fresh application with your existing lender, including a valuation of the new property and, where you are borrowing more, a full affordability assessment. Nationwide states plainly that you will have to reapply for a new mortgage loan and meet its current lending criteria. HSBC says you need to meet its affordability criteria and the new property must meet its lending and valuation criteria.

There is one useful exception. NatWest’s intermediary porting criteria, checked in September 2026, state that a like-for-like or reduced-borrowing residential port does not need to pass affordability. NatWest defines like-for-like as the same or less borrowing, the same or a longer term, the same repayment type and the same applicants. Change any one of those and you are back to a full assessment.

The practical point: do not assume your current lender will say yes. Before you agree a sale, get a decision in principle on the port, or have a broker check it against your lender’s current criteria. Finding out after exchange that the port has been declined is the worst possible timing, because you are then committed to the purchase with no mortgage agreed.

What happens if I port my mortgage and borrow more?

If you port and borrow more, your existing balance stays on its current rate and end date, and the extra borrowing goes on a separate new product at today’s rates. You end up with one mortgage made up of two parts, each with its own rate and often its own end date. Barclays calls this a multi-part mortgage and notes the extra amount can even be repaid over a different term. Nationwide confirms the ported rate does not apply to the additional amount and that there is no ERC on the additional borrowing itself.

NatWest adds a threshold in its intermediary criteria: additional borrowing of £10,000 or more can go on its new business rates, but anything under £10,000 is placed on its standard variable rate. That matters if you only need a small top-up.

The additional borrowing always requires full affordability. You are asking the lender to lend more money, so income, commitments and credit are all checked, and the total loan must fit within its loan to income limits. Use our how much can I borrow guide to sense-check the total before you start viewing.

Worked example: porting and borrowing more (blended rate)

You own a home worth £300,000 with £180,000 outstanding on a 5-year fix at 3.99% that ends in March 2029. You are buying at £420,000 and putting in £120,000 of equity from your sale. You need a £300,000 mortgage.

Part	Balance	Rate	Annual interest (year one, simplified)
Ported part	£180,000	3.99%	£180,000 x 3.99% = £7,182
Additional borrowing (new 5-year fix)	£120,000	4.49%	£120,000 x 4.49% = £5,388
Total	£300,000		£12,570

Blended rate: £12,570 divided by £300,000 = 4.19%.

The catch is the end dates. Your ported part ends in March 2029, the new part in 2031. In 2029 you can only refix the smaller part without paying an ERC on the larger one, so you are locked in for longer than it looks. Some lenders let you choose a new product for the extra borrowing that ends at the same time as the ported part. Ask for that when it is offered, because it keeps your options open at the next review. (Rates are illustrative for the arithmetic, not a quote.)

Can I port my mortgage to a cheaper house?

Yes, but the part of the balance you repay is normally subject to your early repayment charge. When you downsize and borrow less, the lender ports what you still need and the difference is repaid on completion. Nationwide states that the difference must be repaid on completion and an ERC will apply to that amount. Santander says that if you borrow less, it will refund only part of the ERC.

Some lenders reduce the charge by your unused annual overpayment allowance. HSBC applies the ERC only to the reduction above your overpayment allowance, and its own example uses a £100,000 balance with a £10,000 allowance: porting £85,000 means an ERC on £5,000. NatWest’s intermediary criteria say the same thing: a partial ERC on the amount the borrowing is reduced by, less any overpayment allowance.

Worked example: partial port when downsizing

You owe £250,000 on a fix with a 3% ERC and a 10% annual overpayment allowance you have not used this year. The new home needs a £190,000 mortgage, so £60,000 is repaid.

Lender approach	Amount subject to ERC	ERC at 3%
ERC on the full reduction	£60,000	£1,800
ERC on the reduction less the overpayment allowance (10% of £250,000 = £25,000)	£60,000 minus £25,000 = £35,000	£1,050

If you have already used your allowance this year, the lower figure does not apply. If your ERC is a large sum, it can be worth using the allowance before the sale or keeping the extra equity as savings for a few months and overpaying later. Our early repayment charge guide explains how ERCs are calculated in more detail.

How long do I have between selling and buying to port?

It depends on the lender, and the windows are shorter than many people expect. If your sale and purchase complete on the same day, the port is continuous and there is no gap to worry about. If you sell first and buy later, most lenders charge the ERC when the old mortgage is repaid and refund it only if your new mortgage completes within their window. Some simply withdraw the right to port once the window passes.

Lender	Window after the old mortgage is repaid	Conditions and notes (checked September 2026)
Nationwide	180 days	If you cannot complete within 180 days of paying off your existing mortgage, the product and rate are lost and you cannot port
Barclays	180 days	No ERC as long as the new mortgage starts within 180 days of selling your current home
HSBC	6 months	ERC refunded if you apply and complete your new purchase within 6 months of the old mortgage being repaid
NatWest	4 months	Maximum 4 months from redemption to completion to be eligible for the ERC refund (intermediary criteria)
Santander	3 months (6 months for a new build)	ERC refunded within 4 weeks of the new mortgage starting if it is for the same amount or more. Flexible Offset customers who want to keep their rate must sell and buy on the same day
Halifax	Not published in a form we could verify	Halifax says there is no ERC if it agrees to port your deal. Confirm the refund window in writing before you exchange on your sale

Two practical warnings. First, if the ERC is deducted when your sale completes, you need to fund your move without that money until the refund arrives. Second, windows run from redemption, not from when you found a new house, so if you sell into rented accommodation, the clock starts on your sale completion date.

