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Top slicing is where a lender uses your personal income to make up a shortfall when the rent on a buy to let does not quite cover the lender affordability test. Not every lender offers it, and the ones that do all set their own rules, but it is the difference between a case being declined and a case going through more often than most landlords realise.
It matters most in expensive areas with modest yields, which is a fair description of a lot of Hampshire.
Top slicing uses your personal income when the rent falls just short of the lender test.
Not every lender offers it, and the ones that do all set their own rules.
It closes a modest gap. It will not rescue a property that barely rents.
The rent usually still has to clear a floor on its own before income counts.
It matters most in expensive areas with modest yields, which describes much of Hampshire.
Why the rent falls short in the first place
Buy to let lending is not like residential lending. A lender does not mainly ask what you earn, it asks whether the rent covers the mortgage. That test is the interest coverage ratio, and it works on a stressed interest rate rather than the rate you actually pay.
The Prudential Regulation Authority sets the floor. Its supervisory statement on buy to let underwriting says a firm should assume a minimum borrower interest rate of 5.5% (paragraph 2.14). Separately, paragraph 2.13 says firms should have regard to a list of factors when working out the rate to test against, one of which is a minimum increase of two percentage points in buy to let interest rates.
Paragraph 2.12 is where five year fixes come in. It disapplies the requirement to consider likely rate movements over the following five years where the rate is fixed or capped for five years or more. In practice a lot of lenders respond by stressing those products at or close to the pay rate, which is why a five year fix often supports a larger loan. That is market practice built on the rule rather than something the rule spells out, the 5.5% floor still sits underneath, and the PRA still expects lenders to think about your refinancing risk at the end of the fixed period.
On top of that stressed rate, the lender wants the rent to exceed the interest by a margin. The common bands are 125% where the borrower is a basic rate taxpayer or the property is held in a limited company, and 145% for a higher rate taxpayer, with some lenders going higher again for additional rate. On a joint application the higher earner tax band usually sets the ratio for both.
Put those two things together and a property that produces a perfectly healthy real world profit can still fail the test on paper. That is the gap top slicing fills.
How top slicing actually works
The lender runs the standard rental calculation first. If the rent comfortably covers the requirement, your income usually matters far less than it would on a residential application, though plenty of lenders still set a minimum income to qualify at all, and if you have four or more mortgaged buy to let properties you are a portfolio landlord and the lender will look at your whole portfolio regardless of how well this one property stacks up.
If the rent falls short, a lender that offers top slicing will look at whether you have enough surplus personal income to cover the gap, and will assess that surplus the way a residential lender assesses affordability: income in, committed outgoings out, what is left over.
Income can usually come from employment, self employment, pension and often rental profit from other properties. What counts and how much of it counts varies a lot.
The important thing to understand is that top slicing is a top up, not a replacement. Lenders that offer it commonly still want the rent on its own to clear a floor, often around covering the stressed interest in full before your income is considered at all, so it closes a modest gap rather than rescuing a property that barely rents.
What lenders tend to look for
Since every lender writes its own policy, and those policies change, this is the shape of it rather than a checklist.
A minimum level of personal income, usually well into five figures, and often a higher threshold if you have never been a landlord before. Real surplus after your existing commitments, including your own residential mortgage and any other buy to let borrowing. A maximum loan to value, typically lower than the lender headline maximum. A floor on the rental calculation on its own, so the rent still has to do most of the work. And a list of exclusions, which commonly includes new build, let to buy, and capital raising for certain purposes.
First time landlords get looked at more carefully across the board, because the lender has no track record to price.
Speak to an expert
If a property is not quite stacking up on the rent, it is worth finding out whether the gap is bridgeable before you commit to anything. I am a whole of market broker and I handle buy to let cases in personal names and limited companies.
A case I placed
One example from my own casework, and one case is not a pattern, so treat it as an illustration of the mechanism rather than a guide to what will happen with yours.
The client was £150 a month short on the rental coverage calculation. Not a large gap, but on a straight rental assessment it was a decline. His personal income was £112,000 a year. I placed the case with a lender that would use top slicing, and it went through.
What made it work was the size of the gap relative to the income. £150 a month is the sort of shortfall top slicing is designed for. A property short by £600 a month is a different conversation, and personal income does not usually fix that.
When top slicing is not the answer
If the rent is a long way below the requirement, the honest answer is usually to borrow less rather than to hunt for a lender who will stretch. Reducing the loan reduces the interest, which reduces the rent you need, and it does it without tying your personal income to the property.
There are other levers too. A five year fix can help, for the reason set out above, though it ties you in for five years and those products are not always cheaper. Holding in a limited company attracts the lower coverage band with many lenders, though that is a decision with tax and cost consequences well beyond the mortgage and it belongs with your accountant, not with me. And if you are remortgaging rather than buying, staying with your existing lender on a product transfer usually avoids a fresh rental assessment altogether.
Which of those is right depends entirely on your circumstances, your tax position and what you are trying to achieve with the property. That is the conversation an advice appointment is for.
Do I raise it, or do you have to ask?
I raise it. If I can see a case is going to be tight on the rental calculation, top slicing is one of the first things I check for, because it changes which lenders are worth approaching at all. It is not something to discover after a decline.
If you want a rough idea of whether your rent clears the requirement before you speak to anyone, the buy to let rent calculator will give you a sense of it, and there is a fuller explanation in how much rent do I need for a buy to let mortgage.
If the rent on a property is not quite stacking up and you want to know whether the gap is bridgeable, that is worth a conversation before you commit. I am a mortgage broker in Winchester and I handle buy to let cases in personal names and limited companies. More background on the buy to let mortgage hub, and if a deal is ending, the buy to let remortgage page.
Source: Bank of England, SS13/16 underwriting standards for buy-to-let mortgage contracts. Paragraph references are to the version currently in force; a January 2026 update takes effect 1 January 2027.
Top slicing is one of several routes I look at when searching out the best buy to let mortgage for a client.
Top slicing is one corner of a wider question, whether you need personal income at all, which I answer in do you need a minimum income for a buy to let.
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Lender criteria change regularly and no lender is obliged to lend. Nothing here is a promise that any particular case will be approved, and the right route depends on your own circumstances. The Financial Conduct Authority does not regulate most buy to let mortgages.
