Changing Your Mortgage to Buy-to-Let: Consent to Let or Full Switch
Updated 23 September 2026
You can change a residential mortgage to a buy-to-let, and there are three ways to do it: ask your current lender for consent to let and keep the existing deal, switch the loan onto a buy-to-let product, or run a let-to-buy where the old home is remortgaged as a rental and a new residential mortgage funds the next one. Which route fits depends on how long you will let the property, how much equity it holds and whether the rent covers the lender’s stress test. Mortgage One is a whole of market mortgage adviser arranging consent to let, buy-to-let switches and let-to-buy mortgages for homeowners becoming landlords.
If you are moving in the next few months and want to keep your current home as a rental rather than sell it, call 01202 155992 or contact Mortgage One.
Can you change a residential mortgage to a buy-to-let?
Yes. A residential mortgage can be changed to a buy-to-let either by the current lender granting consent to let, which keeps the existing deal in place for a limited period, or by remortgaging onto a buy-to-let product with the same or a different lender. Letting without either breaches the mortgage conditions and lets the lender call in the loan.
The distinction matters because residential and buy-to-let lending are assessed on different things. A residential mortgage is underwritten on your income and outgoings. A buy-to-let mortgage is underwritten mainly on the rent the property will earn, tested against a stressed interest rate, with your personal income as a secondary check. Moving from one to the other therefore means the property has to qualify as an investment, not just you as a borrower.
Timing usually decides the route. A posting abroad for a year, a trial move in with a partner or a home that will not sell at the right price points to consent to let. A permanent decision to keep the property as an investment points to a full buy-to-let switch, because consent is temporary and lenders expect the loan to be moved onto the right product once the letting is settled. Our buy-to-let mortgage guide covers how lenders read a first rental property from the landlord’s side.
Consent to let: renting out your home on your current mortgage
Consent to let is your lender’s written permission to rent out the property while keeping the residential mortgage. Halifax grants it for 12 months at a time with a 0.5% rate uplift and no fee, Nationwide adds 0.5% while the property is let, NatWest charges £120 at outset and £120 a year, and Santander £295 per request.
The terms above are each lender’s published position as at 22 September 2026, and they show the shape of the market rather than a universal rule. Most lenders require the mortgage to have run for at least six months before they will consider consent, Halifax being one that says so explicitly, and most limit the arrangement to a single tenancy under an assured tenancy agreement rather than a house share or short lets. Consent is granted for a period, commonly a year with review, and the lender expects you either to move back in or to remortgage onto a buy-to-let product at the end of it.
The appeal is that nothing else changes: same deal, same early repayment charge schedule, no valuation, no new application. The catch is that a residential fixed rate carrying a 0.5% loading is often more expensive than a purpose-built buy-to-let deal once the letting runs beyond a year or two, and the tax position on the rental income starts on day one regardless of which mortgage sits behind it.
Switching to a full buy-to-let mortgage: what lenders check
A full switch to a buy-to-let mortgage is assessed on the rent. Lenders typically want the property at no more than 75% loan-to-value, and rent that covers the mortgage interest by 125% for a basic-rate taxpayer or 145% for a higher-rate taxpayer, calculated at a stressed rate of around 5.5% rather than the rate you will actually pay.
The 5.5% figure comes from the Prudential Regulation Authority’s expectations for buy-to-let underwriting, which set a minimum 125% interest coverage ratio and an interest rate stress test of at least 5.5% on most cases, with lenders free to apply stricter versions. On a £200,000 loan at a 5.5% stress rate the monthly interest is £917, so a basic-rate taxpayer needs rent of about £1,146 a month and a higher-rate taxpayer about £1,329. Our buy-to-let rental stress test calculator runs the same buy-to-let stress test on your own figures, and it is the first check to make before assuming the switch will work.
