Porting Your Mortgage: What It Actually Involves

Porting a mortgage is one of those financial concepts that sounds straightforward in principle but unravels into complexity the moment you try to execute it.

The basic premise is simple enough: you have a fixed-rate or tracker mortgage with a lender, you want to move house, and you'd rather not pay the early repayment charge (ERC) to exit your current deal.

So you "port" the mortgage—transferring it to a new property whilst keeping the same terms.

In practice, this involves a full mortgage application, a fresh affordability assessment, legal work, and a timing jigsaw that can fall apart at any stage.

This guide explains what actually happens when you port, what it costs, when it's worth doing, and where people go wrong.

What Porting Actually Means

Porting is not a simple administrative transfer.

It is a new mortgage application with your existing lender, subject to their current criteria, underwriting standards, and affordability calculations.

The only real difference between porting and a fresh remortgage is that—if approved—you keep your existing interest rate and product terms rather than moving to whatever deals are currently available on the market.

This matters because ERCs on fixed-rate mortgages typically range from 1% to 5% of the outstanding balance, which on a £300,000 mortgage could mean £3,000 to £15,000 in penalties if you redeem early.

Porting lets you avoid that charge, but only if your lender agrees to the transfer and you meet their requirements.

The critical point that many borrowers miss is that porting is discretionary.

Your lender has no obligation to approve the transfer.

If your circumstances have changed—your income has dropped, you've taken on new debts, your employment status has shifted, or the new property doesn't meet their lending criteria—they can refuse.

At that point, you're stuck: you either complete the house move and pay the ERC to redeem the mortgage, or you don't move at all.

There is no middle ground where you can force the lender to honour the original deal.

When Porting Makes Financial Sense

The decision to port hinges on a simple calculation: is the ERC you'd pay to exit greater than the additional interest you'd pay on a new deal at current rates?

If your existing mortgage is at 2.5% and current rates are 5.5%, porting saves you significant money over the remaining term—provided you can actually complete the transfer.

Conversely, if your existing rate is higher than what's currently available, paying the ERC and remortgaging might be cheaper overall.

The calculation becomes more complex when you need to borrow additional funds.

Most people moving house need a larger mortgage, not a straight transfer.

This is called "porting with additional borrowing" or a "product transfer with further advance." Your lender will typically offer you their current product rates for the additional amount, whilst the existing balance stays on the original rate.

This creates a blended rate across two products, and you need to calculate whether the overall cost is still competitive against remortgaging the whole amount to a new lender.

The Porting Process: Step by Step

Porting involves multiple stages, each with potential failure points.

Understanding the sequence helps you identify where delays are likely and what documents you'll need at each stage.

Stage 1: Initial Eligibility Check

Contact your lender as soon as you're considering a move—ideally before you put your property on the market or make an offer on a new one.

Ask specifically: "Is my product portable?" Not all mortgages are.

Some lenders, particularly smaller building societies and specialist lenders, offer products with no porting rights at all.

Others have restrictions on porting to certain property types (e.g., new-builds, flats above commercial premises) or in certain postcodes.

Get this confirmation in writing.

At this stage, also ask about the maximum loan-to-value (LTV) your lender will accept for ported mortgages.

If your existing mortgage is at 75% LTV but the new property would push you to 85% LTV, your lender may refuse the port or require you to pay down the balance.

Most lenders cap ported mortgages at 85% or 90% LTV, regardless of the original LTV.

Stage 2: Affordability Assessment

Once you have a property in mind and an agreed sale on your current home, you'll need to submit a full mortgage application.

Your lender will conduct a fresh affordability assessment based on your current circumstances, not those when you originally applied.

This includes:

Income verification: If you're employed, you'll need the last 3 months' payslips and P60.

Self-employed borrowers need 2-3 years of accounts or SA302 tax calculations from HMRC.

If your income has dropped since you took out the original mortgage—perhaps you've reduced hours, changed jobs, or your business profits have declined—this is where problems emerge.

Lenders apply current affordability stress tests, typically checking whether you can afford repayments at a rate 3% higher than your actual rate.

Expenditure analysis: Lenders now scrutinise bank statements more thoroughly than ever.

