Let to Buy Explained
If you’re looking at a let to buy, the real question isn’t just “how much can I borrow?”
You are effectively trying to make two things work at once:
- your current home has to work as a buy-to-let
- your onward purchase has to work as a residential case
And those two decisions do not always line up neatly.
This calculator tests whether those two sides hold together, factoring in rental stress testing and residential affordability — showing where the case is likely to pass or break.
Looking to buy or remortgage a property purely to rent out? Use our buy-to-let calculator instead.
Before you run it
What to Know Before Using This Calculator
- A let to buy is assessed as two separate mortgages
- Rental income is stress tested, not just compared to the payment
- Your new residential borrowing depends on how lenders treat the existing property
- Different lenders can reach very different outcomes on the same case
- This tool produces a structured result, showing whether the case is likely to work, fall short, or sit in a borderline range, along with the key constraints shaping that outcome.
Let to buy calculator
Check whether the structure stacks up
Get a quick view of whether a let to buy could work based on your current property, rent, income, commitments, savings, and onward purchase.
Regular monthly payments that would still apply after moving. For example: loans, car finance, credit cards with set payments, school fees, childcare, maintenance, and other fixed committed costs. Do not include groceries, utilities, council tax, or your current mortgage payment.
Before you spend months building plans around a mortgage, understand where people usually get caught out.
Most people only realise how differently mortgage applications are interpreted once something slows down, falls apart, or stops making sense. This short walkthrough helps you recognise problems earlier, before you commit too much time, money or certainty to the wrong path.
See where borrowers get caught out →What This Let to Buy Calculator Is Really Testing
1. Can your current home support a buy-to-let mortgage?
This depends on the expected rent, the property value, and the way lenders stress test rental income.
2. Can you borrow enough for the onward residential purchase?
This depends on income, deposit, fixed commitments, and how the lender treats the fact you still own the existing property.
3. Do the two sides still work together once everything is added up?
This is where many let to buy cases become harder than they first appear.
How Lenders Assess a Let to Buy Mortgage
Let to Buy is a collision of lending criteria that becomes quite demanding on the overall structure.
The buy-to-let side (your current home)
Lenders want to know whether your current property works as a rental.
They usually look at:
- expected monthly rent
- property value
- existing mortgage balance
- loan-to-value
- rental stress testing
- whether the application is in a personal name or another structure
In practice, the rent is not simply compared to the mortgage payment. Lenders often apply a stressed interest rate and require the rent to cover a margin above that figure. This is why a property that feels “obviously rentable” can still fail a lender’s calculation.
The residential side (your new home)
Separately, lenders assess whether you can afford the new home.
They usually look at:
- salary and any other usable income
- fixed monthly commitments
- deposit size
- credit profile
- how the existing property is treated in the affordability model
This is where lender interpretation starts to matter more. Some lenders are comfortable once the rental side stands on its own. Others still apply tighter assumptions because you still own the original property.
If you want to understand why a case that looks fine here can still fail, see how let-to-buy is actually assessed.
Why Two Lenders Can Reach Different Answers on the Same Let to Buy Case
This is one of the biggest sources of confusion for borrowers.
Two cases can look almost identical on paper and still produce different outcomes because lenders do not all assess let to buy structures in the same way.
Some lenders may:
- ignore the existing mortgage if the rent covers it comfortably
- include part of it as a commitment
- require the let to buy and onward purchase to be done together
- restrict how much equity can be released
- apply tighter rules where income is variable or the deposit is being created from the existing property
In practice, I often see let to buy cases break down here. The problem is not always that the borrower cannot afford it. The problem is that the structure does not line up with the way a particular lender assesses risk.
Common Reasons Let to Buy Cases Fail
Most let to buy cases run into trouble for one of a few predictable reasons:
- the expected rent does not meet the lender’s stress test
- there is not enough usable equity in the current property
- releasing deposit funds weakens the buy-to-let side too much
- residential affordability becomes tight once commitments are factored in
- the lender’s policy on linked cases is stricter than expected
- the timings between moving, refinancing and buying do not line up
A lot of borrowers assume the key question is whether they can “afford both”. That matters, but the bigger issue is often whether the case is structured in a way a lender will actually accept.
When a Let to Buy Mortgage Becomes More Complex
Some cases naturally need more careful lender selection.
