Let-to-Buy: What Keeping Your Old Home Really Costs
Buy-to-Let · 7 minute read
Let-to-Buy: What Keeping Your Old Home Really Costs
By Kieran Ali, founder of CiK Finance · Published 3 August 2026
Key takeaways
- Let-to-buy means remortgaging the home you live in onto buy-to-let terms and buying your next home at the same time. The two transactions run together.
- Because you end up owning two properties, the 5% additional-dwellings stamp duty surcharge applies to the new purchase. On a £600,000 home that is £50,000 instead of £20,000.
- Most lenders want you to have owned and lived in the property for at least six months, with a simultaneous onward purchase and the same solicitor acting on both sides.
- Maximum borrowing on the property you are letting commonly sits around 80% of its value, so the equity has to already be there.
- If the rent falls short of the lender's stress test, top slicing can, in certain cases, bridge the gap using your earned income.
- Consent to let is a different thing entirely, and choosing it by accident can strand the deposit you needed.
"Can I rent out my house and buy another one?"
Ten versions of that question have crossed my desk in the last two months. Some from people moving abroad for work, some from people buying their first investment property almost by accident, all of them looking at a house they already own and wondering whether letting go of it is really necessary.
Usually the answer is that you can. The more useful question, and the one this article is actually about, is what it costs you and whether it is the right move at all.
What let-to-buy actually is
Let-to-buy is two transactions happening at once.
You remortgage your current home onto buy-to-let terms, which usually releases some equity as capital. That capital very often becomes the deposit on the next property. At the same time you buy the new home you are going to live in, on an ordinary residential mortgage.
The old house stays yours with a tenant in it. The new house becomes your main residence. One set of paperwork, two completions, and they have to happen on the same day.
People sometimes describe this as "turning my house into a buy-to-let", which is close enough. What it is not is the same as asking your existing lender for permission to rent the place out. That is consent to let, and I will come back to why the difference matters more than it sounds.
The stamp duty bill nobody budgets for
This is the part that catches people, and it catches them late.
Stamp duty has a higher rate for what HMRC calls additional dwellings. If, at the end of the day you complete, you own two or more residential properties and you have not replaced your main residence, you pay the standard rates plus five percentage points. That surcharge has been 5% since 31 October 2024.
Keeping your old home is exactly that situation. You have not replaced anything. You have added.
Here is what it looks like on a £600,000 purchase, using the residential rates published on GOV.UK:
- Sell the old house, buy at standard rates: £20,000
- Keep the old house, buy at the higher rates: £50,000
Thirty thousand pounds, for the decision to hold onto a property you already own. It is not a penalty for doing something wrong; it is just how the rules work. But it needs to be in the sum from the beginning, because it comes out of the same pot as your deposit.
Two things make it worse if they apply to you. The nil rate band dropped back to £125,000 on 1 April 2025, so there is less shelter at the bottom than there was. And if you are not UK resident for stamp duty purposes, a further 2% goes on top, taking the combined surcharge to 7%.
I am not a tax adviser and none of this is tax advice. Your solicitor or accountant needs to confirm your position before you commit, particularly around the rules on replacing a main residence, which have more nuance than a blog post can carry.
What lenders want to see
Let-to-buy has its own criteria and they are stricter than a standard remortgage. The common shapes, drawn from published intermediary criteria at lenders including The Mortgage Works and Family Building Society:
- You have owned and lived in the property for at least six months at the point you apply.
- There is a simultaneous onward purchase. Lenders want the new address on the application, and if you are buying with a mortgage they will want to see that offer before completion.
- Maximum borrowing on the property you are letting commonly runs to around 80% of its value.
- The same solicitor acts on both the remortgage and the purchase. This one is not negotiable and it does limit who you can instruct.
- The new property has to be immediately habitable, confirmed by the sales particulars or a valuation.
Criteria vary between lenders and change regularly, so treat those as the shape rather than the rule. Any lending is subject to underwriting.
The practical point is the timing. Two transactions completing on the same day, one solicitor holding both, and no slack in the chain if something runs late. Getting the solicitor instructed early matters more here than on an ordinary purchase.
When the rent does not stretch far enough
Buy-to-let borrowing is decided mostly by the rent, not by what you earn.
The rental income has to cover the mortgage payment by a set margin, tested at a rate higher than the one you would actually pay. If it falls short, the loan gets capped at whatever the rent supports. Someone on a very comfortable salary can find their borrowing limited by a rent that is ninety pounds a month lighter than the calculation wanted.
Top slicing is the answer to that specific problem. Some lenders can, in certain cases, take surplus earned income into account to bridge the gap between what the rent supports and what you need. Not every lender offers it, those that do set their own minimum income requirements, and some restrict it by applicant type.
It is worth being clear about what it is not. Top slicing does not let you borrow more than you can afford. The income has to be there and it has to be evidenced. It is a different way of reading the same file.
