Porting lets you carry your existing mortgage rate and terms to a new property instead of paying an early repayment charge and starting fresh. This guide covers what porting genuinely is beneath the reassuring name, why it can still be refused even on a fully portable product, and how the maths works when you need to borrow more to fund the move.
Figures below reflect published 2026 mortgage broker guidance and major UK lender porting policies, current to mid-2026. This is general information, not financial advice; confirm your specific mortgage's portability and current terms directly with your lender or a broker.
1. The misconception the name creates
Porting means taking your existing mortgage rate, lender, and terms with you when you move, but the mechanism is genuinely a fresh mortgage application, not a simple transfer of the old one. You must requalify under today's affordability rules, and the lender must separately approve the new property as security, exactly as if you were applying from scratch. The rate and product are what's inherited from the old deal; the underwriting, the approval, and the legal agreement itself are entirely new.
2. How porting actually works, mechanically
- You apply to port at the same time as exchanging on the new property, notifying your existing lender of the move.
- The lender reassesses your income, outgoings, and the new property, typically requiring a fresh valuation.
- Your existing mortgage is technically redeemed (paid off in full) on completion of the sale of your current home.
- A new mortgage is issued on completion of the purchase of your new home, usually on the very same day, carrying forward your old rate and remaining term.
Because the redemption and the new lending happen simultaneously, the lender treats it as a continuous arrangement rather than an early exit, which is precisely why no early repayment charge applies to the portion you carry across.
3. Why porting gets refused even on a portable mortgage
Even where your mortgage offer document confirms your product is portable, porting is refused in a meaningful number of cases. Common reasons include: failing the lender's updated affordability assessment, particularly following a change in income, employment, or personal circumstances since the original application; the new property not meeting the lender's current lending criteria, for example non-standard construction or a leasehold with a short remaining lease; and an inability to complete a simultaneous exchange if you need to exchange on the new property before completing the sale of your current one, which some lenders won't accommodate.
4. Borrowing more: the two-rate blend
If the new property costs more than your existing mortgage balance, you'll typically need additional borrowing, usually offered as a separate top-up loan alongside the ported portion. The ported balance keeps your existing rate; the top-up is priced at the lender's current product rate, which may be considerably higher if rates have moved since you first fixed. The practical result is a single mortgage made up of two parts on two different rates, blended into one monthly payment, and it's worth working out that blended figure properly rather than assuming the whole loan sits at your old, cheaper rate.
5. The genuine early repayment charge saving
The core financial case for porting is avoiding an early repayment charge that would otherwise apply to breaking your current deal early. As an illustrative example, someone two years into a five-year fix, with an ERC of 3% to 4% of the outstanding balance, could face a charge of roughly £6,000 to £8,000 on a £200,000 mortgage if they remortgaged elsewhere instead. Porting protects your existing rate specifically where that rate beats what's currently available in the market; if rates have fallen since you fixed, a fresh remortgage to a new lender may make more financial sense than porting an outdated, now-uncompetitive rate.
6. The timing problem: buying and selling simultaneously
Porting works most smoothly when the sale of your current home and the purchase of your new one complete on the same day, since that's what allows the redemption and reissue to happen back to back without a gap. If your timeline doesn't align this neatly, some lenders can accommodate a short gap through a second mortgage or bridging arrangement, but this genuinely adds complexity and cost, and not every lender offers it. Confirming your specific lender's approach to timing mismatches before relying on porting as your plan is worth doing early, rather than discovering the limitation partway through a chain.
7. Frequently asked questions
Is porting a mortgage automatic if my product allows it?
No. Even if your mortgage offer confirms your product is portable, porting still requires a fresh affordability assessment and the lender's acceptance of the new property. A meaningful number of attempted ports are refused because circumstances have changed since the original application, or the new property doesn't meet the lender's current criteria.
What happens if the new property costs more than my current mortgage balance?
You'll typically need additional borrowing, offered as a separate top-up loan alongside your ported mortgage. The ported portion keeps your existing rate, while the top-up is priced at the lender's current product rate, which may be considerably higher. The result is a mortgage with two parts on two different rates, blended into a single monthly payment.
Can porting fail even on a construction or leasehold basis?
Yes. Porting can be refused if the new property doesn't meet the lender's lending criteria, including non-standard construction types or a leasehold property with a short remaining lease, even where your existing mortgage and financial circumstances are otherwise unchanged.
How much does porting typically save compared with paying an early repayment charge?
It depends on how far into your current fixed deal you are and the size of your mortgage. As an illustrative example, someone two years into a five-year fix with an ERC of 3% to 4% on a £200,000 balance could face an early repayment charge of roughly £6,000 to £8,000 if they remortgaged elsewhere instead of porting.
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