Loan-to-value is the second gate. If you bought with a 10% deposit and the property has not risen much in value, the equity may sit well below the 25% most buy-to-let lenders want, and the switch stalls until the balance is reduced or the value rises. The remaining checks mirror a purchase: personal income, often with a minimum threshold, credit history, the property type, and whether you already own a home you live in, which most lenders prefer. If the switch is within the fixed period of the residential deal, the early repayment charge applies to the remortgage in the same way as any other, unless the existing lender will move you onto its own buy-to-let range without one.
How does a let-to-buy mortgage work when you buy your next home?
A let-to-buy arrangement remortgages your current home onto a buy-to-let loan, typically at up to 75% loan-to-value, and releases equity towards the deposit on a new residential purchase, which runs as a standard home mover mortgage. Both loans complete on the same day, and the residential lender assesses your income with the buy-to-let mortgage running in the background.
The two mortgages are underwritten separately but have to be arranged together. The buy-to-let side is sized on the rent the current home will achieve, using the coverage sums above, and the amount it can release is capped by the loan-to-value limit. The residential side is sized on your income, with the new rental treated as self-financing where the rent covers the interest, and some lenders wanting to see a letting agent’s rental assessment before they ignore the background loan. Getting the two offers to land in the same week, with the same completion date, is the part of a let-to-buy that most often goes wrong when the mortgages are arranged with two lenders that have not been told about each other.
Stamp duty is the cost people miss. Because you will own two properties on completion, the purchase of the new home in England and Northern Ireland attracts the additional-property surcharge of 5 percentage points on top of the standard rates, which has applied since 31 October 2024. If you later sell the original home within 36 months, the surcharge can be reclaimed on the basis that you replaced your main residence. Our stamp duty calculator sizes the surcharge against the purchase price, and the second home mortgage guide covers the case where the second property is for your own use rather than tenants.
For a free initial consultation that sizes both halves of a let-to-buy, the rent cover on your current home and the borrowing on the next one, call 01202 155992 or contact Mortgage One.
Remortgaging to buy another property with released equity
You can remortgage your home to release equity for a deposit on another property, whether a buy-to-let, a second home or a let-to-buy purchase. Residential lenders commonly allow capital raising up to 80% or 85% loan-to-value, a small number go to 90%, and the new borrowing has to pass affordability alongside any mortgage on the property being bought.
The order of operations is what separates a smooth purchase from a stalled one. The equity release completes first or on the same day as the purchase, so the deposit is evidenced as cleared funds when the purchase lender asks for it. Where the property being bought is a buy-to-let, the purchase lender will want a 25% deposit and rent that passes its own stress test, and it will count the enlarged residential mortgage in your outgoings. Where the new property is a home you will live in, the roles reverse and the current home becomes the rental, which is the let-to-buy case above.
A further advance from the existing lender is the alternative to a full remortgage when the current deal is competitive and mid-term, because it avoids the early repayment charge at the cost of a second sub-account on a higher rate. Our remortgage advice guide weighs the two routes on total cost, and landlords growing beyond a single property should read the portfolio landlord rules before the fourth mortgaged rental, because underwriting changes at that point.
Can you change a buy-to-let mortgage back to residential?
Yes, but only by applying for a new residential mortgage, because a standard buy-to-let loan is unregulated and its terms prohibit the borrower living in the property. The lender assesses the residential application on your income and affordability from scratch, and the early repayment charge on the buy-to-let deal applies if it is still within its fixed period.
Moving back into a rental without changing the mortgage is the mirror image of letting without consent: it breaches the conditions and can allow the lender to demand repayment. Some lenders will convert their own buy-to-let customers onto a residential product, others require a full remortgage elsewhere, and either way the case is underwritten as if you were buying the property for the first time, with the current balance treated as the loan requested. Where a family member rather than you will live in the property, a regulated buy-to-let is the product lenders use, and it is assessed on affordability rather than purely on rent.