A recent case of ours ran on exactly this. A client working overseas needed £750,000 against a UK property he already owned, raising capital in the process. The rent covered a good part of that but not all of it, and on the standard calculation the conversation would have stopped there. Being paid abroad narrowed the panel again before anyone had looked at the numbers properly. A specialist lender able to top slice took his earned income into account, and the case completed at the figure he needed.
The lesson is not that top slicing rescues everything. It is that a capped figure is a criteria answer from one lender, not a fact about your situation.
Consent to let is not the same thing
Consent to let is permission from your current lender to rent the property out while you stay on your existing residential mortgage. It is usually temporary, it often carries a fee or a rate change, and it releases no equity at all.
That last part is what causes the damage. People ring their bank, get consent to let, feel organised, and only later work out that the deposit they needed for the next house was sitting inside the property they have just agreed not to remortgage.
Consent to let genuinely suits some situations. An eighteen month posting abroad with every intention of moving back in is a good example. If you need the equity, or you are letting the property indefinitely, let-to-buy is usually the structure that fits.
Both are legitimate. They solve different problems, and the right one depends on how long you are letting it and whether you need the money out.
When keeping it is the wrong call
I have written a lot here about how to do this. It is worth saying plainly that a fair number of people should not.
Keeping your old home is emotionally easy. You already own it, you know its quirks, and selling can feel like going backwards. None of that is a financial reason, and all of it does a lot of quiet work in the decision.
The cases where it does not stack up follow a pattern. The equity you leave in the old property is the deposit that would have bought you a better next house. The stamp duty surcharge costs more than the first two or three years of rental profit. The property is somewhere you chose for the schools and the commute, and you would never pick it as an investment. Or the honest version: the numbers only work if the tenant pays every month for the next decade without a gap.
Of the ten cases I mentioned at the start, two decided to sell. I think both were right.
The question to answer before any of this
What I like to do is work backwards, and it takes longer than people expect.
What do you want this property to do? Income now, growth over twenty years, somewhere a child might live, a pension you can see. These pull in different directions and the first answer is rarely the honest one.
Do you need the money coming in now, or when you stop working? A property built to pay you today is often the wrong one to still be holding at sixty.
And how many do you want to own by the time you finish? One is a decision. Six is a plan, and it changes what you should do with this first one.
Here is the test I keep coming back to. If you had the cash equivalent of that equity sitting in your account today, would you go out and buy that specific house as an investment?
If the answer is no, keeping it deserves a much better reason than it seeming a shame to sell.
Common questions
Do I pay the stamp duty surcharge if I keep my old home?
Generally yes. If you own two or more residential properties at the end of the day you complete, and you have not replaced your main residence by selling the old one, the higher rates apply to the new purchase. That is standard rates plus five percentage points. The rules on replacing a main residence have exceptions, so confirm your position with your solicitor before you commit.
How long do I need to have lived in the property?
Most lenders want at least six months of ownership and occupation before they will consider a let-to-buy remortgage. Some ask for longer. It is one of the first things worth checking, because it can delay a plan by months.
Can I do let-to-buy if I am living abroad?
Often, yes, though the list of lenders is shorter and they will look at where your income comes from, what currency it is paid in, and what UK footprint you have kept. If you are not UK resident for stamp duty purposes there is also a further 2% surcharge on the purchase. It is a more specialist case rather than an impossible one.
What happens if the rent does not cover the mortgage?
The loan is normally capped at whatever the rent supports under the lender's stress test. Some lenders can, in certain cases, use top slicing to take your surplus earned income into account and bridge the shortfall. Minimum income requirements apply and not every lender offers it.
Is let-to-buy the same as buy-to-let?
No. Buy-to-let is buying a property specifically to rent out. Let-to-buy is converting the home you already live in to a rental while buying somewhere new to live. The lending is similar; the criteria and the transaction structure are not.
Weighing up whether to keep it?
We will run both versions before you commit to either: keeping the property and letting it, or selling and putting the equity into the next one. No obligation.
Kieran Ali is the founder of CiK Finance, a specialist mortgage and protection firm working with company directors, portfolio landlords and clients with complex income. CiK Financial Ltd is an appointed representative of PRIMIS Mortgage Network, a trading name of First Complete Limited, which is authorised and regulated by the Financial Conduct Authority.
Information correct at the time of publication (3 August 2026) and subject to change. Figures shown are illustrations only; any lending is subject to underwriting, and criteria can change depending on circumstances. Tax treatment depends on individual circumstances and may change; CiK Finance does not provide tax advice, so please speak to your solicitor, accountant or a qualified tax adviser.
Most Buy-to-Let Mortgages are not regulated by the Financial Conduct Authority.
Your home may be repossessed if you do not keep up repayments on your mortgage.