This usually happens where there is:
- high loan-to-value on the current home
- lower rental yield
- variable income or multiple income sources
- recent job change
- a short track record in the current role
- more than one existing property
- deposit money being created by releasing equity
These are the cases where the difference between lenders starts to matter far more than a basic online affordability estimate.
Let to Buy vs Buy to Let vs Consent to Let
Both these mortgage types are options if you are looking to rent out a property. A let to buy mortgage is applicable if you want to rent out a property you already own and currently live in.
A buy to let mortgage is applicable if you want to specifically buy a property to let out. The reality is that they are extremely similar but lenders will often review the situations differently, have different lending criteria and possibly different deals.
If you want to understand how buy-to-let works and why cases are assessed differently, see why buy-to-let deals get declined.
Let to buy
You keep your current home, switch it to a rental structure, and buy a new home to live in.
Buy to let
You buy a property specifically as an investment property to rent out.
Consent to Let
You keep your current residential mortgage and ask the lender for permission to let the property, usually on a temporary basis.
They can overlap in practice, but lenders do not always treat them the same way. A borrower comparing these options usually needs to understand not just the product difference, but how each route affects onward borrowing and lender appetite.
Important Things to Consider With Let to Buy
There are many responsibilities attached to being a landlord. Do your research and ensure you have carefully considered what will be involved.
Ensure you can afford the additional debt. Most importantly, you will need to be able to afford your monthly mortgage payments should your rental property be empty for several months of the year or if interest rates increase.
You cannot live in a property with a buy to let mortgage and, vice versa, you cannot rent out a property that has a residential mortgage on it without the lender’s consent.
In some cases, a bridging loan will be competitively priced and offer more flexibility if you are planning to sell.
What to Prepare Before Speaking to a Broker
To assess a let to buy case properly, it helps to have:
- an estimated rental figure for your current home
- current mortgage balance
- rough current property value
- income breakdown
- monthly fixed commitments
- expected deposit strategy
- rough purchase price for the onward home
The clearer those numbers are, the easier it is to work out whether the structure is viable and which part of the case needs the most attention.
Let to Buy Mortgage FAQs
Can I afford a let to buy mortgage?
Possibly, but affordability is only part of the picture.
A let to buy has to work in two ways at the same time: your current home must pass buy-to-let stress testing, and your new home must pass residential affordability. Many cases fail not because the borrower cannot afford it, but because one side of the structure does not meet a lender’s criteria.
Why is let to buy more difficult than a normal mortgage?
Because lenders are assessing two linked mortgages, not one.
Your existing property is treated as a rental investment, while your new purchase is assessed as a residential mortgage. The challenge is that these two assessments are not always aligned, and different lenders handle that interaction differently.
How much rent do I need for a let to buy?
More than just the mortgage payment.
Lenders usually apply a stressed interest rate and require the rent to exceed the mortgage by a margin. This means a property that appears to “break even” can still fall short under lender calculations.
How much can I borrow on a let to buy?
It depends on how the lender treats your existing property.
Some lenders effectively ignore the old mortgage if the rent covers it. Others include it fully or partially as a commitment. This is why borrowing amounts can vary significantly between lenders, even with identical income.
Can I use equity from my current home as a deposit?
Yes, but this is where many let to buy cases become unstable.
Releasing equity increases the borrowing on your current property, which can make it harder to pass rental stress testing. The structure has to work on both sides after the equity is released.
Do both mortgages have to be with the same lender?
Most lenders prefer not to offer both mortgages, but it depends on the case.
Some lenders allow the buy-to-let and residential mortgage to be arranged separately. Others apply restrictions, especially where equity is being released or the case is more complex.
Why do some let to buy applications get declined?
Usually because the structure does not fit the lender’s rules.
Common issues include:
- rental income failing stress tests
- not enough usable equity
- residential affordability being reduced
- lender policy conflicts between the two parts
In practice, the same case can be accepted by one lender and declined by another.
Is let to buy the same as buy to let?
No.
Buy-to-let is used to purchase an investment property. Let to buy involves keeping your current home, renting it out, and buying a new home to live in.
Is let to buy the same as consent to let?
No.
Consent to let allows you to rent out your current home temporarily while keeping your residential mortgage. Let to buy usually involves switching to a buy-to-let mortgage and arranging a new residential mortgage at the same time.
Does this calculator tell me if I will be approved?
No.
It shows whether the structure could work based on typical lending rules. It does not use live lender criteria and is not a lending decision.