Worked example: the timing gap

You sell on 1 March and complete your purchase on 20 June, a gap of 111 days. That fits inside the windows at Nationwide (180 days), Barclays (180 days), HSBC (6 months) and NatWest (4 months, roughly 120 days). It misses Santander’s 3-month window on an existing home. A 111-day gap with a 3% ERC on £200,000 is £6,000 that you either get back or lose, depending entirely on which lender you are with.

Can I port a mortgage if I am in negative equity?

Sometimes, but it is the hardest type of port to get approved. Negative equity means you owe more than the home is worth, so when you sell, the sale price does not clear the mortgage. A normal port assumes your sale repays the old loan; with negative equity there is a shortfall that must either be paid from savings or carried across onto the new property.

A small number of lenders have negative equity porting policies for their own existing customers, allowing some or all of the shortfall to be moved to the new mortgage. These policies are narrow. They typically require a clean payment record on the existing mortgage, a maximum loan to value on the new property, full affordability on the total, and often no additional borrowing. They are reviewed often, so treat any lender name you see online with caution unless it is dated.

If your lender will not port negative equity, the realistic options are to clear the shortfall from savings, stay put until the balance falls or the value rises, or let the property and move, which is a different application altogether. Check the numbers with a broker before listing the house, because the gap between what you owe and what an agent says the house might fetch decides which route is open to you.

Can I port my mortgage if my circumstances have changed?

You can apply, but the lender assesses you as you are now, not as you were when you took the deal. Porting gives you no protection against changes in your income, job or credit since the original application. These are the four changes that most often cause problems.

Change since your last mortgage	How lenders treat it on a port	What usually fixes it
You went self-employed	Assessed as a new self-employed applicant. Many lenders want 2 years of accounts or SA302s; some accept 1 year	A lender that accepts 12 months of trading, or a like-for-like port where the lender does not re-test affordability. See our self-employed home movers guide
Lower income (part-time, maternity leave, career change)	Full affordability on any additional borrowing; may fail even for the existing balance at lenders that re-test	Borrow less, extend the term, or use NatWest-style like-for-like rules where available
Adverse credit since (defaults, CCJs, missed payments)	Scored against today’s credit policy. Missed payments on the mortgage being ported are the most damaging	A specialist lender may be better than the port. See our guide to a mortgage with defaults
Joint to sole, or adding a partner	Treated as a change of applicants: a like-for-like port no longer applies and full affordability is checked	The departing borrower’s written consent, plus sole affordability evidence

Age matters too. If you want to extend the term, the new term may now run past your retirement age, and the lender will want to see how the mortgage is repaid from pension income.

When is paying the ERC and remortgaging better than porting?

Paying the ERC and taking a new deal wins when your current rate is well above today’s rates and the ERC is small relative to the interest you would save. This is common for people who fixed in late 2022 or 2023 when rates peaked. Porting preserves your deal, but if the deal is expensive, preserving it costs you money.

Worked example: port vs pay the ERC

You owe £200,000. Your current fix is 5.49% with 2 years left and a 2% ERC. A new 5-year fix on the purchase is 3.89% with a £999 product fee.

	Keep the deal (port)	Pay the ERC and take a new deal
Upfront cost	£0	ERC £200,000 x 2% = £4,000, plus £999 fee = £4,999
Interest over 2 years (simplified)	£200,000 x 5.49% x 2 = £21,960	£200,000 x 3.89% x 2 = £15,560
Total cost over 2 years	£21,960	£15,560 + £4,999 = £20,559
Difference		£1,401 cheaper to pay the ERC

Now change one number. If your current rate were 4.49%, porting costs £17,960 over 2 years against £20,559 to switch, so porting wins by £2,599. The break-even is where the interest saving equals the ERC plus fees. (Simplified: interest-only maths ignoring capital repaid, which slightly reduces both columns.)

Also check whether your lender will waive the ERC if you take one of its new products for the move. Some high street lenders waive it for home movers when the existing deal is close to ending. Our guides to remortgaging and product transfers versus remortgaging cover the switch side of this decision.

Why do porting applications get declined?

Porting applications get declined for the same reasons any mortgage application does, plus a few that are specific to moving an existing deal. The table below covers the ones we see most and the fix for each.

