What Is Mortgage Porting?
Porting means taking your existing mortgage product - including its interest rate, terms, and outstanding balance - and applying it to a new property rather than paying off the mortgage when you sell and taking out a completely new one. It is available at the discretion of the lender - there is no legal right to port a mortgage - and the new property must meet the lender's security requirements.
When Porting Makes Financial Sense
Porting is most beneficial when: you are in a fixed-rate deal with a significant early repayment charge (ERC) and the current market rate for a new mortgage is higher than your existing rate; the time remaining on your fixed period is short enough to make the ERC meaningful; and the new property meets your lender's security criteria. In this scenario, porting avoids the ERC while keeping a below-market rate.
The Practical Process
Porting is not automatic - the lender must approve the new property as security and must re-underwrite your affordability based on your current income and financial position. If your income has changed since the original mortgage, if you have taken on additional debt, or if your credit profile has changed, the re-underwriting could result in the lender declining to port even where the new property is perfectly acceptable. You are effectively making a new mortgage application on your existing product.
Topping Up When Porting
If the new property costs more than your existing property (after selling), you need additional borrowing - a top-up - on top of the ported amount. The top-up is typically at the current market rate (not your ported rate), creating a blended rate across two loans with two end dates. This is often the main complication of porting - managing two mortgage parts with different rates and terms simultaneously.
When Not to Port
Porting does not make sense when: the early repayment charge is small relative to the saving from switching to a better market rate; the new property does not meet the existing lender's criteria; the top-up required is large and at a significantly higher rate than the ported balance; your circumstances have changed in a way that makes re-underwriting difficult; or the best deal on the market would save more than the ERC cost.
The Alternative: Pay the ERC and Remortgage
In some cases, paying the ERC and taking a new mortgage on the new property at the best available market rate is financially superior to porting. The break-even calculation compares the ERC cost against the interest saving from switching to a better rate over the remaining fixed period. A broker can model this comparison precisely.