Porting a mortgage transfers your existing mortgage product — including the interest rate and remaining fixed or tracker period — to a new property when you move. While most UK mortgage products are described as portable, porting is not guaranteed: your lender must re-approve your affordability against current criteria and the new property must meet their lending requirements.
| Key fact | Detail |
|---|---|
| Is porting guaranteed? | No — lender must approve the new application even if the product is portable (Source: FCA MCOB 11) |
| Re-affordability check | Full affordability re-assessment required including stress testing at current rates |
| ERC if refused | If lender refuses the port and you must redeem, early repayment charge applies |
| Additional borrowing | Any top-up above your existing balance is typically on a new product at current rates |
| Timing risk | Port must complete simultaneously with sale — missing this window can trigger ERC |
How Porting Works in Practice
When you port, you are not literally moving your existing mortgage — you are redeeming it on your old property and taking a new mortgage on your new property at the same rate and terms. The lender grants you a port window (typically 3-6 months) during which you can redeem without paying an ERC, provided you simultaneously complete on a new purchase with them on equivalent terms.
This means porting is essentially a new mortgage application. The rate is reserved, but everything else — affordability assessment, property valuation, legal work — starts again. Your circumstances must satisfy the lender's current lending criteria, which may be stricter than when you originally applied.
The Re-Affordability Check — Why You Can Be Refused
Under FCA MCOB 11, lenders must conduct a fresh affordability assessment on a port as if it were a new application. This means:
- Your income is re-verified — if your earnings have fallen since the original mortgage, you may not qualify for the same amount
- Your commitments are re-assessed — new car finance, childcare costs or other debts since your original application reduce affordability
- Stress testing applies — your payments are tested at your current rate plus 3% under current FCA guidance
- Your credit file is re-checked — any adverse credit since the original mortgage (late payments, defaults, CCJs) can result in refusal
Common reasons ports are refused: income reduction (especially for the self-employed during a bad trading year), new debts taken since original application, property type of the new home (lenders will not port to non-standard construction or properties above commercial premises), and the new loan-to-value exceeding the lender's maximum.
What Happens If You Need to Borrow More?
If your new property costs more than the remaining mortgage balance, you need a top-up. This additional amount is a new mortgage product at current rates — it does not port. You will have two mortgage components:
- Ported portion — at your existing rate for the remaining fixed term
- Top-up portion — at the current rate for a new fixed or tracker term
The terms on the top-up portion may not align with the end date of your existing deal. This creates a split mortgage where one portion reverts to SVR before the other. Most lenders allow you to choose terms that align, but check this explicitly.
What Happens If Your New Property Is Worth Less?
If you are downsizing to a cheaper property, you may need to repay part of your mortgage at redemption. This partial redemption during a fixed rate period may trigger an ERC on the amount you are repaying early — not the full balance. Check your mortgage offer document for how partial redemptions are treated. Some lenders allow partial redemptions of up to 10% per year without ERC.
The Simultaneous Exchange Problem
The biggest practical risk with porting is timing. Your sale and purchase must exchange and complete simultaneously — or within a very tight window — or the port fails. If your sale falls through after your purchase has exchanged, you face an ERC on redemption of the ported mortgage. This is a particular risk in a chain where other parties' timings are outside your control. Discuss the sequence risk explicitly with your solicitor before exchanging on a purchase if your sale is not yet exchanged.
When Porting Is Worth It
Porting makes financial sense when:
- Your existing rate is significantly below current market rates — if you fixed at 2% and current rates are 5%, porting saves you 3% on the ported balance
- You have a significant ERC remaining — if 3 years of a 5-year fix remain with a 3% ERC, porting avoids a potentially large charge
- Your new property qualifies and your affordability still passes — the application is more straightforward
Porting is less worthwhile when your existing rate is close to current market rates, when the administrative complexity creates timing risk, or when the top-up required is very large relative to the ported amount (meaning most of your mortgage is at current rates anyway).
The Alternative: Remortgage and Pay the ERC
In some cases it is cheaper to pay the ERC, remortgage freely with any lender, and take the best available deal on the full new mortgage amount. Model both scenarios:
- Cost of porting: £0 ERC + complexity + risk of refusal
- Cost of paying ERC: ERC amount (e.g. £5,000) + better rate on full balance for full term
If the rate saving over the remaining fixed period exceeds the ERC, porting wins. A mortgage broker can model both scenarios for your specific numbers.
This article is for information only and does not constitute financial or legal advice. Consult a qualified adviser for guidance tailored to your situation. Check the FCA register at register.fca.org.uk before dealing with any financial firm.
Frequently Asked Questions
What is a porting window and how long do I have?
Most lenders give you 3-6 months from redemption of your old mortgage to completing on the new purchase to qualify for port treatment. If completion on the new property takes longer, you lose the port and the ERC applies. Some lenders extend the window on request — ask your lender in writing before exchanging.
Can I port to a buy-to-let property?
Only if your mortgage was originally a buy-to-let. Residential mortgages cannot be ported to a buy-to-let property, and buy-to-let mortgages cannot be ported to a residential property. The FCA and most lender policies treat these as distinct products with different affordability rules.
Does porting affect my credit score?
The lender will perform a hard credit search as part of the re-affordability assessment. This is recorded on your credit file and may temporarily reduce your score. This is the same impact as any new mortgage application.
Can I port if I am in mortgage arrears?
Unlikely. A lender will not approve a porting application if you have recent or current arrears on the existing mortgage. Clear any arrears and allow time for the credit file record to be updated (30 days minimum) before applying to port.
What if my lender no longer operates or has been sold?
If your mortgage was sold to a different servicer (e.g. when a lender exits the market), the terms of your mortgage including portability provisions transfer with it. The new servicer must honour the original mortgage terms. Check the terms and contact them directly to confirm porting arrangements.
Sources
- FCA MCOB 11 Responsible Lending: handbook.fca.org.uk
- UK Finance Mortgage Lenders Handbook: ukfinance.org.uk
- MoneyHelper Remortgaging Guide: moneyhelper.org.uk
