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 don’t always line up neatly.
This calculator tests whether those two sides hold together, factoring in rental stress testing and residential affordability — showing where your 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.
What This Let to Buy Calculator Shows That Most Don’t
- Which side is holding the move back: rental stress, buy-to-let loan-to-value, residential income or residential loan-to-value
- The real funding gap after purchase costs, property tax, existing mortgage, savings and both borrowing routes
- Whether the structure leans on the rental property, the residential mortgage, cash, or a balanced mix
- Whether the case clears with room, sits on a tight margin, or needs a structural change
- What could move the case back into range: rent, equity, income, commitments, deposit, purchase price or timing
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
The rent isn’t simply compared to the mortgage payment. Buy-to-let 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
I often see let to buy cases break down here. The problem isn’t always that the borrower cannot afford it. The problem is that the structure doesn’t 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 doesn’t meet the lender’s stress test
- there isn’t 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 don’t line up
Good cases can get stuck in between underwriting worlds.
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 of 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, but lenders don’t always treat them the same way. The problem with consent to let is that:
- It’s rare to be given permission
- Even if you get it, it’s often time limited as it’s meant to be a temporary solution
- Your new residential lender might not ignore your existing mortgage costs as it’s technically still a residential loan, not a buy-to-let.
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 were originally planning to sell.
Why Let-To-Buy Readiness Matters
Let-to-buy creates a double assessment.
You’re not only applying for a new residential mortgage. You’re also asking a lender to accept that your current home works as a rental property. That means two sets of criteria start interacting at once.
The lender has to understand:
- how your current property works as a buy-to-let
- whether the expected rent supports the new mortgage position
- how your personal income supports the residential mortgage
- whether your overall commitments still make sense
- whether the timing, deposit, equity and onward purchase line up
That’s why let-to-buy can get complicated quickly. A small weakness on one side can affect the other side. The rental calculation, personal affordability, existing mortgage balance, future home purchase and lender policy all stack together.
Before you rely on a let-to-buy plan, it helps to understand how lenders are likely to read the full picture. That’s the point of mortgage readiness: seeing how your position looks before you start making decisions around the next property.
See How Lenders Are Likely to Read Your Case
Most borrowers compare rates before they know whether a lender will actually like their case.
That’s how people waste time with the wrong bank, get weaker offers, or end up with avoidable declines.
The readiness check gives you an early read on how your case is likely to land, where the pressure points are, and whether lender choice needs more care.
- Avoid wrong lenders
- Spot pressure points
- Understand case fit
- Check before applying
See How Lenders Are Likely to Read Your Case
Mortgage Readiness Check
See how lenders will read your case.
Whether the income pattern looks stable enough to rely on, and how much of it they are prepared to include.
Let to Buy Mortgage Calculator FAQs
How do I know how much I can borrow on the residential side?
The residential side works like a normal home-mover affordability assessment, but the existing property can change the result.
Some lenders may ignore the old mortgage if the rental side works properly. Others may still include part of it as a commitment. Your income, deposit, credit profile and fixed monthly costs still matter.
If you want to test the residential part separately, use the residential borrowing calculator to check how your income and commitments could affect the onward purchase.
How do I know whether the buy-to-let side works?
The buy-to-let side depends mainly on rent, property value, mortgage balance and lender rental stress testing.
Lenders don’t simply compare the rent to the monthly payment. They usually test the rent against a stressed interest rate and require a margin above that figure. This means the property can look fine in real life but still fall short under a lender’s calculation.
If you want to test the rental property on its own, use the buy-to-let rental calculator to check whether the rent supports the borrowing.
Does let-to-buy work differently if I’m self-employed?
It can.
The rental side still needs to work as a buy-to-let, but the residential side depends on how lenders interpret your self-employed income. Some lenders use the latest year. Others average two years. Limited company directors can also be assessed differently depending on salary, dividends, retained profit and trading history.
That means a let-to-buy case can look strong on rental numbers but still become tighter on the residential side if the income needs more interpretation. If you’re self-employed, use the self-employed mortgage calculator to see how different lender approaches could affect the onward borrowing.
Does this let to buy calculator tell me if I’ll be approved?
No.
The calculator shows whether the structure looks workable based on typical lending mechanics. It doesn’t use live lender criteria and it isn’t a lending decision. A real application can still depend on lender policy, credit profile, income evidence, valuation, property type and underwriting. You should run a mortgage readiness check to uncover any obvious problems.
Can I use equity from my current home as the deposit?
Usually, yes. Many let-to-buy cases involve releasing equity from the current home to help fund the onward purchase.
The part borrowers often miss is that this changes the rental calculation. If you increase the borrowing on the current property, the rent has to support the larger buy-to-let mortgage. That can make the residential deposit look stronger while making the rental side weaker.
Do both mortgages have to be with the same lender?
No, often it’s not best.
Some let-to-buy cases use one lender for the buy-to-let mortgage and another lender for the new residential mortgage. The issue is usually timing and policy. Some lenders want both sides arranged together. Others mainly want evidence that the existing property will work as a rental after completion.
Is let-to-buy the same as consent to let?
No.
Consent to let usually means asking your current residential lender for permission to rent out the property temporarily. Let-to-buy usually means moving the current home onto a buy-to-let structure while arranging a new residential mortgage for the property you’re buying.
That difference matters because your new residential lender may treat the existing mortgage differently depending on whether it has been moved onto a buy-to-let basis.