Regular gambling transactions, buy-now-pay-later usage, childcare costs, and maintenance payments all affect the calculation.

If your committed expenditure has increased since your original application—perhaps you've had children, taken on a car finance agreement, or are paying school fees—your borrowing capacity will be reduced.

Credit check: Your lender will run a hard credit search.

If your credit score has deteriorated—missed payments, increased credit utilisation, new defaults, or even just multiple credit applications—this can derail the port.

The lender's criteria may have also tightened since you originally applied.

What was acceptable in 2020 might not pass in 2024.

Stage 3: Valuation and Underwriting

Your lender will instruct a valuation on the new property.

This is not a survey; it's a check to ensure the property provides adequate security for the loan.

If the valuation comes in lower than the purchase price, you'll need to make up the difference with cash or the mortgage will be declined.

This is a common issue in fast-moving markets where buyers offer over asking price to secure properties.

The underwriting stage is where the decision is made.

Underwriters review the full application: your income and expenditure, the property valuation, your credit file, and your overall risk profile.

They may request additional documentation—bank statements covering a longer period, explanations for specific transactions, evidence of deposit source.

This stage can take anywhere from 2 days to 4 weeks depending on the lender and the complexity of your application.

Stage 4: Offer and Legal Work

If approved, you'll receive a mortgage offer.

This is a formal document setting out the terms of the loan.

The offer is typically valid for 3-6 months, so you need to complete within that window.

Your solicitor will then handle the legal work: transferring the title, registering the charge, and managing the funds.

If you're porting with additional borrowing, there may be two separate legal charges or a single consolidated one, depending on the lender.

Costs Involved in Porting

Porting is not free.

Whilst you avoid the ERC, you'll still incur various fees that can add up to £2,000-£5,000 or more depending on the transaction complexity.

Valuation fee: Lenders charge for the valuation on the new property.

This typically ranges from £200 for properties under £250,000 to £600+ for properties over £500,000.

Some lenders waive this fee for existing customers porting, but many don't.

Ask upfront.

Product fee: If you're taking additional borrowing, you'll pay a product fee on that portion.

These range from £0 to £1,999 depending on the deal.

Some lenders charge a separate product fee for the port itself, even without additional borrowing—typically £500-£1,000.

Legal fees: You'll need a solicitor for the purchase.

If you're porting with the same lender, you may be able to use their panel solicitor at a reduced rate, typically £800-£1,500 for a freehold property.

However, these panel firms can be slow and overworked.

Using an independent solicitor costs more (£1,200-£2,000+) but may provide better service.

Broker fee: If you use a mortgage broker to arrange the port, they may charge a fee of £300-£500.

This can be worth it if your situation is complex or if you're comparing the port against remortgaging options.

Higher lending charge: If your new LTV exceeds 75% or 80%, some lenders charge a higher lending charge or require mortgage indemnity insurance.

This can be 1-2% of the loan amount and is typically added to the mortgage balance.

Common Reasons Ports Get Declined

Understanding why ports fail helps you assess your own risk before committing to a house move.

The most common decline reasons include:

Affordability failure: Your income has changed, your expenses have increased, or the lender's affordability calculations have tightened.

This is the single biggest reason ports are declined.

If you've taken on any new credit since your original mortgage—car finance, credit cards, loans—this reduces your borrowing capacity.

Childcare costs are now scrutinised heavily; if you've had children since taking out the mortgage, the affordability calculation will reflect this ongoing commitment.

Property issues: The new property doesn't meet the lender's criteria.

This includes non-standard construction (timber frame, concrete, steel frame), flats above commercial premises, properties with flying freeholds, listed buildings requiring specific maintenance, new-builds (many lenders restrict LTV on new-builds), and properties in areas of flood risk or structural concern.

If the valuation identifies issues—cladding problems in flats, Japanese knotweed nearby, subsidence history—the lender may decline regardless of your personal finances.

Credit deterioration: Your credit file shows missed payments, defaults, or increased credit utilisation since the original mortgage was taken out.

Even small issues—a missed credit card payment, a default on a mobile phone contract—can cause automatic declines with some lenders.