The tenancy also has to end lawfully before you move in. Under the Renters’ Rights Act 2025, in force for the main tenancy reforms since 1 May 2026, tenancies are periodic and the landlord needs a valid ground to regain possession, so the mortgage timetable has to follow the possession timetable rather than lead it.
Tax, the Renters’ Rights Act and what changes once you are a landlord
Once your home is let, rental income is taxable and mortgage interest is no longer deductible in full. Since 6 April 2020 individual landlords receive a basic-rate tax credit of 20% on finance costs instead, which is why higher-rate taxpayers often see a bigger tax bill than the cash surplus suggests, and why many use a limited company later.
The tax credit rule, known as Section 24, is the reason the 145% rent cover figure exists for higher-rate taxpayers: lenders stress the case harder because the tax leaves less of the rent behind. It does not usually make sense to move an existing home into a company, because the transfer is a sale for stamp duty and capital gains purposes, but it is the reason many landlords buy their second and later properties through one. Our limited company buy-to-let guide sets out how lenders assess that structure. Tax treatment depends on individual circumstances and can change, so an accountant should confirm the position before the letting starts.
The letting itself is regulated more tightly than it was. The Renters’ Rights Act 2025 abolished section 21 evictions and assured shorthold tenancies from 1 May 2026, so every new tenancy is periodic from the outset and possession depends on a statutory ground. For an accidental landlord that changes the calculation on consent to let, because getting the property back at the end of a twelve-month consent period is no longer a matter of serving notice and waiting. If the plan is short lets to guests rather than a tenancy, a different product applies, and our holiday let mortgage guide explains why lenders treat that as a separate case.
To have consent to let, a full buy-to-let switch and a let-to-buy costed against your own rent, equity and moving date, call 01202 155992 or contact Mortgage One.
The information provided in this article is for general guidance only and does not constitute personal or regulated financial advice. If you’d like to understand what these moves could mean for you, speak to Mortgage One. We can explain your options and timings based on your specific circumstances.
FAQs
1. How much does it cost to convert a mortgage to buy-to-let?
Consent to let is the cheaper route, with published costs ranging from no fee and a 0.5% rate uplift at Halifax to a £295 fee per request at Santander. A full switch to a buy-to-let product carries the usual remortgage costs, a product fee, valuation and legal work, plus any early repayment charge if the residential fix has not ended.
2. What are the downsides of a buy-to-let mortgage?
The rate and fees are usually higher than on a residential deal, the deposit or equity requirement is 25% with most lenders, the loan is sized on rent rather than income, and most buy-to-let mortgages are interest-only, so the balance does not fall unless you overpay. Void periods and repairs come out of the rent before the mortgage does.
3. Is it still worth being a landlord in 2026?
It depends on the yield, the tax position and how long you hold the property. Mortgage interest relief is limited to a 20% tax credit for individuals, the Renters’ Rights Act has removed section 21, and stamp duty on additional properties carries a 5 percentage point surcharge. Against that, rent cover requirements mean a property that passes the lender’s test is usually cash-positive from the start.
4. What is the six month rule for mortgages?
A convention among most mainstream lenders not to remortgage a property until six months after the purchase or last remortgage was registered at HM Land Registry. It affects a let-to-buy or a buy-to-let switch on a recently bought home, because the buy-to-let remortgage may have to wait, although some specialist lenders will consider a case inside six months.
5. Do you need a buy-to-let mortgage for Airbnb?
Not a standard buy-to-let mortgage, because that product assumes a tenancy rather than short lets to guests. Letting a home on Airbnb needs either the lender’s specific consent or a holiday let mortgage, which is assessed on projected seasonal income and usually requires a larger deposit than a buy-to-let.
6. Can a broker arrange the buy-to-let switch and the new purchase together?
Yes, and on a let-to-buy that is the point of using one. A whole of market broker places the buy-to-let remortgage and the residential purchase with lenders that accept each other’s loan in the background, aligns the two offers and completion dates, and checks the rent cover and stamp duty position before you commit to the purchase.