Porting Your Mortgage When You Move.

How to take your existing deal with you — and what happens when the numbers don't add up.

Porting means transferring your existing mortgage deal to a new property when you move home. In principle it sounds straightforward — you keep your rate, avoid early repayment charges, and carry on. In practice, porting involves a full new mortgage application, affordability reassessment, and sometimes two separate products running simultaneously. This guide explains how it works and when it makes sense.

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1

What porting actually means

When you port a mortgage, you are not literally moving the same loan to a new property. You are applying to your existing lender to borrow on the new property under the same interest rate and terms as your current deal. The lender agrees in principle to honour the existing rate — but they still conduct a full underwriting assessment on you and the new property, exactly as if it were a new application.

This means porting can be refused. If your financial circumstances have changed since you took out the original mortgage — lower income, new credit commitments, a change in employment status — the lender may decline. Similarly, if the new property does not meet their lending criteria (unusual construction, short lease, above-a-shop location), they may refuse the port even if your finances are unchanged.

2

When you are borrowing more

If your new property costs more than your existing mortgage balance, you need to borrow the difference. Most lenders handle this by running two products simultaneously: the ported amount continues on the existing rate and terms, while the additional borrowing is offered on a new product at current market rates.

This creates a blended rate position. For example, if you are porting £200,000 at 1.9% and borrowing an additional £100,000 at 4.5%, your effective overall rate is approximately 2.77%. Whether this is competitive depends on what is available on the open market. A whole-of-market broker can run the comparison across both options — porting plus top-up versus a full remortgage to a new lender — and quantify the difference in total cost.

3

When you are borrowing less

If your new property is cheaper than your existing mortgage balance, you need to repay the difference on completion of your sale. This partial repayment is almost always subject to early repayment charges (ERCs) — even though you are porting the remainder. Lenders treat the repaid portion as an early redemption.

On a £300,000 mortgage with a 2% ERC, repaying £50,000 early costs £1,000. This is an unavoidable cost of downsizing during a fixed-rate period, and it should be factored into your moving budget before you commit. In some cases — particularly when the ERC is large and the remaining fixed-rate term is short — it may be worth waiting until the deal ends before moving.

4

When lenders refuse a port

Lenders are not obliged to honour a port even if the mortgage documentation says porting is permitted. Common reasons for refusal include: the new property does not meet current lending criteria, affordability has worsened since the original application, the mortgage was taken out under a product that has since been withdrawn from the lender's range, or the lender's appetite for certain property types has changed.

If your port is refused, you face a full early repayment charge to exit the current deal — unless you can time your move to coincide with the end of the fixed-rate period. This is a scenario where taking broker advice before you exchange contracts is critical. Finding out the port will be refused after you have exchanged leaves you with limited and expensive options.

5

The timing challenge

Porting requires your sale and purchase to complete simultaneously, or within a short window permitted by the lender (typically 30–90 days). If your sale completes before your purchase, your mortgage is technically redeemed — and with it, your right to port. Some lenders allow a brief window to reinstate the port, but this varies and cannot be relied upon.

Chain delays are the most common cause of porting complications. If your buyer’s lender is slow, your purchase falls through and must be replaced, or your vendor pulls out, the porting window may close. Having a broker who understands the timing mechanics — and who can negotiate with the lender on your behalf — significantly reduces the risk of losing the ported rate through circumstance rather than choice.

6

Is porting always the right choice?

Not always. If current market rates are significantly lower than your existing rate — which can happen when rates have fallen sharply since you took out your mortgage — paying the ERC and remortgaging to a new lender may be cheaper in total over the remaining term. This is a calculation, not an assumption.

Your broker should model both scenarios: the total cost of porting (including any top-up product and partial ERC if applicable) versus the total cost of full redemption plus a new mortgage on the open market. The answer is rarely obvious without running the numbers.

What to remember from this guide.

Porting still requires a full new mortgage application — it can be refused even if your existing deal allows it
Additional borrowing runs on a separate product at current rates, creating a blended overall rate
Partial repayments when downsizing are usually subject to early repayment charges
Sale and purchase must complete simultaneously or within the lender's porting window — chain delays are a real risk
Always model porting versus full remortgage to a new lender — porting is not automatically the cheapest option