Reason for decline	Why it happens	The fix
Affordability fails on the total loan	Additional borrowing pushes the loan to income past the lender’s cap, or today’s stress rate is higher than when you first borrowed	Reduce the extra borrowing, extend the term, or use a lender with a higher income multiple and pay the ERC if the numbers work
Income type no longer accepted	Now self-employed, contracting, or relying on bonus or overtime the lender discounts	Move to a lender whose criteria fit your income, or port like-for-like where affordability is not re-tested
Credit file has changed	New defaults, arrears, high card balances or a payday loan since the original application	Specialist lender, or wait and rebuild if the port can be timed later
Property is unacceptable	Non-standard construction, short lease, flat above a shop, ex-local authority tower block, structural issues on the valuation	Different property, or a lender with wider property criteria. See our non-standard construction guide
Timing window missed	Purchase completes after the lender’s port window	Negotiate completion dates before exchange, or plan the ERC as a cost
Product not portable	Some offset, specialist and older products cannot be moved	Treat the move as a new mortgage and budget for the ERC
Change of applicants	Removing or adding a borrower breaks the like-for-like definition	Full application with written consent from the departing party

Is porting worth it?

Porting is worth it when your current rate is lower than, or close to, what you could get today, your ERC is significant, and you still comfortably meet your lender’s criteria. It is not worth it when your rate is well above the market, when your lender’s criteria no longer suit your income, or when the multi-part structure locks you in with mismatched end dates.

The one question porting cannot answer on its own is whether your lender is still the best lender for you. Porting keeps you with the same bank by default. A whole-of-market broker checks the port against every alternative: the port, the port with a new product for the extra borrowing, the lender’s own home mover deals with an ERC waiver, and a full move to another lender with the ERC paid.

An illustrative Knox case

A couple in Stockport were moving from a £285,000 semi to a £410,000 detached home. They had £170,000 on a fix at 4.84% with 22 months left and a 3% ERC (£5,100). One of them had gone self-employed 14 months earlier. Their lender wanted two years of accounts before it would count that income, so the port with £95,000 of additional borrowing was going to fail on affordability.

We placed them with a lender that accepts one year of accounts for an established contractor moving into the same line of work. They paid the £5,100 ERC, but the new 5-year fix was 1.05% lower than the old deal on the ported portion, which recovered the ERC in under three years, and they moved on schedule. Porting would have cost them the purchase. (Illustrative case with details changed to protect client confidentiality.)

If you are planning a move, our home mover mortgage page covers the wider process, including how to time your sale and purchase.

How do I port my mortgage? Step by step

1. Read your mortgage offer. Check that the product is portable, note the ERC percentage, the product end date and the overpayment allowance.
2. Get your redemption figure. Ask your lender for the current balance and ERC in pounds.
3. Check your lender’s port window and whether the ERC is deducted and refunded, or waived at source.
4. Get a decision in principle on the port before you accept an offer on your sale, including any additional borrowing.
5. Compare against the market. Run the port vs pay-the-ERC maths above with real rates.
6. Apply once you have an accepted offer on the new home. The lender values the property and underwrites the case.
7. Line up completion dates so the gap between sale and purchase sits inside the window, ideally on the same day.

Porting has no effect on stamp duty. You pay stamp duty on the purchase price of the new home exactly as you would with a brand new mortgage.

Porting a mortgage: frequently asked questions

What does porting a mortgage mean?

Porting a mortgage means moving your existing mortgage deal, including its rate, end date and early repayment charge terms, to a new property with the same lender. The lender does not simply transfer the loan: it reassesses your income, credit and the new property against its current criteria before it approves the port.

Can I be refused a mortgage port?

Yes. Your lender can decline a port if you no longer meet its current lending criteria, if the new property is not acceptable security, or if additional borrowing fails affordability. Porting rights in your offer are conditional. Being an existing customer does not guarantee approval, which is why you should check the port before you agree your sale.

Do I pay an early repayment charge if I port my mortgage?

No, if the port is like-for-like or you borrow more and it completes within your lender’s window. Yes, on the amount you repay, if you borrow less. Many lenders charge the ERC when your sale completes and refund it once the new mortgage starts, so you may need to fund the gap.

How long does it take to port a mortgage?

Typically 2 to 6 weeks from application to mortgage offer, similar to a new purchase mortgage. The lender needs a valuation, and additional borrowing needs full underwriting. The overall move then depends on the conveyancing chain, which is usually the slower part.

Can I port my mortgage and borrow more?

Yes, if you pass affordability on the total. Your existing balance stays on its current rate and the extra goes on a new product at today’s rates, creating a two-part mortgage with a blended rate. NatWest puts additional borrowing under £10,000 on its standard variable rate, so small top-ups need checking.

Can I port my mortgage to a cheaper house?

Yes. You port the amount you still need and repay the rest, which is normally subject to your ERC. HSBC and NatWest reduce the charged amount by any unused overpayment allowance; Nationwide says an ERC applies to the difference. Using your overpayment allowance before the sale can cut the cost.

Can I port my mortgage if I sell before I buy?

Yes, within your lender’s window. As of September 2026 that is 180 days at Nationwide and Barclays, 6 months at HSBC, 4 months at NatWest and 3 months at Santander (6 months for a new build). Miss the window and you lose the deal or the ERC refund.

Can I port my mortgage to a buy-to-let or keep my home and let it?

Not usually. A port moves a residential deal to your next residential home. If you want to keep your current home and let it, you need consent to let or a buy-to-let remortgage on that property, plus a new residential mortgage on the purchase. That is a let to buy arrangement, not a port.

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