Check your credit file with all three UK agencies (Experian, Equifax, TransUnion) before applying to port.

Employment changes: You've changed jobs, become self-employed, or your employment type has shifted.

Lenders typically want to see 3-6 months in a new job before accepting an application, and self-employed borrowers need 2-3 years of accounts.

If you've moved from employed to self-employed since taking out the mortgage, this is a significant red flag.

"The number of borrowers who assume porting is guaranteed because they've never missed a payment is staggering.

Affordability is recalculated from scratch, and the criteria that applied five years ago don't apply today.

We see people stuck in chains because they didn't check porting eligibility before listing their home." — Senior Mortgage Underwriter, UK High Street Bank

Timing and Chain Considerations

Porting adds complexity to an already complex process.

The typical timeline from application to offer is 2-6 weeks, but this can extend significantly if there are queries or if your circumstances are unusual.

You need to factor this into your chain negotiations.

The ERC refund window is critical.

Most lenders operate a system where you have 3-6 months between redeeming your existing mortgage and completing the port to claim back the ERC.

This means you can sell your current property, pay the ERC, then reclaim it when you complete on the new property.

However, if the purchase falls through after you've sold, you lose the ERC permanently.

Some lenders offer longer windows—up to 12 months—but this varies.

Check your mortgage terms or call your lender to confirm the exact period.

If you're in a chain, delays anywhere in that chain can push you beyond the ERC refund window.

If you're selling to a first-time buyer whose mortgage offer expires, or buying from someone whose purchase falls through, your timeline can extend unpredictably.

Build contingency into your planning and communicate the ERC deadline to your solicitor and estate agent.

Porting vs Remortgaging: A Decision Framework

Not every situation calls for porting.

Sometimes paying the ERC and remortgaging to a new lender is the better financial decision.

Use this framework to decide:

Port when: Your existing rate is significantly below current market rates (more than 1% difference), you have several years left on your fixed term, the ERC is substantial (over £5,000), your circumstances haven't deteriorated since the original application, and the new property meets your lender's criteria without issue.

Remortgage when: Your existing rate is at or above current market rates, you have less than 2 years left on your fixed term, the ERC is relatively small, you want to borrow significantly more (which might be cheaper with a new lender), your circumstances have improved (higher income, lower debts) and you might get better terms elsewhere, or you want to switch lenders for service reasons.

Compare both: When rates are similar, the decision hinges on fees, flexibility, and your future plans.

A new lender might offer a fee-free deal with better overpayment flexibility.

Your existing lender might offer a product switch on the additional borrowing that's competitive.

Run the numbers for both scenarios.

Checklist Before You Commit

Before you put your house on the market or make an offer on a new property, work through this checklist:

✅ Confirm in writing that your mortgage product is portable
✅ Check the ERC refund window (typically 3-6 months)
✅ Obtain your current mortgage balance and LTV
✅ Check your credit file with all three UK agencies
✅ Calculate whether porting or remortgaging is cheaper over the remaining term
✅ Gather income evidence (payslips, P60, accounts if self-employed)
✅ Document any changes in circumstances since original application
✅ Ask your lender for a porting illustration showing costs and terms
✅ Confirm the maximum LTV your lender will accept for a ported mortgage
✅ Check if your lender has any property type restrictions
❌ Don't assume porting is guaranteed because you've never missed a payment
❌ Don't commit to a house purchase before getting a mortgage offer in principle
❌ Don't take on new credit before the port completes
❌ Don't change jobs during the application process
❌ Don't assume the ERC refund window is unlimited

Special Situations

Porting with Bad Credit

If your credit has deteriorated since taking out the mortgage, porting becomes significantly harder.

Your existing lender may decline the application, leaving you with the choice of paying the ERC or not moving.

Some specialist lenders consider porting for customers with adverse credit, but this is assessed case-by-case.

If you have missed payments, defaults, or CCJs, speak to a whole-of-market broker before listing your property.

They can assess whether any lender would accept a port or remortgage given your circumstances.

Porting After Divorce or Separation

If you're porting a joint mortgage to a property in your sole name, or transferring to a new joint owner